/*
 * Copyright 2019 Google LLC
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "src/core/SkImageFilterTypes.h"

#include "include/core/SkAlphaType.h"
#include "include/core/SkBlendMode.h"
#include "include/core/SkCanvas.h"
#include "include/core/SkColor.h"
#include "include/core/SkColorType.h"
#include "include/core/SkImage.h"
#include "include/core/SkImageInfo.h"
#include "include/core/SkPaint.h"
#include "include/core/SkPicture.h"  // IWYU pragma: keep
#include "include/core/SkShader.h"
#include "include/private/base/SkFloatingPoint.h"
#include "src/core/SkImageFilter_Base.h"
#include "src/core/SkMatrixPriv.h"
#include "src/core/SkRectPriv.h"
#include "src/core/SkSpecialSurface.h"
#include "src/effects/colorfilters/SkColorFilterBase.h"

#ifdef SK_ENABLE_SKSL
#include "include/effects/SkRuntimeEffect.h"
#include "src/core/SkRuntimeEffectPriv.h"
#endif

#include <algorithm>

namespace skif {

namespace {

// This exists to cover up issues where infinite precision would produce integers but float
// math produces values just larger/smaller than an int and roundOut/In on bounds would produce
// nearly a full pixel error. One such case is crbug.com/1313579 where the caller has produced
// near integer CTM and uses integer crop rects that would grab an extra row/column of the
// input image when using a strict roundOut.
static constexpr float kRoundEpsilon = 1e-3f;

// If m is epsilon within the form [1 0 tx], this returns true and sets out to [tx, ty]
//                                 [0 1 ty]
//                                 [0 0 1 ]
// TODO: Use this in decomposeCTM() (and possibly extend it to support is_nearly_scale_translate)
// to be a little more forgiving on matrix types during layer configuration.
bool is_nearly_integer_translation(const LayerSpace<SkMatrix>& m,
                                   LayerSpace<SkIPoint>* out=nullptr) {
    float tx = SkScalarRoundToScalar(sk_ieee_float_divide(m.rc(0,2), m.rc(2,2)));
    float ty = SkScalarRoundToScalar(sk_ieee_float_divide(m.rc(1,2), m.rc(2,2)));
    SkMatrix expected = SkMatrix::MakeAll(1.f, 0.f, tx,
                                          0.f, 1.f, ty,
                                          0.f, 0.f, 1.f);
    for (int i = 0; i < 9; ++i) {
        if (!SkScalarNearlyEqual(expected.get(i), m.get(i), kRoundEpsilon)) {
            return false;
        }
    }

    if (out) {
        *out = LayerSpace<SkIPoint>({(int) tx, (int) ty});
    }
    return true;
}

// Assumes 'image' is decal-tiled, so everything outside the image bounds but inside dstBounds is
// transparent black, in which case the returned special image may be smaller than dstBounds.
//
// If 'clampSrcIfDisjoint' is true and the image bounds do not overlap with dstBounds, the closest
// edge/corner pixels of the image will be extracted, assuming it will be tiled with kClamp.
std::pair<sk_sp<SkSpecialImage>, LayerSpace<SkIPoint>> extract_subset(
        const SkSpecialImage* image,
        LayerSpace<SkIPoint> origin,
        const LayerSpace<SkIRect>& dstBounds,
        bool clampSrcIfDisjoint=false) {
    LayerSpace<SkIRect> imageBounds(SkIRect::MakeXYWH(origin.x(), origin.y(),
                                                      image->width(), image->height()));
    if (!imageBounds.intersect(dstBounds)) {
        if (clampSrcIfDisjoint) {
            auto edge = SkRectPriv::ClosestDisjointEdge(SkIRect(imageBounds), SkIRect(dstBounds));
            imageBounds = LayerSpace<SkIRect>(edge);
        } else {
            return {nullptr, {}};
        }
    }

    // Offset the image subset directly to avoid issues negating (origin). With the prior
    // intersection (bounds - origin) will be >= 0, but (bounds + (-origin)) may not, (e.g.
    // origin is INT_MIN).
    SkIRect subset = { imageBounds.left() - origin.x(),
                       imageBounds.top() - origin.y(),
                       imageBounds.right() - origin.x(),
                       imageBounds.bottom() - origin.y() };
    SkASSERT(subset.fLeft >= 0 && subset.fTop >= 0 &&
             subset.fRight <= image->width() && subset.fBottom <= image->height());

    return {image->makeSubset(subset), imageBounds.topLeft()};
}

void decompose_transform(const SkMatrix& transform, SkPoint representativePoint,
                         SkMatrix* postScaling, SkMatrix* scaling) {
    SkSize scale;
    if (transform.decomposeScale(&scale, postScaling)) {
        *scaling = SkMatrix::Scale(scale.fWidth, scale.fHeight);
    } else {
        // Perspective, which has a non-uniform scaling effect on the filter. Pick a single scale
        // factor that best matches where the filter will be evaluated.
        SkScalar approxScale = SkMatrixPriv::DifferentialAreaScale(transform, representativePoint);
        if (SkScalarIsFinite(approxScale) && !SkScalarNearlyZero(approxScale)) {
            // Now take the sqrt to go from an area scale factor to a scaling per X and Y
            approxScale = SkScalarSqrt(approxScale);
        } else {
            // The point was behind the W = 0 plane, so don't factor out any scale.
            approxScale = 1.f;
        }
        *postScaling = transform;
        postScaling->preScale(SkScalarInvert(approxScale), SkScalarInvert(approxScale));
        *scaling = SkMatrix::Scale(approxScale, approxScale);
    }
}

std::optional<LayerSpace<SkMatrix>> periodic_axis_transform(
        SkTileMode tileMode,
        const LayerSpace<SkIRect>& crop,
        const LayerSpace<SkIRect>& output) {
    if (tileMode == SkTileMode::kClamp || tileMode == SkTileMode::kDecal) {
        // Not periodic
        return {};
    }

    // Lift crop dimensions into 64 bit so that we can combine with 'output' without worrying about
    // overflowing 32 bits.
    double cropL = (double) crop.left();
    double cropT = (double) crop.top();
    double cropWidth = crop.right() - cropL;
    double cropHeight = crop.bottom() - cropT;

    // Calculate normalized periodic coordinates of 'output' relative to the 'crop' being tiled.
    int periodL = sk_double_floor2int((output.left() - cropL) / cropWidth);
    int periodT = sk_double_floor2int((output.top() - cropT) / cropHeight);
    int periodR = sk_double_ceil2int((output.right() - cropL) / cropWidth);
    int periodB = sk_double_ceil2int((output.bottom() - cropT) / cropHeight);

    if (periodR - periodL <= 1 && periodB - periodT <= 1) {
        // The tiling pattern won't be visible, so we can draw the image without tiling and an
        // adjusted transform. We calculate the final translation in double to be exact and then
        // verify that it can round-trip as a float.
        float sx = 1.f;
        float sy = 1.f;
        double tx = -cropL;
        double ty = -cropT;

        if (tileMode == SkTileMode::kMirror) {
            // Flip image when in odd periods on each axis.
            if (periodL % 2 != 0) {
                sx = -1.f;
                tx = cropWidth - tx;
            }
            if (periodT % 2 != 0) {
                sy = -1.f;
                ty = cropHeight - ty;
            }
        }
        // Now translate by periods and make relative to crop's top left again. Given 32-bit inputs,
        // the period * dimension shouldn't overflow 64-bits.
        tx += periodL * cropWidth + cropL;
        ty += periodT * cropHeight + cropT;

        // Representing the periodic tiling as a float SkMatrix would lose the pixel precision
        // required to represent it, so don't apply this optimization.
        if (sk_double_saturate2int(tx) != (float) tx ||
            sk_double_saturate2int(ty) != (float) ty) {
            return {};
        }

        SkMatrix periodicTransform;
        periodicTransform.setScaleTranslate(sx, sy, (float) tx, (float) ty);
        return LayerSpace<SkMatrix>(periodicTransform);
    } else {
        // Both low and high edges of the crop would be visible in 'output', or a mirrored
        // boundary is visible in 'output'. Just keep the periodic tiling.
        return {};
    }
}

#ifdef SK_ENABLE_SKSL

// Returns true if decal tiling an image with 'imageBounds' subject to 'transform', limited to
// the un-transformed 'sampleBounds' would exhibit significantly different visual quality from
// drawing the image with clamp tiling and limited geometrically to 'imageBounds'.
//
// Non-nearest-neighbor sampling across the image boundary with decal tiling introduces transparency
// If the transform's scale factor is near identity, the width of this transparent interpolation is
// visually consistent with the 1px anti-aliased edge produced by a SkCanvas::drawImage operation.
// If the scale factor is non-identity, the transparent ramp can get progressively smaller or larger
// as the relative size of a texel changes vs. the pixel size. While technically expected of decal
// tiling, it produces inconsistent rendering vs. when the transformed image is resolved to the
// actual layer resolution and then sampled by an image filter shader.
bool decal_tiling_differs_from_aa(const LayerSpace<SkMatrix> transform,
                                  const LayerSpace<SkIRect> imageBounds,
                                  const LayerSpace<SkIRect> sampleBounds,
                                  const SkSamplingOptions& sampling) {
    static constexpr SkSamplingOptions kNearestNeighbor = {};
    static constexpr SkSize kHalfPixel = {0.5f, 0.5f};
    static constexpr SkSize kCubicRadius = {1.5f, 1.5f};

    if (sampling == kNearestNeighbor) {
        // There's no interpolating between two samples, so the size of texels doesn't matter.
        return false;
    }

    LayerSpace<SkSize> expectedSampleRadius{sampling.useCubic ? kCubicRadius : kHalfPixel};
    LayerSpace<SkSize> sampleRadius = transform.mapSize(expectedSampleRadius);

    LayerSpace<SkRect> bufferedSampleBounds{sampleBounds};
    // First inset by half a pixel to account for where the dst sample coords actually are
    bufferedSampleBounds.inset(LayerSpace<SkSize>(kHalfPixel));
    // Then outset by the mapped radius
    bufferedSampleBounds.outset(sampleRadius);

    // If the sample bounds (including implicit samples from interpolation) are contained by the
    // transformed 'imageBounds', then the sampling would not access texels outside the image bounds
    if (SkRectPriv::QuadContainsRect(SkMatrix(transform),
                                     SkIRect(imageBounds),
                                     SkIRect(bufferedSampleBounds.roundOut()))) {
        return false;
    }

    // The decal sampling would be visible, but we only care if the width of the interpolation is
    // significantly different from an identity-scale.
    return !SkScalarNearlyEqual(sampleRadius.width(), expectedSampleRadius.width(), 0.1f) ||
           !SkScalarNearlyEqual(sampleRadius.height(), expectedSampleRadius.height(), 0.1f);
}

// The returned shader includes the transform as a local matrix.
sk_sp<SkShader> apply_decal(
        const LayerSpace<SkMatrix>& transform,
        sk_sp<SkSpecialImage> image,
        const LayerSpace<SkIRect>& sampleBounds,
        const SkSamplingOptions& sampling) {
    LayerSpace<SkIRect> imageBounds{image->dimensions()};
    if (!decal_tiling_differs_from_aa(transform, imageBounds, sampleBounds, sampling)) {
        // Decal the image as part of its sampling and apply the full transform afterwards
        return image->asShader(SkTileMode::kDecal, sampling, SkMatrix(transform));
    }

    // Otherwise we need to apply the decal in a coordinate space that matches the resolution of
    // the layer space. If the transform preserves rectangles, map the image bounds by the transform
    // so we can apply it before we evaluate the shader. Otherwise decompose the transform into
    // a non-scaling post-decal transform and a scaling pre-decal transform.
    const SkMatrix& m(transform);
    SkMatrix postDecal, preDecal;
    if (m.rectStaysRect()) {
        postDecal = SkMatrix::I();
        preDecal = m;
    } else {
        auto representativePoint = LayerSpace<SkRect>(imageBounds).center();
        decompose_transform(m, SkPoint(representativePoint), &postDecal, &preDecal);
    }

    // TODO(skbug:12784) - As part of fully supporting subsets in image shaders, it probably makes
    // sense to share the subset tiling logic that's in GrTextureEffect as dedicated SkShaders.
    // Graphite can then add those to its program as-needed vs. always doing shader-based tiling,
    // and CPU can have raster-pipeline tiling applied more flexibly than at the bitmap level. At
    // that point, this effect is redundant and can be replaced with the decal-subset shader.
    static const SkRuntimeEffect* effect = SkMakeRuntimeEffect(SkRuntimeEffect::MakeForShader,
        "uniform shader image;"
        "uniform float4 decalBounds;"

        "half4 main(float2 coord) {"
            "half4 d = half4(decalBounds - coord.xyxy) * half4(-1, -1, 1, 1);"
            "d = saturate(d + 0.5);"
            "return (d.x*d.y*d.z*d.w) * image.eval(coord);"
        "}");

    SkRuntimeShaderBuilder builder(sk_ref_sp(effect));
    builder.child("image") = image->asShader(SkTileMode::kClamp, sampling, preDecal);
    builder.uniform("decalBounds") = preDecal.mapRect(SkRect::Make(SkIRect(imageBounds)));

    sk_sp<SkShader> decalShader = builder.makeShader();
    if (decalShader && !postDecal.isIdentity()) {
        decalShader = decalShader->makeWithLocalMatrix(postDecal);
    }
    return decalShader;
}

#endif

// AutoSurface manages an SkSpecialSurface and canvas state to draw to a layer-space bounding box,
// and then snap it into a FilterResult. It provides operators to be used directly as a canvas,
// assuming surface creation succeeded. Usage:
//
//     AutoSurface surface{ctx, dstBounds, renderInParameterSpace}; // if true, concats layer matrix
//     if (surface) {
//         surface->drawFoo(...);
//     }
//     return surface.snap(); // Automatically handles failed allocations
class AutoSurface {
public:
    AutoSurface(const Context& ctx,
                const LayerSpace<SkIRect>& dstBounds,
                bool renderInParameterSpace,
                const SkSurfaceProps* props = nullptr)
            : fSurface(nullptr)
            , fDstBounds(dstBounds) {
        // We don't intersect by ctx.desiredOutput() and only use the Context to make the surface.
        // It is assumed the caller has already accounted for the desired output, or it's a
        // situation where the desired output shouldn't apply (e.g. this surface will be transformed
        // to align with the actual desired output via FilterResult metadata).
        fSurface = ctx.makeSurface(SkISize(fDstBounds.size()), props);
        if (!fSurface) {
            return;
        }

        // Configure the canvas
        SkCanvas* canvas = fSurface->getCanvas();
        // skbug.com/5075: GPU-backed special surfaces don't reset their contents.
        canvas->clear(SK_ColorTRANSPARENT);
        canvas->translate(-fDstBounds.left(), -fDstBounds.top()); // dst's origin adjustment

        if (renderInParameterSpace) {
            canvas->concat(ctx.mapping().layerMatrix());
        }
    }

    explicit operator bool() const { return SkToBool(fSurface); }

    SkCanvas* canvas() { SkASSERT(fSurface); return fSurface->getCanvas(); }
    SkCanvas* operator->() { SkASSERT(fSurface); return fSurface->getCanvas(); }

    // NOTE: This pair is equivalent to a FilterResult but we keep it this way for use by resolve(),
    // which wants them separate while the legacy imageAndOffset() function is around.
    std::pair<sk_sp<SkSpecialImage>, LayerSpace<SkIPoint>> snap() {
        if (fSurface) {
            return {fSurface->makeImageSnapshot(), fDstBounds.topLeft()};
        } else {
            return {nullptr, {}};
        }
    }

private:
    sk_sp<SkSpecialSurface> fSurface;
    LayerSpace<SkIRect> fDstBounds;
};

} // anonymous namespace

///////////////////////////////////////////////////////////////////////////////////////////////////

Context Context::MakeRaster(const ContextInfo& info) {
    // TODO (skbug:14286): Remove this forcing to 8888. Many legacy image filters only support
    // N32 on CPU, but once they are implemented in terms of draws and SkSL they will support
    // all color types, like the GPU backends.
    ContextInfo n32 = info;
    n32.fColorType = kN32_SkColorType;
    auto makeSurfaceCallback = [](const SkImageInfo& imageInfo,
                                  const SkSurfaceProps* props) {
        return SkSpecialSurfaces::MakeRaster(imageInfo, *props);
    };
    auto makeImageCallback = [](const SkIRect& subset,
                                sk_sp<SkImage> image,
                                const SkSurfaceProps& props) {
        return SkSpecialImages::MakeFromRaster(subset, image, props);
    };
    auto makeCachedBitmapCallback = [](const SkBitmap& data) {
        return SkImages::RasterFromBitmap(data);
    };
    return Context(n32, nullptr, makeSurfaceCallback, makeImageCallback, makeCachedBitmapCallback);
}

sk_sp<SkSpecialSurface> Context::makeSurface(const SkISize& size,
                                             const SkSurfaceProps* props) const {
    SkASSERT(fMakeSurfaceDelegate);
    if (!props) {
        props = &fInfo.fSurfaceProps;
    }

    SkImageInfo imageInfo = SkImageInfo::Make(size,
                                              fInfo.fColorType,
                                              kPremul_SkAlphaType,
                                              sk_ref_sp(fInfo.fColorSpace));
    return fMakeSurfaceDelegate(imageInfo, props);
}

sk_sp<SkSpecialImage> Context::makeImage(const SkIRect& subset, sk_sp<SkImage> image) const {
    SkASSERT(fMakeImageDelegate);
    return fMakeImageDelegate(subset, image, fInfo.fSurfaceProps);
}

sk_sp<SkImage> Context::getCachedBitmap(const SkBitmap& data) const {
    SkASSERT(fMakeCachedBitmapDelegate);
    return fMakeCachedBitmapDelegate(data);
}

///////////////////////////////////////////////////////////////////////////////////////////////////
// Mapping

SkIRect RoundOut(SkRect r) { return r.makeInset(kRoundEpsilon, kRoundEpsilon).roundOut(); }

SkIRect RoundIn(SkRect r) { return r.makeOutset(kRoundEpsilon, kRoundEpsilon).roundIn(); }

bool Mapping::decomposeCTM(const SkMatrix& ctm, const SkImageFilter* filter,
                           const skif::ParameterSpace<SkPoint>& representativePt) {
    SkMatrix remainder, layer;
    using MatrixCapability = SkImageFilter_Base::MatrixCapability;
    MatrixCapability capability =
            filter ? as_IFB(filter)->getCTMCapability() : MatrixCapability::kComplex;
    if (capability == MatrixCapability::kTranslate) {
        // Apply the entire CTM post-filtering
        remainder = ctm;
        layer = SkMatrix::I();
    } else if (ctm.isScaleTranslate() || capability == MatrixCapability::kComplex) {
        // Either layer space can be anything (kComplex) - or - it can be scale+translate, and the
        // ctm is. In both cases, the layer space can be equivalent to device space.
        remainder = SkMatrix::I();
        layer = ctm;
    } else {
        // This case implies some amount of sampling post-filtering, either due to skew or rotation
        // in the original matrix. As such, keep the layer matrix as simple as possible.
        decompose_transform(ctm, SkPoint(representativePt), &remainder, &layer);
    }

    SkMatrix invRemainder;
    if (!remainder.invert(&invRemainder)) {
        // Under floating point arithmetic, it's possible to decompose an invertible matrix into
        // a scaling matrix and a remainder and have the remainder be non-invertible. Generally
        // when this happens the scale factors are so large and the matrix so ill-conditioned that
        // it's unlikely that any drawing would be reasonable, so failing to make a layer is okay.
        return false;
    } else {
        fParamToLayerMatrix = layer;
        fLayerToDevMatrix = remainder;
        fDevToLayerMatrix = invRemainder;
        return true;
    }
}

bool Mapping::adjustLayerSpace(const SkMatrix& layer) {
    SkMatrix invLayer;
    if (!layer.invert(&invLayer)) {
        return false;
    }
    fParamToLayerMatrix.postConcat(layer);
    fDevToLayerMatrix.postConcat(layer);
    fLayerToDevMatrix.preConcat(invLayer);
    return true;
}

// Instantiate map specializations for the 6 geometric types used during filtering
template<>
SkRect Mapping::map<SkRect>(const SkRect& geom, const SkMatrix& matrix) {
    return geom.isEmpty() ? SkRect::MakeEmpty() : matrix.mapRect(geom);
}

template<>
SkIRect Mapping::map<SkIRect>(const SkIRect& geom, const SkMatrix& matrix) {
    if (geom.isEmpty()) {
        return SkIRect::MakeEmpty();
    }
    // Unfortunately, there is a range of integer values such that we have 1px precision as an int,
    // but less precision as a float. This can lead to non-empty SkIRects becoming empty simply
    // because of float casting. If we're already dealing with a float rect or having a float
    // output, that's what we're stuck with; but if we are starting form an irect and desiring an
    // SkIRect output, we go through efforts to preserve the 1px precision for simple transforms.
    if (matrix.isScaleTranslate()) {
        double l = (double)matrix.getScaleX()*geom.fLeft   + (double)matrix.getTranslateX();
        double r = (double)matrix.getScaleX()*geom.fRight  + (double)matrix.getTranslateX();
        double t = (double)matrix.getScaleY()*geom.fTop    + (double)matrix.getTranslateY();
        double b = (double)matrix.getScaleY()*geom.fBottom + (double)matrix.getTranslateY();
        return {sk_double_saturate2int(sk_double_floor(std::min(l, r) + kRoundEpsilon)),
                sk_double_saturate2int(sk_double_floor(std::min(t, b) + kRoundEpsilon)),
                sk_double_saturate2int(sk_double_ceil(std::max(l, r)  - kRoundEpsilon)),
                sk_double_saturate2int(sk_double_ceil(std::max(t, b)  - kRoundEpsilon))};
    } else {
        return RoundOut(matrix.mapRect(SkRect::Make(geom)));
    }
}

template<>
SkIPoint Mapping::map<SkIPoint>(const SkIPoint& geom, const SkMatrix& matrix) {
    SkPoint p = SkPoint::Make(SkIntToScalar(geom.fX), SkIntToScalar(geom.fY));
    matrix.mapPoints(&p, 1);
    return SkIPoint::Make(SkScalarRoundToInt(p.fX), SkScalarRoundToInt(p.fY));
}

template<>
SkPoint Mapping::map<SkPoint>(const SkPoint& geom, const SkMatrix& matrix) {
    SkPoint p;
    matrix.mapPoints(&p, &geom, 1);
    return p;
}

template<>
Vector Mapping::map<Vector>(const Vector& geom, const SkMatrix& matrix) {
    SkVector v = SkVector::Make(geom.fX, geom.fY);
    matrix.mapVectors(&v, 1);
    return Vector{v};
}

template<>
IVector Mapping::map<IVector>(const IVector& geom, const SkMatrix& matrix) {
    SkVector v = SkVector::Make(SkIntToScalar(geom.fX), SkIntToScalar(geom.fY));
    matrix.mapVectors(&v, 1);
    return IVector(SkScalarRoundToInt(v.fX), SkScalarRoundToInt(v.fY));
}

// Sizes are also treated as non-positioned values (although this assumption breaks down if there's
// perspective). Unlike vectors, we treat input sizes as specifying lengths of the local X and Y
// axes and return the lengths of those mapped axes.
template<>
SkSize Mapping::map<SkSize>(const SkSize& geom, const SkMatrix& matrix) {
    if (matrix.isScaleTranslate()) {
        // This is equivalent to mapping the two basis vectors and calculating their lengths.
        SkVector sizes = matrix.mapVector(geom.fWidth, geom.fHeight);
        return {SkScalarAbs(sizes.fX), SkScalarAbs(sizes.fY)};
    }

    SkVector xAxis = matrix.mapVector(geom.fWidth, 0.f);
    SkVector yAxis = matrix.mapVector(0.f, geom.fHeight);
    return {xAxis.length(), yAxis.length()};
}

template<>
SkISize Mapping::map<SkISize>(const SkISize& geom, const SkMatrix& matrix) {
    SkSize size = map(SkSize::Make(geom), matrix);
    return SkISize::Make(SkScalarCeilToInt(size.fWidth - kRoundEpsilon),
                         SkScalarCeilToInt(size.fHeight - kRoundEpsilon));
}

template<>
SkMatrix Mapping::map<SkMatrix>(const SkMatrix& m, const SkMatrix& matrix) {
    // If 'matrix' maps from the C1 coord space to the C2 coord space, and 'm' is a transform that
    // operates on, and outputs to, the C1 coord space, we want to return a new matrix that is
    // equivalent to 'm' that operates on and outputs to C2. This is the same as mapping the input
    // from C2 to C1 (matrix^-1), then transforming by 'm', and then mapping from C1 to C2 (matrix).
    SkMatrix inv;
    SkAssertResult(matrix.invert(&inv));
    inv.postConcat(m);
    inv.postConcat(matrix);
    return inv;
}

///////////////////////////////////////////////////////////////////////////////////////////////////
// LayerSpace<T>

// Match rounding tolerances of SkRects to SkIRects
LayerSpace<SkISize> LayerSpace<SkSize>::round() const {
    return LayerSpace<SkISize>(fData.toRound());
}
LayerSpace<SkISize> LayerSpace<SkSize>::ceil() const {
    return LayerSpace<SkISize>({SkScalarCeilToInt(fData.fWidth - kRoundEpsilon),
                                SkScalarCeilToInt(fData.fHeight - kRoundEpsilon)});
}
LayerSpace<SkISize> LayerSpace<SkSize>::floor() const {
    return LayerSpace<SkISize>({SkScalarFloorToInt(fData.fWidth + kRoundEpsilon),
                                SkScalarFloorToInt(fData.fHeight + kRoundEpsilon)});
}

LayerSpace<SkRect> LayerSpace<SkMatrix>::mapRect(const LayerSpace<SkRect>& r) const {
    return LayerSpace<SkRect>(Mapping::map(SkRect(r), fData));
}

// Effectively mapRect(SkRect).roundOut() but more accurate when the underlying matrix or
// SkIRect has large floating point values.
LayerSpace<SkIRect> LayerSpace<SkMatrix>::mapRect(const LayerSpace<SkIRect>& r) const {
    return LayerSpace<SkIRect>(Mapping::map(SkIRect(r), fData));
}

LayerSpace<SkPoint> LayerSpace<SkMatrix>::mapPoint(const LayerSpace<SkPoint>& p) const {
    return LayerSpace<SkPoint>(Mapping::map(SkPoint(p), fData));
}

LayerSpace<Vector> LayerSpace<SkMatrix>::mapVector(const LayerSpace<Vector>& v) const {
    return LayerSpace<Vector>(Mapping::map(Vector(v), fData));
}

LayerSpace<SkSize> LayerSpace<SkMatrix>::mapSize(const LayerSpace<SkSize>& s) const {
    return LayerSpace<SkSize>(Mapping::map(SkSize(s), fData));
}

bool LayerSpace<SkMatrix>::inverseMapRect(const LayerSpace<SkRect>& r,
                                          LayerSpace<SkRect>* out) const {
    SkRect mapped;
    if (r.isEmpty()) {
        // An empty input always inverse maps to an empty rect "successfully"
        *out = LayerSpace<SkRect>::Empty();
        return true;
    } else if (SkMatrixPriv::InverseMapRect(fData, &mapped, SkRect(r))) {
        *out = LayerSpace<SkRect>(mapped);
        return true;
    } else {
        return false;
    }
}

bool LayerSpace<SkMatrix>::inverseMapRect(const LayerSpace<SkIRect>& rect,
                                          LayerSpace<SkIRect>* out) const {
    if (rect.isEmpty()) {
        // An empty input always inverse maps to an empty rect "successfully"
        *out = LayerSpace<SkIRect>::Empty();
        return true;
    } else if (fData.isScaleTranslate()) { // Specialized inverse of 1px-preserving map<SkIRect>
        // A scale-translate matrix with a 0 scale factor is not invertible.
        if (fData.getScaleX() == 0.f || fData.getScaleY() == 0.f) {
            return false;
        }
        double l = (rect.left()   - (double)fData.getTranslateX()) / (double)fData.getScaleX();
        double r = (rect.right()  - (double)fData.getTranslateX()) / (double)fData.getScaleX();
        double t = (rect.top()    - (double)fData.getTranslateY()) / (double)fData.getScaleY();
        double b = (rect.bottom() - (double)fData.getTranslateY()) / (double)fData.getScaleY();

        SkIRect mapped{sk_double_saturate2int(sk_double_floor(std::min(l, r) + kRoundEpsilon)),
                       sk_double_saturate2int(sk_double_floor(std::min(t, b) + kRoundEpsilon)),
                       sk_double_saturate2int(sk_double_ceil(std::max(l, r)  - kRoundEpsilon)),
                       sk_double_saturate2int(sk_double_ceil(std::max(t, b)  - kRoundEpsilon))};
        *out = LayerSpace<SkIRect>(mapped);
        return true;
    } else {
        SkRect mapped;
        if (SkMatrixPriv::InverseMapRect(fData, &mapped, SkRect::Make(SkIRect(rect)))) {
            *out = LayerSpace<SkRect>(mapped).roundOut();
            return true;
        }
    }

    return false;
}

///////////////////////////////////////////////////////////////////////////////////////////////////
// FilterResult

sk_sp<SkSpecialImage> FilterResult::imageAndOffset(const Context& ctx, SkIPoint* offset) const {
    auto [image, origin] = this->resolve(ctx, fLayerBounds);
    *offset = SkIPoint(origin);
    return image;
}


bool FilterResult::modifiesPixelsBeyondImage(const LayerSpace<SkIRect>& dstBounds) const {
    // If there is no transparency-affecting color filter and it's just decal tiling, it doesn't
    // matter how the image geometry overlaps with the dst bounds.
    if (!(fColorFilter && as_CFB(fColorFilter)->affectsTransparentBlack()) &&
        fTileMode == SkTileMode::kDecal) {
        return false;
    }

    // If the base image completely covers the render bounds then the effects of tiling won't be
    // visible and it doesn't matter if any color filter affects transparent black.
    if (SkRectPriv::QuadContainsRect(SkMatrix(fTransform),
                                     SkIRect::MakeSize(fImage->dimensions()),
                                     SkIRect(dstBounds))) {
        return false;
    }

    // Otherwise tiling or transparency-affecting color filters will modify the pixels beyond
    // the image bounds that are still within render bounds.
    return true;
}

bool FilterResult::isCropped(const LayerSpace<SkMatrix>& xtraTransform,
                             const LayerSpace<SkIRect>& dstBounds) const {
    // Tiling and color-filtering can completely fill 'fLayerBounds' in which case its edge is
    // a transition from possibly non-transparent to definitely transparent color.
    bool fillsLayerBounds = this->modifiesPixelsBeyondImage(dstBounds);
    if (!fillsLayerBounds) {
        // When that's not the case, 'fLayerBounds' may still be important if it crops the
        // edges of the original transformed image itself.
        LayerSpace<SkIRect> imageBounds =
            fTransform.mapRect(LayerSpace<SkIRect>{fImage->dimensions()});
        fillsLayerBounds = !fLayerBounds.contains(imageBounds);
    }

    if (fillsLayerBounds) {
        // Some content (either the image itself, or tiling/color-filtering) can produce
        // non-transparent output beyond 'fLayerBounds'. 'fLayerBounds' can only be ignored if the
        // desired output is completely contained within it (i.e. the edges of 'fLayerBounds' are
        // not visible).
        // NOTE: For the identity transform, this is equal to !fLayerBounds.contains(dstBounds)
        return !SkRectPriv::QuadContainsRect(SkMatrix(xtraTransform),
                                             SkIRect(fLayerBounds),
                                             SkIRect(dstBounds));
    } else {
        // No part of the sampled and color-filtered image would produce non-transparent pixels
        // outside of 'fLayerBounds' so 'fLayerBounds' can be ignored.
        return false;
    }
}

void FilterResult::updateTileMode(const Context& ctx, SkTileMode tileMode) {
    if (fImage) {
        fTileMode = tileMode;
        if (tileMode != SkTileMode::kDecal) {
            fLayerBounds = ctx.desiredOutput();
        }
    }
}

FilterResult FilterResult::applyCrop(const Context& ctx,
                                     const LayerSpace<SkIRect>& crop,
                                     SkTileMode tileMode) const {
    static const LayerSpace<SkMatrix> kIdentity{SkMatrix::I()};

    if (crop.isEmpty() || ctx.desiredOutput().isEmpty()) {
        // An empty crop cannot be anything other than fully transparent
        return {};
    }

    // First, determine how this image's layer bounds interact with the crop rect, which determines
    // the portion of 'crop' that could have non-transparent content.
    LayerSpace<SkIRect> cropContent = crop;
    if (!fImage ||
        !cropContent.intersect(fLayerBounds)) {
        // The pixels within 'crop' would be fully transparent, and tiling won't change that.
        return {};
    }

    // Second, determine the subset of 'crop' that is relevant to ctx.desiredOutput().
    LayerSpace<SkIRect> fittedCrop = crop;
    if (tileMode == SkTileMode::kDecal || tileMode == SkTileMode::kClamp) {
        // For both decal/clamp, we only care about the pixels within crop that are in the desired
        // output, unless we are clamping and have to preserve edge pixels when there's no overlap.
        if (!fittedCrop.intersect(ctx.desiredOutput())) {
            if (tileMode == SkTileMode::kDecal) {
                // The desired output would be filled with transparent black.
                fittedCrop = LayerSpace<SkIRect>::Empty();
            } else {
                // We just need the closest row/column/corner of 'crop' to the desired output.
                auto edge = SkRectPriv::ClosestDisjointEdge(SkIRect(crop),
                                                            SkIRect(ctx.desiredOutput()));
                fittedCrop = LayerSpace<SkIRect>(edge);
            }
        }
    }

    // Third, check if there's overlap with the known non-transparent cropped content and what's
    // used to tile the desired output. If not, the image is known to be empty. This modifies
    // 'cropContent' and not 'fittedCrop' so that any transparent padding remains if we have to
    // apply repeat/mirror tiling to the original geometry.
    if (!cropContent.intersect(fittedCrop)) {
        return {};
    }

    // Fourth, a periodic tiling that covers the output with a single instance of the image can be
    // simplified to just a transform.
    auto periodicTransform = periodic_axis_transform(tileMode, fittedCrop, ctx.desiredOutput());
    if (periodicTransform) {
        return this->applyTransform(ctx, *periodicTransform, FilterResult::kDefaultSampling);
    }

    bool preserveTransparencyInCrop = false;
    if (tileMode == SkTileMode::kDecal) {
        // We can reduce the crop dimensions to what's non-transparent
        fittedCrop = cropContent;
    } else if (fittedCrop.contains(ctx.desiredOutput())) {
        tileMode = SkTileMode::kDecal;
        fittedCrop = ctx.desiredOutput();
    } else if (!cropContent.contains(fittedCrop)) {
        // There is transparency in fittedCrop that must be resolved in order to maintain the new
        // tiling geometry.
        preserveTransparencyInCrop = true;
        if (fTileMode == SkTileMode::kDecal && tileMode == SkTileMode::kClamp) {
            // include 1px buffer for transparency from original kDecal tiling
            cropContent.outset(skif::LayerSpace<SkISize>({1, 1}));
            SkAssertResult(fittedCrop.intersect(cropContent));
        }
    } // Otherwise cropContent == fittedCrop

    // Fifth, when the transform is an integer translation, any prior tiling and the new tiling
    // can sometimes be addressed analytically without producing a new image. Moving the crop into
    // the image dimensions allows future operations like applying a transform or color filter to
    // be composed without rendering a new image since there will not be an intervening crop.
    const bool doubleClamp = fTileMode == SkTileMode::kClamp && tileMode == SkTileMode::kClamp;
    LayerSpace<SkIPoint> origin;
    if (!preserveTransparencyInCrop &&
        is_nearly_integer_translation(fTransform, &origin) &&
        (doubleClamp || !this->modifiesPixelsBeyondImage(fittedCrop))) {
        // Since the transform is axis-aligned, the tile mode can be applied to the original
        // image pre-transformation and still be consistent with the 'crop' geometry. When the
        // original tile mode is decal, extract_subset is always valid. When the original mode is
        // mirror/repeat, !modifiesPixelsBeyondImage() ensures that 'fittedCrop' is contained within
        // the base image bounds, so extract_subset is valid. When the original mode is clamp
        // and the new mode is not clamp, that is also the case. When both modes are clamp, we have
        // to consider how 'fittedCrop' intersects (or doesn't) with the base image bounds.
        FilterResult restrictedOutput =
                extract_subset(fImage.get(), origin, fittedCrop, doubleClamp);
        // This does not rely on resolve() to call extract_subset() because it  will still render a
        // new image if there's a color filter. As such, we have to preserve the current color
        // filter on the new FilterResult.
        restrictedOutput.fColorFilter = fColorFilter;
        restrictedOutput.updateTileMode(ctx, tileMode);
        return restrictedOutput;
    } else if (tileMode == SkTileMode::kDecal) {
        // A decal crop can always be applied as the final operation by adjusting layer bounds, and
        // does not modify any prior tile mode.
        SkASSERT(!preserveTransparencyInCrop);
        FilterResult restrictedOutput = *this;
        restrictedOutput.fLayerBounds = fittedCrop;
        return restrictedOutput;
    } else {
        // There is a non-trivial transform to the image data that must be applied before the
        // non-decal tilemode is meant to be applied to the axis-aligned 'crop'.
        FilterResult tiled = this->resolve(ctx, fittedCrop, true);
        tiled.updateTileMode(ctx, tileMode);
        return tiled;
    }
}

FilterResult FilterResult::applyColorFilter(const Context& ctx,
                                            sk_sp<SkColorFilter> colorFilter) const {
    static const LayerSpace<SkMatrix> kIdentity{SkMatrix::I()};

    // A null filter is the identity, so it should have been caught during image filter DAG creation
    SkASSERT(colorFilter);

    if (ctx.desiredOutput().isEmpty()) {
        return {};
    }

    // Color filters are applied after the transform and image sampling, but before the fLayerBounds
    // crop. We can compose 'colorFilter' with any previously applied color filter regardless
    // of the transform/sample state, so long as it respects the effect of the current crop.
    LayerSpace<SkIRect> newLayerBounds = fLayerBounds;
    if (as_CFB(colorFilter)->affectsTransparentBlack()) {
        if (!fImage || !newLayerBounds.intersect(ctx.desiredOutput())) {
            // The current image's intersection with the desired output is fully transparent, but
            // the new color filter converts that into a non-transparent color. The desired output
            // is filled with this color, but use a 1x1 surface and clamp tiling.
            AutoSurface surface{ctx,
                                LayerSpace<SkIRect>{SkIRect::MakeXYWH(ctx.desiredOutput().left(),
                                                                      ctx.desiredOutput().top(),
                                                                      1, 1)},
                                /*renderInParameterSpace=*/false};
            if (surface) {
                SkPaint paint;
                paint.setColor4f(SkColors::kTransparent, /*colorSpace=*/nullptr);
                paint.setColorFilter(std::move(colorFilter));
                surface->drawPaint(paint);
            }
            FilterResult solidColor = surface.snap();
            solidColor.updateTileMode(ctx, SkTileMode::kClamp);
            return solidColor;
        }

        if (this->isCropped(kIdentity, ctx.desiredOutput())) {
            // Since 'colorFilter' modifies transparent black, the new result's layer bounds must
            // be the desired output. But if the current image is cropped we need to resolve the
            // image to avoid losing the effect of the current 'fLayerBounds'.
            newLayerBounds.outset(LayerSpace<SkISize>({1, 1}));
            SkAssertResult(newLayerBounds.intersect(ctx.desiredOutput()));
            FilterResult filtered = this->resolve(ctx, newLayerBounds,
                                                  /*preserveTransparency=*/true);
            filtered.fColorFilter = std::move(colorFilter);
            filtered.updateTileMode(ctx, SkTileMode::kClamp);
            return filtered;
        }

        // otherwise we can fill out to the desired output without worrying about losing the crop.
        newLayerBounds = ctx.desiredOutput();
    } else {
        if (!fImage || !newLayerBounds.intersect(ctx.desiredOutput())) {
            // The color filter does not modify transparent black, so it remains transparent
            return {};
        }
        // otherwise a non-transparent affecting color filter can always be lifted before any crop
        // because it does not change the "shape" of the prior FilterResult.
    }

    // If we got here we can compose the new color filter with the previous filter and the prior
    // layer bounds are either soft-cropped to the desired output, or we fill out the desired output
    // when the new color filter affects transparent black. We don't check if the entire composed
    // filter affects transparent black because earlier floods are restricted by the layer bounds.
    FilterResult filtered = *this;
    filtered.fLayerBounds = newLayerBounds;
    filtered.fColorFilter = SkColorFilters::Compose(std::move(colorFilter), fColorFilter);
    return filtered;
}

static bool compatible_sampling(const SkSamplingOptions& currentSampling,
                                bool currentXformWontAffectNearest,
                                SkSamplingOptions* nextSampling,
                                bool nextXformWontAffectNearest) {
    // Both transforms could perform non-trivial sampling, but if they are similar enough we
    // assume performing one non-trivial sampling operation with the concatenated transform will
    // not be visually distinguishable from sampling twice.
    // TODO(michaelludwig): For now ignore mipmap policy, SkSpecialImages are not supposed to be
    // drawn with mipmapping, and the majority of filter steps produce images that are at the
    // proper scale and do not define mip levels. The main exception is the ::Image() filter
    // leaf but that doesn't use this system yet.
    if (currentSampling.isAniso() && nextSampling->isAniso()) {
        // Assume we can get away with one sampling at the highest anisotropy level
        *nextSampling =  SkSamplingOptions::Aniso(std::max(currentSampling.maxAniso,
                                                           nextSampling->maxAniso));
        return true;
    } else if (currentSampling.isAniso() && nextSampling->filter == SkFilterMode::kLinear) {
        // Assume we can get away with the current anisotropic filter since the next is linear
        *nextSampling = currentSampling;
        return true;
    } else if (nextSampling->isAniso() && currentSampling.filter == SkFilterMode::kLinear) {
        // Mirror of the above, assume we can just get away with next's anisotropic filter
        return true;
    } else if (currentSampling.useCubic && (nextSampling->filter == SkFilterMode::kLinear ||
                                            (nextSampling->useCubic &&
                                             currentSampling.cubic.B == nextSampling->cubic.B &&
                                             currentSampling.cubic.C == nextSampling->cubic.C))) {
        // Assume we can get away with the current bicubic filter, since the next is the same
        // or a bilerp that can be upgraded.
        *nextSampling = currentSampling;
        return true;
    } else if (nextSampling->useCubic && currentSampling.filter == SkFilterMode::kLinear) {
        // Mirror of the above, assume we can just get away with next's cubic resampler
        return true;
    } else if (currentSampling.filter == SkFilterMode::kLinear &&
               nextSampling->filter == SkFilterMode::kLinear) {
        // Assume we can get away with a single bilerp vs. the two
        return true;
    } else if (nextSampling->filter == SkFilterMode::kNearest && currentXformWontAffectNearest) {
        // The next transform and nearest-neighbor filtering isn't impacted by the current transform
        SkASSERT(currentSampling.filter == SkFilterMode::kLinear);
        return true;
    } else if (currentSampling.filter == SkFilterMode::kNearest && nextXformWontAffectNearest) {
        // The next transform doesn't change the nearest-neighbor filtering of the current transform
        SkASSERT(nextSampling->filter == SkFilterMode::kLinear);
        *nextSampling = currentSampling;
        return true;
    } else {
        // The current or next sampling is nearest neighbor, and will produce visible texels
        // oriented with the current transform; assume this is a desired effect and preserve it.
        return false;
    }
}

FilterResult FilterResult::applyTransform(const Context& ctx,
                                          const LayerSpace<SkMatrix> &transform,
                                          const SkSamplingOptions &sampling) const {
    if (!fImage || ctx.desiredOutput().isEmpty()) {
        // Transformed transparent black remains transparent black.
        SkASSERT(!fColorFilter);
        return {};
    }

    // Extract the sampling options that matter based on the current and next transforms.
    // We make sure the new sampling is bilerp (default) if the new transform doesn't matter
    // (and assert that the current is bilerp if its transform didn't matter). Bilerp can be
    // maximally combined, so simplifies the logic in compatible_sampling().
    const bool currentXformIsInteger = is_nearly_integer_translation(fTransform);
    const bool nextXformIsInteger = is_nearly_integer_translation(transform);

    SkASSERT(!currentXformIsInteger || fSamplingOptions == kDefaultSampling);
    SkSamplingOptions nextSampling = nextXformIsInteger ? kDefaultSampling : sampling;

    // Determine if the image is being visibly cropped by the layer bounds, in which case we can't
    // merge this transform with any previous transform (unless the new transform is an integer
    // translation in which case any visible edge is aligned with the desired output and can be
    // resolved by intersecting the transformed layer bounds and the output bounds).
    bool isCropped = !nextXformIsInteger && this->isCropped(transform, ctx.desiredOutput());

    FilterResult transformed;
    if (!isCropped && compatible_sampling(fSamplingOptions, currentXformIsInteger,
                                          &nextSampling, nextXformIsInteger)) {
        // We can concat transforms and 'nextSampling' will be either fSamplingOptions,
        // sampling, or a merged combination depending on the two transforms in play.
        transformed = *this;
    } else {
        // We'll have to resolve this FilterResult first before 'transform' and 'sampling' can be
        // correctly evaluated. 'nextSampling' will always be 'sampling'.
        LayerSpace<SkIRect> tightBounds;
        if (transform.inverseMapRect(ctx.desiredOutput(), &tightBounds)) {
            transformed = this->resolve(ctx, tightBounds);
        }

        if (!transformed.fImage) {
            // Transform not invertible or resolve failed to create an image
            return {};
        }
    }

    transformed.fSamplingOptions = nextSampling;
    transformed.fTransform.postConcat(transform);
    // Rebuild the layer bounds and then restrict to the current desired output. The original value
    // of fLayerBounds includes the image mapped by the original fTransform as well as any
    // accumulated soft crops from desired outputs of prior stages. To prevent discarding that info,
    // we map fLayerBounds by the additional transform, instead of re-mapping the image bounds.
    transformed.fLayerBounds = transform.mapRect(transformed.fLayerBounds);
    if (!transformed.fLayerBounds.intersect(ctx.desiredOutput())) {
        // The transformed output doesn't touch the desired, so it would just be transparent black.
        // TODO: This intersection only applies when the tile mode is kDecal.
        return {};
    }

    return transformed;
}

std::pair<sk_sp<SkSpecialImage>, LayerSpace<SkIPoint>> FilterResult::resolve(
        const Context& ctx,
        LayerSpace<SkIRect> dstBounds,
        bool preserveTransparency) const {
    // The layer bounds is the final clip, so it can always be used to restrict 'dstBounds'. Even
    // if there's a non-decal tile mode or transparent-black affecting color filter, those floods
    // are restricted to fLayerBounds.
    if (!fImage || (!preserveTransparency && !dstBounds.intersect(fLayerBounds))) {
        return {nullptr, {}};
    }

    // If we have any extra effect to apply, there's no point in trying to extract a subset.
    const bool subsetCompatible = !fColorFilter &&
                                  fTileMode == SkTileMode::kDecal &&
                                  !preserveTransparency;

    // TODO(michaelludwig): If we get to the point where all filter results track bounds in
    // floating point, then we can extend this case to any S+T transform.
    LayerSpace<SkIPoint> origin;
    if (subsetCompatible && is_nearly_integer_translation(fTransform, &origin)) {
        return extract_subset(fImage.get(), origin, dstBounds);
    } // else fall through and attempt a draw

    // Don't use context properties to avoid DMSAA on internal stages of filter evaluation.
    SkSurfaceProps props = {};
    AutoSurface surface{ctx, dstBounds, /*renderInParameterSpace=*/false, &props};
    if (surface) {
        this->draw(surface.canvas(), dstBounds);
    }
    return surface.snap();
}

void FilterResult::draw(SkCanvas* canvas, const LayerSpace<SkIRect>& dstBounds) const {
    if (!fImage) {
        return;
    }

    // When this is called by resolve(), the surface and canvas matrix are such that this clip is
    // trivially a no-op, but including the clip means draw() works correctly in other scenarios.
    canvas->clipIRect(SkIRect(fLayerBounds));

    SkPaint paint;
    paint.setAntiAlias(true);
    paint.setBlendMode(SkBlendMode::kSrcOver);
    paint.setColorFilter(fColorFilter);

    // If we are an integer translate, the default bilinear sampling *should* be equivalent to
    // nearest-neighbor. Going through the direct image-drawing path tends to detect this
    // and reduce sampling automatically. When we have to use an image shader, this isn't
    // detected and some GPUs' linear filtering doesn't exactly match nearest-neighbor and can
    // lead to leaks beyond the image's subset. Detect and reduce sampling explicitly.
    SkSamplingOptions sampling = fSamplingOptions;
    if (sampling == kDefaultSampling && is_nearly_integer_translation(fTransform)) {
        sampling = {};
    }

    if (this->modifiesPixelsBeyondImage(dstBounds)) {
#ifdef SK_ENABLE_SKSL
        if (fTileMode == SkTileMode::kDecal) {
            // apply_decal consumes the transform, so we don't modify the canvas
            paint.setShader(apply_decal(fTransform, fImage, fLayerBounds, sampling));
        } else
#endif
        {
            // For clamp/repeat/mirror, tiling at the layer resolution vs. resolving the image to
            // the layer resolution and then tiling produces much more compatible results than
            // decal would, so just always use a simple shader. If we don't have SkSL to let us use
            // apply_decal, this might introduce some distortion if there was a deferred transform
            // with a high scale factor, but this is a rare scenario.
            paint.setShader(fImage->asShader(fTileMode, sampling, SkMatrix(fTransform)));
        }
        // Fill the canvas with the shader, relying on it to do the transform
        canvas->drawPaint(paint);
    } else {
        canvas->concat(SkMatrix(fTransform)); // src's origin is embedded in fTransform
        fImage->draw(canvas, 0.f, 0.f, sampling, &paint);
    }
}

sk_sp<SkShader> FilterResult::asShader(const Context& ctx,
                                       const SkSamplingOptions& xtraSampling,
                                       SkEnumBitMask<ShaderFlags> flags,
                                       const LayerSpace<SkIRect>& sampleBounds) const {
    if (!fImage) {
        return nullptr;
    }
    // Even if flags don't force resolving the filter result to an axis-aligned image, if the
    // extra sampling to be applied is not compatible with the accumulated transform and sampling,
    // or if the logical image is cropped by the layer bounds, the FilterResult will need to be
    // resolved to an image before we wrap it as an SkShader. When checking if cropped, we use the
    // FilterResult's layer bounds instead of the context's desired output, assuming that the layer
    // bounds reflect the bounds of the coords a parent shader will pass to eval().
    const bool currentXformIsInteger = is_nearly_integer_translation(fTransform);
    const bool nextXformIsInteger = !(flags & ShaderFlags::kNonTrivialSampling);

    SkSamplingOptions sampling = xtraSampling;
    const bool needsResolve =
            // Deferred calculations on the input would be repeated with each sample
            (flags & ShaderFlags::kSampledRepeatedly &&
             (fColorFilter || !SkColorSpace::Equals(fImage->getColorSpace(), ctx.colorSpace()))) ||
            // The deferred sampling options can't be merged with the one requested
            !compatible_sampling(fSamplingOptions, currentXformIsInteger,
                                 &sampling, nextXformIsInteger) ||
            // The deferred edge of the layer bounds is visible to sampling
            this->isCropped(LayerSpace<SkMatrix>(SkMatrix::I()), sampleBounds);

    // Downgrade to nearest-neighbor if the sequence of sampling doesn't do anything
    if (sampling == kDefaultSampling && nextXformIsInteger &&
        (needsResolve || currentXformIsInteger)) {
        sampling = {};
    }

    sk_sp<SkShader> shader;
    if (needsResolve) {
        // The resolve takes care of fTransform (sans origin), fTileMode, fColorFilter, and
        // fLayerBounds
        auto [pixels, origin] = this->resolve(ctx, fLayerBounds);
        if (pixels) {
            shader = pixels->asShader(SkTileMode::kDecal, sampling,
                                      SkMatrix::Translate(origin.x(), origin.y()));
        }
    } else {
        // Since we didn't need to resolve, we know the content being sampled isn't cropped by
        // fLayerBounds. fTransform and fColorFilter are handled in the shader directly.
#ifdef SK_ENABLE_SKSL
        if (fTileMode == SkTileMode::kDecal) {
            shader = apply_decal(fTransform, fImage, sampleBounds, sampling);
        } else
#endif
        {
            shader = fImage->asShader(fTileMode, sampling, SkMatrix(fTransform));
        }

        if (shader && fColorFilter) {
            shader = shader->makeWithColorFilter(fColorFilter);
        }
    }

    return shader;
}

FilterResult FilterResult::MakeFromPicture(const Context& ctx,
                                           sk_sp<SkPicture> pic,
                                           ParameterSpace<SkRect> cullRect) {
    if (!pic) {
        return {};
    }

    LayerSpace<SkIRect> dstBounds = ctx.mapping().paramToLayer(cullRect).roundOut();
    if (!dstBounds.intersect(ctx.desiredOutput())) {
        return {};
    }

    // Given the standard usage of the picture image filter (i.e., to render content at a fixed
    // resolution that, most likely, differs from the screen's) disable LCD text by removing any
    // knowledge of the pixel geometry.
    // TODO: Should we just generally do this for layers with image filters? Or can we preserve it
    // for layers that are still axis-aligned?
    SkSurfaceProps props = ctx.surfaceProps().cloneWithPixelGeometry(kUnknown_SkPixelGeometry);
    AutoSurface surface{ctx, dstBounds, /*renderInParameterSpace=*/true, &props};
    if (surface) {
        surface->clipRect(SkRect(cullRect));
        surface->drawPicture(std::move(pic));
    }
    return surface.snap();
}

FilterResult FilterResult::MakeFromShader(const Context& ctx,
                                          sk_sp<SkShader> shader,
                                          bool dither) {
    if (!shader) {
        return {};
    }

    AutoSurface surface{ctx, ctx.desiredOutput(), /*renderInParameterSpace=*/true};
    if (surface) {
        SkPaint paint;
        paint.setShader(shader);
        paint.setDither(dither);
        surface->drawPaint(paint);
    }
    return surface.snap();
}

FilterResult FilterResult::MakeFromImage(const Context& ctx,
                                         sk_sp<SkImage> image,
                                         const SkRect& srcRect,
                                         const ParameterSpace<SkRect>& dstRect,
                                         const SkSamplingOptions& sampling) {
    if (!image) {
        return {};
    }

    // Check for direct conversion to an SkSpecialImage and then FilterResult. Eventually this
    // whole function should be replaceable with:
    //    FilterResult(fImage, fSrcRect, fDstRect).applyTransform(mapping.layerMatrix(), fSampling);
    SkIRect srcSubset = RoundOut(srcRect);
    if (SkRect::Make(srcSubset) == srcRect) {
        // Construct an SkSpecialImage from the subset directly instead of drawing.
        sk_sp<SkSpecialImage> specialImage = ctx.makeImage(srcSubset, std::move(image));

        // Treat the srcRect's top left as "layer" space since we are folding the src->dst transform
        // and the param->layer transform into a single transform step.
        skif::FilterResult subset{std::move(specialImage),
                                  skif::LayerSpace<SkIPoint>(srcSubset.topLeft())};
        SkMatrix transform = SkMatrix::Concat(ctx.mapping().layerMatrix(),
                                              SkMatrix::RectToRect(srcRect, SkRect(dstRect)));
        return subset.applyTransform(ctx, skif::LayerSpace<SkMatrix>(transform), sampling);
    }

    // For now, draw the src->dst subset of image into a new image.
    LayerSpace<SkIRect> dstBounds = ctx.mapping().paramToLayer(dstRect).roundOut();
    if (!dstBounds.intersect(ctx.desiredOutput())) {
        return {};
    }

    AutoSurface surface{ctx, dstBounds, /*renderInParameterSpace=*/true};
    if (surface) {
        SkPaint paint;
        paint.setAntiAlias(true);
        surface->drawImageRect(image, srcRect, SkRect(dstRect), sampling, &paint,
                               SkCanvas::kStrict_SrcRectConstraint);
    }
    return surface.snap();
}

///////////////////////////////////////////////////////////////////////////////////////////////////
// FilterResult::Builder

FilterResult::Builder::Builder(const Context& context) : fContext(context) {}
FilterResult::Builder::~Builder() = default;

SkSpan<sk_sp<SkShader>> FilterResult::Builder::createInputShaders(
        const LayerSpace<SkIRect>& outputBounds,
        bool evaluateInParameterSpace) {
    SkEnumBitMask<ShaderFlags> xtraFlags = ShaderFlags::kNone;
    SkMatrix layerToParam;
    if (evaluateInParameterSpace) {
        // The FilterResult is meant to be sampled in layer space, but the shader this is feeding
        // into is being sampled in parameter space. Add the inverse of the layerMatrix() (i.e.
        // layer to parameter space) as a local matrix to convert from the parameter-space coords
        // of the outer shader to the layer-space coords of the FilterResult).
        SkAssertResult(fContext.mapping().layerMatrix().invert(&layerToParam));
        // Automatically add nonTrivial sampling if the layer-to-parameter space mapping isn't
        // also pixel aligned.
        if (!is_nearly_integer_translation(LayerSpace<SkMatrix>(layerToParam))) {
            xtraFlags |= ShaderFlags::kNonTrivialSampling;
        }
    }

    fInputShaders.reserve(fInputs.size());
    for (const SampledFilterResult& input : fInputs) {
        // Assume the input shader will be evaluated once per pixel in the output unless otherwise
        // specified when the FilterResult was added to the builder.
        auto sampleBounds = input.fSampleBounds ? *input.fSampleBounds : outputBounds;
        auto shader = input.fImage.asShader(fContext,
                                            input.fSampling,
                                            input.fFlags | xtraFlags,
                                            sampleBounds);
        if (evaluateInParameterSpace && shader) {
            shader = shader->makeWithLocalMatrix(layerToParam);
        }
        fInputShaders.push_back(std::move(shader));
    }
    return SkSpan<sk_sp<SkShader>>(fInputShaders);
}

LayerSpace<SkIRect> FilterResult::Builder::outputBounds(
        std::optional<LayerSpace<SkIRect>> explicitOutput) const {
    // Pessimistically assume output fills the full desired bounds
    LayerSpace<SkIRect> output = fContext.desiredOutput();
    if (explicitOutput.has_value()) {
        // Intersect with the provided explicit bounds
        if (!output.intersect(*explicitOutput)) {
            return LayerSpace<SkIRect>::Empty();
        }
    }
    return output;
}

FilterResult FilterResult::Builder::drawShader(sk_sp<SkShader> shader,
                                               const LayerSpace<SkIRect>& outputBounds,
                                               bool evaluateInParameterSpace) const {
    SkASSERT(!outputBounds.isEmpty()); // Should have been rejected before we created shaders
    if (!shader) {
        return {};
    }

    AutoSurface surface{fContext, outputBounds, evaluateInParameterSpace};
    if (surface) {
        SkPaint paint;
        paint.setShader(std::move(shader));
        surface->drawPaint(paint);
    }
    return surface.snap();
}

FilterResult FilterResult::Builder::merge() {
    if (fInputs.empty()) {
        return {};
    } else if (fInputs.size() == 1) {
        SkASSERT(!fInputs[0].fSampleBounds.has_value() &&
                 fInputs[0].fSampling == kDefaultSampling &&
                 fInputs[0].fFlags == ShaderFlags::kNone);
        return fInputs[0].fImage;
    }

    const auto mergedBounds = LayerSpace<SkIRect>::Union(
            (int) fInputs.size(),
            [this](int i) { return fInputs[i].fImage.layerBounds(); });
    const auto outputBounds = this->outputBounds(mergedBounds);

    AutoSurface surface{fContext, outputBounds, /*renderInParameterSpace=*/false};
    if (surface) {
        for (const SampledFilterResult& input : fInputs) {
            SkASSERT(!input.fSampleBounds.has_value() &&
                     input.fSampling == kDefaultSampling &&
                     input.fFlags == ShaderFlags::kNone);
            surface->save();
            input.fImage.draw(surface.canvas(), outputBounds);
            surface->restore();
        }
    }
    return surface.snap();
}

} // end namespace skif
