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* 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 "src/core/SkImageFilter_Base.h"
#include "src/core/SkMatrixPriv.h"
// 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 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;
// Both [I]Vectors and Sk[I]Sizes are transformed as non-positioned values, i.e. go through
// mapVectors() not mapPoints().
static SkIVector map_as_vector(int32_t x, int32_t y, const SkMatrix& matrix) {
SkVector v = SkVector::Make(SkIntToScalar(x), SkIntToScalar(y));
matrix.mapVectors(&v, 1);
return SkIVector::Make(SkScalarRoundToInt(v.fX), SkScalarRoundToInt(v.fY));
static SkVector map_as_vector(SkScalar x, SkScalar y, const SkMatrix& matrix) {
SkVector v = SkVector::Make(x, y);
matrix.mapVectors(&v, 1);
return v;
// 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.
static bool is_nearly_integer_translation(const skif::LayerSpace<SkMatrix>& m,
skif::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 = skif::LayerSpace<SkIPoint>({(int) tx, (int) ty});
return true;
static SkRect map_rect(const SkMatrix& matrix, const SkRect& rect) {
if (rect.isEmpty()) {
return SkRect::MakeEmpty();
return matrix.mapRect(rect);
static SkIRect map_rect(const SkMatrix& matrix, const SkIRect& rect) {
if (rect.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()*rect.fLeft + (double)matrix.getTranslateX();
double r = (double)matrix.getScaleX()*rect.fRight + (double)matrix.getTranslateX();
double t = (double)matrix.getScaleY()*rect.fTop + (double)matrix.getTranslateY();
double b = (double)matrix.getScaleY()*rect.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 skif::RoundOut(matrix.mapRect(SkRect::Make(rect)));
namespace skif {
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;
SkSize decomposed;
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 if (ctm.decomposeScale(&decomposed, &remainder)) {
// 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.
layer = SkMatrix::Scale(decomposed.fWidth, decomposed.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 scale = SkMatrixPriv::DifferentialAreaScale(ctm, SkPoint(representativePt));
if (SkScalarIsFinite(scale) && !SkScalarNearlyZero(scale)) {
// Now take the sqrt to go from an area scale factor to a scaling per X and Y
// FIXME: It would be nice to be able to choose a non-uniform scale.
scale = SkScalarSqrt(scale);
} else {
// The representative point was behind the W = 0 plane, so don't factor out any scale.
// NOTE: This makes remainder and layer the same as the MatrixCapability::Translate case
scale = 1.f;
remainder = ctm;
remainder.preScale(SkScalarInvert(scale), SkScalarInvert(scale));
layer = SkMatrix::Scale(scale, scale);
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;
return true;
// Instantiate map specializations for the 6 geometric types used during filtering
SkRect Mapping::map<SkRect>(const SkRect& geom, const SkMatrix& matrix) {
return map_rect(matrix, geom);
SkIRect Mapping::map<SkIRect>(const SkIRect& geom, const SkMatrix& matrix) {
return map_rect(matrix, geom);
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));
SkPoint Mapping::map<SkPoint>(const SkPoint& geom, const SkMatrix& matrix) {
SkPoint p;
matrix.mapPoints(&p, &geom, 1);
return p;
IVector Mapping::map<IVector>(const IVector& geom, const SkMatrix& matrix) {
return IVector(map_as_vector(geom.fX, geom.fY, matrix));
Vector Mapping::map<Vector>(const Vector& geom, const SkMatrix& matrix) {
return Vector(map_as_vector(geom.fX, geom.fY, matrix));
SkISize Mapping::map<SkISize>(const SkISize& geom, const SkMatrix& matrix) {
SkIVector v = map_as_vector(geom.fWidth, geom.fHeight, matrix);
return SkISize::Make(v.fX, v.fY);
SkSize Mapping::map<SkSize>(const SkSize& geom, const SkMatrix& matrix) {
SkVector v = map_as_vector(geom.fWidth, geom.fHeight, matrix);
return SkSize::Make(v.fX, v.fY);
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;
return inv;
LayerSpace<SkRect> LayerSpace<SkMatrix>::mapRect(const LayerSpace<SkRect>& r) const {
return LayerSpace<SkRect>(map_rect(fData, SkRect(r)));
LayerSpace<SkIRect> LayerSpace<SkMatrix>::mapRect(const LayerSpace<SkIRect>& r) const {
return LayerSpace<SkIRect>(map_rect(fData, SkIRect(r)));
sk_sp<SkSpecialImage> FilterResult::imageAndOffset(SkIPoint* offset) const {
auto [image, origin] = this->resolve(fLayerBounds);
*offset = SkIPoint(origin);
return image;
FilterResult FilterResult::applyCrop(const Context& ctx,
const LayerSpace<SkIRect>& crop) const {
LayerSpace<SkIRect> tightBounds = crop;
// TODO(michaelludwig): Intersecting to the target output is only valid when the crop has
// decal tiling (the only current option).
if (!fImage || !tightBounds.intersect(ctx.desiredOutput())) {
// The desired output would be filled with transparent black.
return {};
if (crop.contains(fLayerBounds)) {
// The original crop does not affect the image (although the context's desired output might)
// We can tighten fLayerBounds to the desired output without resolving the image, regardless
// of the transform type.
// TODO(michaelludwig): If the crop would use mirror or repeat, the above isn't true.
FilterResult restrictedOutput = *this;
return restrictedOutput;
} else {
return this->resolve(tightBounds);
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,
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) {
// Transformed transparent black remains transparent black.
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;
FilterResult transformed;
if (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'.
transformed = this->resolve(fLayerBounds);
transformed.concatTransform(transform, nextSampling, ctx.desiredOutput());
if (transformed.layerBounds().isEmpty()) {
return {};
} else {
return transformed;
void FilterResult::concatTransform(const LayerSpace<SkMatrix>& transform,
const SkSamplingOptions& newSampling,
const LayerSpace<SkIRect>& desiredOutput) {
if (!fImage) {
// Under normal circumstances, concatTransform() will only be called when we have an image,
// but if resolve() fails to make a special surface, we may end up here at which point
// doing nothing further is appropriate.
fSamplingOptions = newSampling;
// 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.
fLayerBounds = transform.mapRect(fLayerBounds);
if (!fLayerBounds.intersect(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.
fLayerBounds = LayerSpace<SkIRect>::Empty();
std::pair<sk_sp<SkSpecialImage>, LayerSpace<SkIPoint>> FilterResult::resolve(
LayerSpace<SkIRect> dstBounds) const {
// TODO(michaelludwig): Only valid for kDecal, although kClamp would only need 1 extra
// pixel of padding so some restriction could happen. We also should skip the intersection if
// we need to include transparent black pixels.
if (!fImage || !dstBounds.intersect(fLayerBounds)) {
return {nullptr, {}};
// TODO: This logic to skip a draw will also need to account for the tile mode, but we can
// always restrict to the intersection of dstBounds and the image's subset since we are
// currently always decal sampling.
// 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 (is_nearly_integer_translation(fTransform, &origin)) {
LayerSpace<SkIRect> imageBounds(SkIRect::MakeXYWH(origin.x(), origin.y(),
fImage->width(), fImage->height()));
if (!imageBounds.intersect(dstBounds)) {
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(), - origin.y(),
imageBounds.right() - origin.x(),
imageBounds.bottom() - origin.y() };
SkASSERT(subset.fLeft >= 0 && subset.fTop >= 0 &&
subset.fRight <= fImage->width() && subset.fBottom <= fImage->height());
return {fImage->makeSubset(subset), imageBounds.topLeft()};
} // else fall through and attempt a draw
sk_sp<SkSpecialSurface> surface = fImage->makeSurface(fImage->colorType(),
kPremul_SkAlphaType, {});
if (!surface) {
return {nullptr, {}};
SkCanvas* canvas = surface->getCanvas();
// GPU-backed special surfaces don't reset their contents.
canvas->translate(-dstBounds.left(),; // dst's origin adjustment
SkPaint paint;
// TODO: When using a tile mode other than kDecal, we'll need to use SkSpecialImage::asShader()
// and use drawRect(fLayerBounds).
if (!fLayerBounds.contains(dstBounds)) {
// We're resolving to a larger than necessary image, so make sure transparency outside of
// fLayerBounds is preserved.
// NOTE: This should only happen when the next layer requires processing transparent black.
canvas->concat(SkMatrix(fTransform)); // src's origin is embedded in fTransform
fImage->draw(canvas, 0.f, 0.f, fSamplingOptions, &paint);
return {surface->makeImageSnapshot(), dstBounds.topLeft()};
} // end namespace skif