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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 "include/core/SkMatrix.h"
#include "src/core/SkImageFilterTypes.h"
#include "src/core/SkImageFilter_Base.h"
#include "src/core/SkMatrixPriv.h"
// 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;
namespace skif {
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 matrix.mapRect(geom);
SkIRect Mapping::map<SkIRect>(const SkIRect& geom, const SkMatrix& matrix) {
SkRect mapped = matrix.mapRect(SkRect::Make(geom));
mapped.inset(1e-3f, 1e-3f);
return mapped.roundOut();
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);
FilterResult FilterResult::resolveToBounds(const LayerSpace<SkIRect>& newBounds) const {
// NOTE(michaelludwig) - This implementation is based on the assumption that an image resolved
// to 'newBounds' will be decal tiled and that the current image is decal tiled. Because of this
// simplification, the resolved image is always a subset of 'fImage' that matches the
// intersection of 'newBounds' and 'layerBounds()' so no rendering/copying is needed.
LayerSpace<SkIRect> tightBounds = newBounds;
if (!fImage || !tightBounds.intersect(this->layerBounds())) {
return {}; // Fully transparent
// Calculate offset from old origin to new origin, representing the relative subset in the image
LayerSpace<IVector> originShift = tightBounds.topLeft() - fOrigin;
auto subsetImage = fImage->makeSubset(SkIRect::MakeXYWH(originShift.x(), originShift.y(),
tightBounds.width(), tightBounds.height()));
return {std::move(subsetImage), tightBounds.topLeft()};
} // end namespace skif