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skia / skia / 97be28c4cc05231fe6e70dc32662c24700e731cc / . / src / shaders / gradients / SkGradientShaderBase.cpp
blob: 1d9677b09a2afe8b4d2088968b21f2fc725a888b [file] [log] [blame]
/*
* Copyright 2022 Google LLC
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "src/shaders/gradients/SkGradientShaderBase.h"
#include "include/core/SkColorSpace.h"
#include "include/private/base/SkVx.h"
#include "src/core/SkColorSpacePriv.h"
#include "src/core/SkColorSpaceXformSteps.h"
#include "src/core/SkConvertPixels.h"
#include "src/core/SkMatrixProvider.h"
#include "src/core/SkRasterPipeline.h"
#include "src/core/SkReadBuffer.h"
#include "src/core/SkVM.h"
#include "src/core/SkWriteBuffer.h"
#include <cmath>
enum GradientSerializationFlags {
// Bits 29:31 used for various boolean flags
kHasPosition_GSF = 0x80000000,
kHasLegacyLocalMatrix_GSF = 0x40000000,
kHasColorSpace_GSF = 0x20000000,
// Bits 12:28 unused
// Bits 8:11 for fTileMode
kTileModeShift_GSF = 8,
kTileModeMask_GSF = 0xF,
// Bits 4:7 for fInterpolation.fColorSpace
kInterpolationColorSpaceShift_GSF = 4,
kInterpolationColorSpaceMask_GSF = 0xF,
// Bits 1:3 for fInterpolation.fHueMethod
kInterpolationHueMethodShift_GSF = 1,
kInterpolationHueMethodMask_GSF = 0x7,
// Bit 0 for fInterpolation.fInPremul
kInterpolationInPremul_GSF = 0x1,
};
SkGradientShaderBase::Descriptor::Descriptor() {
sk_bzero(this, sizeof(*this));
fTileMode = SkTileMode::kClamp;
}
SkGradientShaderBase::Descriptor::~Descriptor() = default;
void SkGradientShaderBase::flatten(SkWriteBuffer& buffer) const {
uint32_t flags = 0;
if (fPositions) {
flags |= kHasPosition_GSF;
}
sk_sp<SkData> colorSpaceData = fColorSpace ? fColorSpace->serialize() : nullptr;
if (colorSpaceData) {
flags |= kHasColorSpace_GSF;
}
if (fInterpolation.fInPremul == Interpolation::InPremul::kYes) {
flags |= kInterpolationInPremul_GSF;
}
SkASSERT(static_cast<uint32_t>(fTileMode) <= kTileModeMask_GSF);
flags |= ((uint32_t)fTileMode << kTileModeShift_GSF);
SkASSERT(static_cast<uint32_t>(fInterpolation.fColorSpace) <= kInterpolationColorSpaceMask_GSF);
flags |= ((uint32_t)fInterpolation.fColorSpace << kInterpolationColorSpaceShift_GSF);
SkASSERT(static_cast<uint32_t>(fInterpolation.fHueMethod) <= kInterpolationHueMethodMask_GSF);
flags |= ((uint32_t)fInterpolation.fHueMethod << kInterpolationHueMethodShift_GSF);
buffer.writeUInt(flags);
// If we injected implicit first/last stops at construction time, omit those when serializing:
int colorCount = fColorCount;
const SkColor4f* colors = fColors;
const SkScalar* positions = fPositions;
if (fFirstStopIsImplicit) {
colorCount--;
colors++;
if (positions) {
positions++;
}
}
if (fLastStopIsImplicit) {
colorCount--;
}
buffer.writeColor4fArray(colors, colorCount);
if (colorSpaceData) {
buffer.writeDataAsByteArray(colorSpaceData.get());
}
if (positions) {
buffer.writeScalarArray(positions, colorCount);
}
}
template <int N, typename T, bool MEM_MOVE>
static bool validate_array(SkReadBuffer& buffer, size_t count, SkSTArray<N, T, MEM_MOVE>* array) {
if (!buffer.validateCanReadN<T>(count)) {
return false;
}
array->resize_back(count);
return true;
}
bool SkGradientShaderBase::DescriptorScope::unflatten(SkReadBuffer& buffer,
SkMatrix* legacyLocalMatrix) {
// New gradient format. Includes floating point color, color space, densely packed flags
uint32_t flags = buffer.readUInt();
fTileMode = (SkTileMode)((flags >> kTileModeShift_GSF) & kTileModeMask_GSF);
fInterpolation.fColorSpace = (Interpolation::ColorSpace)(
(flags >> kInterpolationColorSpaceShift_GSF) & kInterpolationColorSpaceMask_GSF);
fInterpolation.fHueMethod = (Interpolation::HueMethod)(
(flags >> kInterpolationHueMethodShift_GSF) & kInterpolationHueMethodMask_GSF);
fInterpolation.fInPremul = (flags & kInterpolationInPremul_GSF) ? Interpolation::InPremul::kYes
: Interpolation::InPremul::kNo;
fColorCount = buffer.getArrayCount();
if (!(validate_array(buffer, fColorCount, &fColorStorage) &&
buffer.readColor4fArray(fColorStorage.begin(), fColorCount))) {
return false;
}
fColors = fColorStorage.begin();
if (SkToBool(flags & kHasColorSpace_GSF)) {
sk_sp<SkData> data = buffer.readByteArrayAsData();
fColorSpace = data ? SkColorSpace::Deserialize(data->data(), data->size()) : nullptr;
} else {
fColorSpace = nullptr;
}
if (SkToBool(flags & kHasPosition_GSF)) {
if (!(validate_array(buffer, fColorCount, &fPositionStorage) &&
buffer.readScalarArray(fPositionStorage.begin(), fColorCount))) {
return false;
}
fPositions = fPositionStorage.begin();
} else {
fPositions = nullptr;
}
if (SkToBool(flags & kHasLegacyLocalMatrix_GSF)) {
SkASSERT(buffer.isVersionLT(SkPicturePriv::Version::kNoShaderLocalMatrix));
buffer.readMatrix(legacyLocalMatrix);
} else {
*legacyLocalMatrix = SkMatrix::I();
}
return buffer.isValid();
}
////////////////////////////////////////////////////////////////////////////////////////////
SkGradientShaderBase::SkGradientShaderBase(const Descriptor& desc, const SkMatrix& ptsToUnit)
: fPtsToUnit(ptsToUnit)
, fColorSpace(desc.fColorSpace ? desc.fColorSpace : SkColorSpace::MakeSRGB())
, fFirstStopIsImplicit(false)
, fLastStopIsImplicit(false)
, fColorsAreOpaque(true) {
fPtsToUnit.getType(); // Precache so reads are threadsafe.
SkASSERT(desc.fColorCount > 1);
fInterpolation = desc.fInterpolation;
SkASSERT((unsigned)desc.fTileMode < kSkTileModeCount);
fTileMode = desc.fTileMode;
/* Note: we let the caller skip the first and/or last position.
i.e. pos[0] = 0.3, pos[1] = 0.7
In these cases, we insert entries to ensure that the final data
will be bracketed by [0, 1].
i.e. our_pos[0] = 0, our_pos[1] = 0.3, our_pos[2] = 0.7, our_pos[3] = 1
Thus colorCount (the caller's value, and fColorCount (our value) may
differ by up to 2. In the above example:
colorCount = 2
fColorCount = 4
*/
fColorCount = desc.fColorCount;
// check if we need to add in start and/or end position/colors
if (desc.fPositions) {
fFirstStopIsImplicit = desc.fPositions[0] != 0;
fLastStopIsImplicit = desc.fPositions[desc.fColorCount - 1] != SK_Scalar1;
fColorCount += fFirstStopIsImplicit + fLastStopIsImplicit;
}
size_t storageSize =
fColorCount * (sizeof(SkColor4f) + (desc.fPositions ? sizeof(SkScalar) : 0));
fColors = reinterpret_cast<SkColor4f*>(fStorage.reset(storageSize));
fPositions = desc.fPositions ? reinterpret_cast<SkScalar*>(fColors + fColorCount) : nullptr;
// Now copy over the colors, adding the duplicates at t=0 and t=1 as needed
SkColor4f* colors = fColors;
if (fFirstStopIsImplicit) {
*colors++ = desc.fColors[0];
}
for (int i = 0; i < desc.fColorCount; ++i) {
colors[i] = desc.fColors[i];
fColorsAreOpaque = fColorsAreOpaque && (desc.fColors[i].fA == 1);
}
if (fLastStopIsImplicit) {
colors += desc.fColorCount;
*colors = desc.fColors[desc.fColorCount - 1];
}
if (desc.fPositions) {
SkScalar prev = 0;
SkScalar* positions = fPositions;
*positions++ = prev; // force the first pos to 0
int startIndex = fFirstStopIsImplicit ? 0 : 1;
int count = desc.fColorCount + fLastStopIsImplicit;
bool uniformStops = true;
const SkScalar uniformStep = desc.fPositions[startIndex] - prev;
for (int i = startIndex; i < count; i++) {
// Pin the last value to 1.0, and make sure pos is monotonic.
auto curr = (i == desc.fColorCount) ? 1 : SkTPin(desc.fPositions[i], prev, 1.0f);
uniformStops &= SkScalarNearlyEqual(uniformStep, curr - prev);
*positions++ = prev = curr;
}
// If the stops are uniform, treat them as implicit.
if (uniformStops) {
fPositions = nullptr;
}
}
}
SkGradientShaderBase::~SkGradientShaderBase() {}
static void add_stop_color(SkRasterPipeline_GradientCtx* ctx, size_t stop,
SkPMColor4f Fs, SkPMColor4f Bs) {
(ctx->fs[0])[stop] = Fs.fR;
(ctx->fs[1])[stop] = Fs.fG;
(ctx->fs[2])[stop] = Fs.fB;
(ctx->fs[3])[stop] = Fs.fA;
(ctx->bs[0])[stop] = Bs.fR;
(ctx->bs[1])[stop] = Bs.fG;
(ctx->bs[2])[stop] = Bs.fB;
(ctx->bs[3])[stop] = Bs.fA;
}
static void add_const_color(SkRasterPipeline_GradientCtx* ctx, size_t stop, SkPMColor4f color) {
add_stop_color(ctx, stop, { 0, 0, 0, 0 }, color);
}
// Calculate a factor F and a bias B so that color = F*t + B when t is in range of
// the stop. Assume that the distance between stops is 1/gapCount.
static void init_stop_evenly(SkRasterPipeline_GradientCtx* ctx, float gapCount, size_t stop,
SkPMColor4f c_l, SkPMColor4f c_r) {
// Clankium's GCC 4.9 targeting ARMv7 is barfing when we use Sk4f math here, so go scalar...
SkPMColor4f Fs = {
(c_r.fR - c_l.fR) * gapCount,
(c_r.fG - c_l.fG) * gapCount,
(c_r.fB - c_l.fB) * gapCount,
(c_r.fA - c_l.fA) * gapCount,
};
SkPMColor4f Bs = {
c_l.fR - Fs.fR*(stop/gapCount),
c_l.fG - Fs.fG*(stop/gapCount),
c_l.fB - Fs.fB*(stop/gapCount),
c_l.fA - Fs.fA*(stop/gapCount),
};
add_stop_color(ctx, stop, Fs, Bs);
}
// For each stop we calculate a bias B and a scale factor F, such that
// for any t between stops n and n+1, the color we want is B[n] + F[n]*t.
static void init_stop_pos(SkRasterPipeline_GradientCtx* ctx, size_t stop, float t_l, float t_r,
SkPMColor4f c_l, SkPMColor4f c_r) {
// See note about Clankium's old compiler in init_stop_evenly().
SkPMColor4f Fs = {
(c_r.fR - c_l.fR) / (t_r - t_l),
(c_r.fG - c_l.fG) / (t_r - t_l),
(c_r.fB - c_l.fB) / (t_r - t_l),
(c_r.fA - c_l.fA) / (t_r - t_l),
};
SkPMColor4f Bs = {
c_l.fR - Fs.fR*t_l,
c_l.fG - Fs.fG*t_l,
c_l.fB - Fs.fB*t_l,
c_l.fA - Fs.fA*t_l,
};
ctx->ts[stop] = t_l;
add_stop_color(ctx, stop, Fs, Bs);
}
void SkGradientShaderBase::AppendGradientFillStages(SkRasterPipeline* p,
SkArenaAlloc* alloc,
const SkPMColor4f* pmColors,
const SkScalar* positions,
int count) {
// The two-stop case with stops at 0 and 1.
if (count == 2 && positions == nullptr) {
const SkPMColor4f c_l = pmColors[0],
c_r = pmColors[1];
// See F and B below.
auto ctx = alloc->make<SkRasterPipeline_EvenlySpaced2StopGradientCtx>();
(skvx::float4::Load(c_r.vec()) - skvx::float4::Load(c_l.vec())).store(ctx->f);
( skvx::float4::Load(c_l.vec())).store(ctx->b);
p->append(SkRasterPipelineOp::evenly_spaced_2_stop_gradient, ctx);
} else {
auto* ctx = alloc->make<SkRasterPipeline_GradientCtx>();
// Note: In order to handle clamps in search, the search assumes a stop conceptully placed
// at -inf. Therefore, the max number of stops is fColorCount+1.
for (int i = 0; i < 4; i++) {
// Allocate at least at for the AVX2 gather from a YMM register.
ctx->fs[i] = alloc->makeArray<float>(std::max(count + 1, 8));
ctx->bs[i] = alloc->makeArray<float>(std::max(count + 1, 8));
}
if (positions == nullptr) {
// Handle evenly distributed stops.
size_t stopCount = count;
float gapCount = stopCount - 1;
SkPMColor4f c_l = pmColors[0];
for (size_t i = 0; i < stopCount - 1; i++) {
SkPMColor4f c_r = pmColors[i + 1];
init_stop_evenly(ctx, gapCount, i, c_l, c_r);
c_l = c_r;
}
add_const_color(ctx, stopCount - 1, c_l);
ctx->stopCount = stopCount;
p->append(SkRasterPipelineOp::evenly_spaced_gradient, ctx);
} else {
// Handle arbitrary stops.
ctx->ts = alloc->makeArray<float>(count + 1);
// Remove the default stops inserted by SkGradientShaderBase::SkGradientShaderBase
// because they are naturally handled by the search method.
int firstStop;
int lastStop;
if (count > 2) {
firstStop = pmColors[0] != pmColors[1] ? 0 : 1;
lastStop = pmColors[count - 2] != pmColors[count - 1] ? count - 1 : count - 2;
} else {
firstStop = 0;
lastStop = 1;
}
size_t stopCount = 0;
float t_l = positions[firstStop];
SkPMColor4f c_l = pmColors[firstStop];
add_const_color(ctx, stopCount++, c_l);
// N.B. lastStop is the index of the last stop, not one after.
for (int i = firstStop; i < lastStop; i++) {
float t_r = positions[i + 1];
SkPMColor4f c_r = pmColors[i + 1];
SkASSERT(t_l <= t_r);
if (t_l < t_r) {
init_stop_pos(ctx, stopCount, t_l, t_r, c_l, c_r);
stopCount += 1;
}
t_l = t_r;
c_l = c_r;
}
ctx->ts[stopCount] = t_l;
add_const_color(ctx, stopCount++, c_l);
ctx->stopCount = stopCount;
p->append(SkRasterPipelineOp::gradient, ctx);
}
}
}
bool SkGradientShaderBase::appendStages(const SkStageRec& rec, const MatrixRec& mRec) const {
SkRasterPipeline* p = rec.fPipeline;
SkArenaAlloc* alloc = rec.fAlloc;
SkRasterPipeline_DecalTileCtx* decal_ctx = nullptr;
std::optional<MatrixRec> newMRec = mRec.apply(rec, fPtsToUnit);
if (!newMRec.has_value()) {
return false;
}
SkRasterPipeline_<256> postPipeline;
this->appendGradientStages(alloc, p, &postPipeline);
switch(fTileMode) {
case SkTileMode::kMirror: p->append(SkRasterPipelineOp::mirror_x_1); break;
case SkTileMode::kRepeat: p->append(SkRasterPipelineOp::repeat_x_1); break;
case SkTileMode::kDecal:
decal_ctx = alloc->make<SkRasterPipeline_DecalTileCtx>();
decal_ctx->limit_x = SkBits2Float(SkFloat2Bits(1.0f) + 1);
// reuse mask + limit_x stage, or create a custom decal_1 that just stores the mask
p->append(SkRasterPipelineOp::decal_x, decal_ctx);
[[fallthrough]];
case SkTileMode::kClamp:
if (!fPositions) {
// We clamp only when the stops are evenly spaced.
// If not, there may be hard stops, and clamping ruins hard stops at 0 and/or 1.
// In that case, we must make sure we're using the general "gradient" stage,
// which is the only stage that will correctly handle unclamped t.
p->append(SkRasterPipelineOp::clamp_x_1);
}
break;
}
// Transform all of the colors to destination color space, possibly premultiplied
SkColor4fXformer xformedColors(this, rec.fDstCS);
AppendGradientFillStages(p, alloc, xformedColors.fColors.begin(), fPositions, fColorCount);
using ColorSpace = Interpolation::ColorSpace;
bool colorIsPremul = this->interpolateInPremul();
// If we interpolated premul colors in any of the special color spaces, we need to unpremul
if (colorIsPremul && !fColorsAreOpaque) {
switch (fInterpolation.fColorSpace) {
case ColorSpace::kLab:
case ColorSpace::kOKLab:
p->append(SkRasterPipelineOp::unpremul);
colorIsPremul = false;
break;
case ColorSpace::kLCH:
case ColorSpace::kOKLCH:
case ColorSpace::kHSL:
case ColorSpace::kHWB:
p->append(SkRasterPipelineOp::unpremul_polar);
colorIsPremul = false;
break;
default: break;
}
}
// Convert colors in exotic spaces back to their intermediate SkColorSpace
switch (fInterpolation.fColorSpace) {
case ColorSpace::kLab: p->append(SkRasterPipelineOp::css_lab_to_xyz); break;
case ColorSpace::kOKLab: p->append(SkRasterPipelineOp::css_oklab_to_linear_srgb); break;
case ColorSpace::kLCH: p->append(SkRasterPipelineOp::css_hcl_to_lab);
p->append(SkRasterPipelineOp::css_lab_to_xyz); break;
case ColorSpace::kOKLCH: p->append(SkRasterPipelineOp::css_hcl_to_lab);
p->append(SkRasterPipelineOp::css_oklab_to_linear_srgb); break;
case ColorSpace::kHSL: p->append(SkRasterPipelineOp::css_hsl_to_srgb); break;
case ColorSpace::kHWB: p->append(SkRasterPipelineOp::css_hwb_to_srgb); break;
default: break;
}
// Now transform from intermediate to destination color space.
// See comments in GrGradientShader.cpp about the decisions here.
SkColorSpace* dstColorSpace = rec.fDstCS ? rec.fDstCS : sk_srgb_singleton();
SkAlphaType intermediateAlphaType = colorIsPremul ? kPremul_SkAlphaType : kUnpremul_SkAlphaType;
// TODO(skia:13108): Get dst alpha type correctly
SkAlphaType dstAlphaType = kPremul_SkAlphaType;
if (fColorsAreOpaque) {
intermediateAlphaType = dstAlphaType = kUnpremul_SkAlphaType;
}
alloc->make<SkColorSpaceXformSteps>(xformedColors.fIntermediateColorSpace.get(),
intermediateAlphaType,
dstColorSpace,
dstAlphaType)
->apply(p);
if (decal_ctx) {
p->append(SkRasterPipelineOp::check_decal_mask, decal_ctx);
}
p->extend(postPipeline);
return true;
}
// Color conversion functions used in gradient interpolation, based on
// https://www.w3.org/TR/css-color-4/#color-conversion-code
static skvm::Color css_lab_to_xyz(skvm::Color lab) {
constexpr float k = 24389 / 27.0f;
constexpr float e = 216 / 24389.0f;
skvm::F32 f[3];
f[1] = (lab.r + 16) * (1 / 116.0f);
f[0] = (lab.g * (1 / 500.0f)) + f[1];
f[2] = f[1] - (lab.b * (1 / 200.0f));
skvm::F32 f_cubed[3] = { f[0]*f[0]*f[0], f[1]*f[1]*f[1], f[2]*f[2]*f[2] };
skvm::F32 xyz[3] = {
skvm::select(f_cubed[0] > e, f_cubed[0], (116 * f[0] - 16) * (1 / k)),
skvm::select(lab.r > k * e , f_cubed[1], lab.r * (1 / k)),
skvm::select(f_cubed[2] > e, f_cubed[2], (116 * f[2] - 16) * (1 / k))
};
constexpr float D50[3] = { 0.3457f / 0.3585f, 1.0f, (1.0f - 0.3457f - 0.3585f) / 0.3585f };
return skvm::Color { xyz[0]*D50[0], xyz[1]*D50[1], xyz[2]*D50[2], lab.a };
}
// Skia stores all polar colors with hue in the first component, so this "LCH -> Lab" transform
// actually takes "HCL". This is also used to do the same polar transform for OkHCL to OkLAB.
static skvm::Color css_hcl_to_lab(skvm::Color hcl) {
skvm::F32 hueRadians = hcl.r * (SK_FloatPI / 180);
return skvm::Color {
hcl.b,
hcl.g * approx_cos(hueRadians),
hcl.g * approx_sin(hueRadians),
hcl.a
};
}
static skvm::Color css_hcl_to_xyz(skvm::Color hcl) {
return css_lab_to_xyz(css_hcl_to_lab(hcl));
}
static skvm::Color css_oklab_to_linear_srgb(skvm::Color oklab) {
skvm::F32 l_ = oklab.r + 0.3963377774f * oklab.g + 0.2158037573f * oklab.b,
m_ = oklab.r - 0.1055613458f * oklab.g - 0.0638541728f * oklab.b,
s_ = oklab.r - 0.0894841775f * oklab.g - 1.2914855480f * oklab.b;
skvm::F32 l = l_*l_*l_,
m = m_*m_*m_,
s = s_*s_*s_;
return skvm::Color {
+4.0767416621f * l - 3.3077115913f * m + 0.2309699292f * s,
-1.2684380046f * l + 2.6097574011f * m - 0.3413193965f * s,
-0.0041960863f * l - 0.7034186147f * m + 1.7076147010f * s,
oklab.a
};
}
static skvm::Color css_okhcl_to_linear_srgb(skvm::Color okhcl) {
return css_oklab_to_linear_srgb(css_hcl_to_lab(okhcl));
}
static skvm::F32 mod_f(skvm::F32 x, float y) {
return x - y * skvm::floor(x * (1 / y));
}
static skvm::Color css_hsl_to_srgb(skvm::Color hsl) {
hsl.r = mod_f(hsl.r, 360);
hsl.r = skvm::select(hsl.r < 0, hsl.r + 360, hsl.r);
hsl.g *= 0.01f;
hsl.b *= 0.01f;
skvm::F32 k[3] = {
mod_f(0 + hsl.r * (1 / 30.0f), 12),
mod_f(8 + hsl.r * (1 / 30.0f), 12),
mod_f(4 + hsl.r * (1 / 30.0f), 12),
};
skvm::F32 a = hsl.g * min(hsl.b, 1 - hsl.b);
return skvm::Color {
hsl.b - a * clamp(min(k[0] - 3, 9 - k[0]), -1, 1),
hsl.b - a * clamp(min(k[1] - 3, 9 - k[1]), -1, 1),
hsl.b - a * clamp(min(k[2] - 3, 9 - k[2]), -1, 1),
hsl.a
};
}
static skvm::Color css_hwb_to_srgb(skvm::Color hwb, skvm::Builder* p) {
hwb.g *= 0.01f;
hwb.b *= 0.01f;
skvm::F32 gray = hwb.g / (hwb.g + hwb.b);
skvm::Color rgb = css_hsl_to_srgb(skvm::Color{hwb.r, p->splat(100.0f), p->splat(50.0f), hwb.a});
rgb.r = rgb.r * (1 - hwb.g - hwb.b) + hwb.g;
rgb.g = rgb.g * (1 - hwb.g - hwb.b) + hwb.g;
rgb.b = rgb.b * (1 - hwb.g - hwb.b) + hwb.g;
skvm::I32 isGray = (hwb.g + hwb.b) >= 1;
return skvm::Color {
select(isGray, gray, rgb.r),
select(isGray, gray, rgb.g),
select(isGray, gray, rgb.b),
hwb.a
};
}
skvm::Color SkGradientShaderBase::onProgram(skvm::Builder* p,
skvm::Coord device, skvm::Coord local,
skvm::Color /*paint*/,
const SkMatrixProvider& mats, const SkMatrix* localM,
const SkColorInfo& dstInfo,
skvm::Uniforms* uniforms, SkArenaAlloc* alloc) const {
SkMatrix inv;
if (!this->computeTotalInverse(mats.localToDevice(), localM, &inv)) {
return {};
}
inv.postConcat(fPtsToUnit);
inv.normalizePerspective();
local = SkShaderBase::ApplyMatrix(p, inv, local, uniforms);
skvm::I32 mask = p->splat(~0);
skvm::F32 t = this->transformT(p,uniforms, local, &mask);
// Perhaps unexpectedly, clamping is handled naturally by our search, so we
// don't explicitly clamp t to [0,1]. That clamp would break hard stops
// right at 0 or 1 boundaries in kClamp mode. (kRepeat and kMirror always
// produce values in [0,1].)
switch(fTileMode) {
case SkTileMode::kClamp:
break;
case SkTileMode::kDecal:
mask &= (t == clamp01(t));
break;
case SkTileMode::kRepeat:
t = fract(t);
break;
case SkTileMode::kMirror: {
// t = | (t-1) - 2*(floor( (t-1)*0.5 )) - 1 |
// {-A-} {--------B-------}
skvm::F32 A = t - 1.0f,
B = floor(A * 0.5f);
t = abs(A - (B + B) - 1.0f);
} break;
}
// Transform our colors as we want them interpolated, in dst color space, possibly premul.
SkColor4fXformer xformedColors(this, dstInfo.colorSpace());
const SkPMColor4f* rgba = xformedColors.fColors.begin();
// Transform our colors into a scale factor f and bias b such that for
// any t between stops i and i+1, the color we want is mad(t, f[i], b[i]).
using F4 = skvx::Vec<4,float>;
struct FB { F4 f,b; };
skvm::Color color;
auto uniformF = [&](float x) { return p->uniformF(uniforms->pushF(x)); };
if (fColorCount == 2) {
// 2-stop gradients have colors at 0 and 1, and so must be evenly spaced.
SkASSERT(fPositions == nullptr);
// With 2 stops, we upload the single FB as uniforms and interpolate directly with t.
F4 lo = F4::Load(rgba + 0),
hi = F4::Load(rgba + 1);
F4 F = hi - lo,
B = lo;
auto T = clamp01(t);
color = {
T * uniformF(F[0]) + uniformF(B[0]),
T * uniformF(F[1]) + uniformF(B[1]),
T * uniformF(F[2]) + uniformF(B[2]),
T * uniformF(F[3]) + uniformF(B[3]),
};
} else {
// To handle clamps in search we add a conceptual stop at t=-inf, so we
// may need up to fColorCount+1 FBs and fColorCount t stops between them:
//
// FBs: [color 0] [color 0->1] [color 1->2] [color 2->3] ...
// stops: (-inf) t0 t1 t2 ...
//
// Both these arrays could end up shorter if any hard stops share the same t.
FB* fb = alloc->makeArrayDefault<FB>(fColorCount+1);
std::vector<float> stops; // TODO: SkSTArray?
stops.reserve(fColorCount);
// Here's our conceptual stop at t=-inf covering all t<=0, clamping to our first color.
float t_lo = this->getPos(0);
F4 color_lo = F4::Load(rgba);
fb[0] = { 0.0f, color_lo };
// N.B. No stops[] entry for this implicit -inf.
// Now the non-edge cases, calculating scale and bias between adjacent normal stops.
for (int i = 1; i < fColorCount; i++) {
float t_hi = this->getPos(i);
F4 color_hi = F4::Load(rgba + i);
// If t_lo == t_hi, we're on a hard stop, and transition immediately to the next color.
SkASSERT(t_lo <= t_hi);
if (t_lo < t_hi) {
F4 f = (color_hi - color_lo) / (t_hi - t_lo),
b = color_lo - f*t_lo;
stops.push_back(t_lo);
fb[stops.size()] = {f,b};
}
t_lo = t_hi;
color_lo = color_hi;
}
// Anything >= our final t clamps to our final color.
stops.push_back(t_lo);
fb[stops.size()] = { 0.0f, color_lo };
// We'll gather FBs from that array we just created.
skvm::Uniform fbs = uniforms->pushPtr(fb);
// Find the two stops we need to interpolate.
skvm::I32 ix;
if (fPositions == nullptr) {
// Evenly spaced stops... we can calculate ix directly.
ix = trunc(clamp(t * uniformF(stops.size() - 1) + 1.0f, 0.0f, uniformF(stops.size())));
} else {
// Starting ix at 0 bakes in our conceptual first stop at -inf.
// TODO: good place to experiment with a loop in skvm.... stops.size() can be huge.
ix = p->splat(0);
for (float stop : stops) {
// ix += (t >= stop) ? +1 : 0 ~~>
// ix -= (t >= stop) ? -1 : 0
ix -= (t >= uniformF(stop));
}
// TODO: we could skip any of the default stops GradientShaderBase's ctor added
// to ensure the full [0,1] span is covered. This linear search doesn't need
// them for correctness, and it'd be up to two fewer stops to check.
// N.B. we do still need those stops for the fPositions == nullptr direct math path.
}
// A scale factor and bias for each lane, 8 total.
// TODO: simpler, faster, tidier to push 8 uniform pointers, one for each struct lane?
ix = shl(ix, 3);
skvm::F32 Fr = gatherF(fbs, ix + 0);
skvm::F32 Fg = gatherF(fbs, ix + 1);
skvm::F32 Fb = gatherF(fbs, ix + 2);
skvm::F32 Fa = gatherF(fbs, ix + 3);
skvm::F32 Br = gatherF(fbs, ix + 4);
skvm::F32 Bg = gatherF(fbs, ix + 5);
skvm::F32 Bb = gatherF(fbs, ix + 6);
skvm::F32 Ba = gatherF(fbs, ix + 7);
// This is what we've been building towards!
color = {
t * Fr + Br,
t * Fg + Bg,
t * Fb + Bb,
t * Fa + Ba,
};
}
using ColorSpace = Interpolation::ColorSpace;
bool colorIsPremul = this->interpolateInPremul();
// If we interpolated premul colors in any of the special color spaces, we need to unpremul
if (colorIsPremul) {
switch (fInterpolation.fColorSpace) {
case ColorSpace::kLab:
case ColorSpace::kOKLab:
color = unpremul(color);
colorIsPremul = false;
break;
case ColorSpace::kLCH:
case ColorSpace::kOKLCH:
case ColorSpace::kHSL:
case ColorSpace::kHWB: {
// Avoid unpremuling hue
skvm::F32 hue = color.r;
color = unpremul(color);
color.r = hue;
colorIsPremul = false;
} break;
default: break;
}
}
// Convert colors in exotic spaces back to their intermediate SkColorSpace
switch (fInterpolation.fColorSpace) {
case ColorSpace::kLab: color = css_lab_to_xyz(color); break;
case ColorSpace::kOKLab: color = css_oklab_to_linear_srgb(color); break;
case ColorSpace::kLCH: color = css_hcl_to_xyz(color); break;
case ColorSpace::kOKLCH: color = css_okhcl_to_linear_srgb(color); break;
case ColorSpace::kHSL: color = css_hsl_to_srgb(color); break;
case ColorSpace::kHWB: color = css_hwb_to_srgb(color, p); break;
default: break;
}
// Now transform from intermediate to destination color space.
// See comments in GrGradientShader.cpp about the decisions here.
SkColorSpace* dstColorSpace = dstInfo.colorSpace() ? dstInfo.colorSpace() : sk_srgb_singleton();
SkAlphaType intermediateAlphaType = colorIsPremul ? kPremul_SkAlphaType : kUnpremul_SkAlphaType;
SkAlphaType dstAlphaType = dstInfo.alphaType();
if (fColorsAreOpaque) {
intermediateAlphaType = dstAlphaType = kUnpremul_SkAlphaType;
}
color = SkColorSpaceXformSteps{xformedColors.fIntermediateColorSpace.get(),
intermediateAlphaType,
dstColorSpace,
dstAlphaType}
.program(p, uniforms, color);
return {
pun_to_F32(mask & pun_to_I32(color.r)),
pun_to_F32(mask & pun_to_I32(color.g)),
pun_to_F32(mask & pun_to_I32(color.b)),
pun_to_F32(mask & pun_to_I32(color.a)),
};
}
bool SkGradientShaderBase::isOpaque() const {
return fColorsAreOpaque && (this->getTileMode() != SkTileMode::kDecal);
}
static unsigned rounded_divide(unsigned numer, unsigned denom) {
return (numer + (denom >> 1)) / denom;
}
bool SkGradientShaderBase::onAsLuminanceColor(SkColor* lum) const {
// we just compute an average color.
// possibly we could weight this based on the proportional width for each color
// assuming they are not evenly distributed in the fPos array.
int r = 0;
int g = 0;
int b = 0;
const int n = fColorCount;
// TODO: use linear colors?
for (int i = 0; i < n; ++i) {
SkColor c = this->getLegacyColor(i);
r += SkColorGetR(c);
g += SkColorGetG(c);
b += SkColorGetB(c);
}
*lum = SkColorSetRGB(rounded_divide(r, n), rounded_divide(g, n), rounded_divide(b, n));
return true;
}
static sk_sp<SkColorSpace> intermediate_color_space(SkGradientShader::Interpolation::ColorSpace cs,
SkColorSpace* dst) {
using ColorSpace = SkGradientShader::Interpolation::ColorSpace;
switch (cs) {
case ColorSpace::kDestination: return sk_ref_sp(dst);
// css-color-4 allows XYZD50 and XYZD65. For gradients, those are redundant. Interpolating
// in any linear RGB space, (regardless of white point), gives the same answer.
case ColorSpace::kSRGBLinear: return SkColorSpace::MakeSRGBLinear();
case ColorSpace::kSRGB:
case ColorSpace::kHSL:
case ColorSpace::kHWB: return SkColorSpace::MakeSRGB();
case ColorSpace::kLab:
case ColorSpace::kLCH:
// Conversion to Lab (and LCH) starts with XYZD50
return SkColorSpace::MakeRGB(SkNamedTransferFn::kLinear, SkNamedGamut::kXYZ);
case ColorSpace::kOKLab:
case ColorSpace::kOKLCH:
// The "standard" conversion to these spaces starts with XYZD65. That requires extra
// effort to conjure. The author also has reference code for going directly from linear
// sRGB, so we use that.
// TODO(skia:13108): Even better would be to have an LMS color space, because the first
// part of the conversion is a matrix multiply, which could be absorbed into the
// color space xform.
return SkColorSpace::MakeSRGBLinear();
}
SkUNREACHABLE;
}
typedef SkPMColor4f (*ConvertColorProc)(SkPMColor4f);
static SkPMColor4f srgb_to_hsl(SkPMColor4f rgb) {
float mx = std::max({rgb.fR, rgb.fG, rgb.fB});
float mn = std::min({rgb.fR, rgb.fG, rgb.fB});
float hue = 0, sat = 0, light = (mn + mx) / 2;
float d = mx - mn;
if (d != 0) {
sat = (light == 0 || light == 1) ? 0 : (mx - light) / std::min(light, 1 - light);
if (mx == rgb.fR) {
hue = (rgb.fG - rgb.fB) / d + (rgb.fG < rgb.fB ? 6 : 0);
} else if (mx == rgb.fG) {
hue = (rgb.fB - rgb.fR) / d + 2;
} else {
hue = (rgb.fR - rgb.fG) / d + 4;
}
hue *= 60;
}
return { hue, sat * 100, light * 100, rgb.fA };
}
static SkPMColor4f srgb_to_hwb(SkPMColor4f rgb) {
SkPMColor4f hsl = srgb_to_hsl(rgb);
float white = std::min({rgb.fR, rgb.fG, rgb.fB});
float black = 1 - std::max({rgb.fR, rgb.fG, rgb.fB});
return { hsl.fR, white * 100, black * 100, rgb.fA };
}
static SkPMColor4f xyzd50_to_lab(SkPMColor4f xyz) {
constexpr float D50[3] = { 0.3457f / 0.3585f, 1.0f, (1.0f - 0.3457f - 0.3585f) / 0.3585f };
constexpr float e = 216.0f / 24389;
constexpr float k = 24389.0f / 27;
SkPMColor4f f;
for (int i = 0; i < 3; ++i) {
float v = xyz[i] / D50[i];
f[i] = (v > e) ? std::cbrtf(v) : (k * v + 16) / 116;
}
return { (116 * f[1]) - 16, 500 * (f[0] - f[1]), 200 * (f[1] - f[2]), xyz.fA };
}
// The color space is technically LCH, but we produce HCL, so that all polar spaces have hue in the
// first component. This simplifies the hue handling for HueMethod and premul/unpremul.
static SkPMColor4f xyzd50_to_hcl(SkPMColor4f xyz) {
SkPMColor4f Lab = xyzd50_to_lab(xyz);
float hue = sk_float_radians_to_degrees(atan2f(Lab[2], Lab[1]));
return {hue >= 0 ? hue : hue + 360,
sqrtf(Lab[1] * Lab[1] + Lab[2] * Lab[2]),
Lab[0],
xyz.fA};
}
// https://bottosson.github.io/posts/oklab/#converting-from-linear-srgb-to-oklab
static SkPMColor4f lin_srgb_to_oklab(SkPMColor4f rgb) {
float l = 0.4122214708f * rgb.fR + 0.5363325363f * rgb.fG + 0.0514459929f * rgb.fB;
float m = 0.2119034982f * rgb.fR + 0.6806995451f * rgb.fG + 0.1073969566f * rgb.fB;
float s = 0.0883024619f * rgb.fR + 0.2817188376f * rgb.fG + 0.6299787005f * rgb.fB;
l = std::cbrtf(l);
m = std::cbrtf(m);
s = std::cbrtf(s);
return {
0.2104542553f*l + 0.7936177850f*m - 0.0040720468f*s,
1.9779984951f*l - 2.4285922050f*m + 0.4505937099f*s,
0.0259040371f*l + 0.7827717662f*m - 0.8086757660f*s,
rgb.fA
};
}
// The color space is technically OkLCH, but we produce HCL, so that all polar spaces have hue in
// the first component. This simplifies the hue handling for HueMethod and premul/unpremul.
static SkPMColor4f lin_srgb_to_okhcl(SkPMColor4f rgb) {
SkPMColor4f OKLab = lin_srgb_to_oklab(rgb);
float hue = sk_float_radians_to_degrees(atan2f(OKLab[2], OKLab[1]));
return {hue >= 0 ? hue : hue + 360,
sqrtf(OKLab[1] * OKLab[1] + OKLab[2] * OKLab[2]),
OKLab[0],
rgb.fA};
}
static SkPMColor4f premul_polar(SkPMColor4f hsl) {
return { hsl.fR, hsl.fG * hsl.fA, hsl.fB * hsl.fA, hsl.fA };
}
static SkPMColor4f premul_rgb(SkPMColor4f rgb) {
return { rgb.fR * rgb.fA, rgb.fG * rgb.fA, rgb.fB * rgb.fA, rgb.fA };
}
static bool color_space_is_polar(SkGradientShader::Interpolation::ColorSpace cs) {
using ColorSpace = SkGradientShader::Interpolation::ColorSpace;
switch (cs) {
case ColorSpace::kLCH:
case ColorSpace::kOKLCH:
case ColorSpace::kHSL:
case ColorSpace::kHWB:
return true;
default:
return false;
}
}
// Given `colors` in `src` color space, an interpolation space, and a `dst` color space,
// we are doing several things. First, some definitions:
//
// The interpolation color space is "special" if it can't be represented as an SkColorSpace. This
// applies to any color space that isn't an RGB space, like Lab or HSL. These need special handling
// because we have to run bespoke code to do the conversion (before interpolation here, and after
// interpolation in the backend shader/pipeline).
//
// The interpolation color space is "polar" if it involves hue (HSL, HWB, LCH, Oklch). These need
// special handling, becuase hue is never premultiplied, and because HueMethod comes into play.
//
// 1) Pick an `intermediate` SkColorSpace. If the interpolation color space is not "special",
// (kDestination, kSRGB, etc... ), then `intermediate` is exact. Otherwise, `intermediate` is the
// RGB space that prepares us to do the final conversion. For example, conversion to Lab starts
// with XYZD50, so `intermediate` will be XYZD50 if we're actually interpolating in Lab.
// 2) Transform all colors to the `intermediate` color space, leaving them unpremultiplied.
// 3) If the interpolation color space is "special", transform the colors to that space.
// 4) If the interpolation color space is "polar", adjust the angles to respect HueMethod.
// 5) If premul interpolation is requested, apply that. For "polar" interpolated colors, don't
// premultiply hue, only the other two channels. Note that there are four polar spaces.
// Two have hue as the first component, and two have it as the third component. To reduce
// complexity, we always store hue in the first component, swapping it with luminance for
// LCH and Oklch. The backend code (eg, shaders) needs to know about this.
SkColor4fXformer::SkColor4fXformer(const SkGradientShaderBase* shader, SkColorSpace* dst) {
using ColorSpace = SkGradientShader::Interpolation::ColorSpace;
using HueMethod = SkGradientShader::Interpolation::HueMethod;
const int colorCount = shader->fColorCount;
const SkGradientShader::Interpolation interpolation = shader->fInterpolation;
// 1) Determine the color space of our intermediate colors
fIntermediateColorSpace = intermediate_color_space(interpolation.fColorSpace, dst);
// 2) Convert all colors to the intermediate color space
auto info = SkImageInfo::Make(colorCount, 1, kRGBA_F32_SkColorType, kUnpremul_SkAlphaType);
auto dstInfo = info.makeColorSpace(fIntermediateColorSpace);
auto srcInfo = info.makeColorSpace(shader->fColorSpace);
fColors.reset(colorCount);
SkAssertResult(SkConvertPixels(dstInfo, fColors.begin(), info.minRowBytes(),
srcInfo, shader->fColors, info.minRowBytes()));
// 3) Transform to the interpolation color space (if it's special)
ConvertColorProc convertFn = nullptr;
switch (interpolation.fColorSpace) {
case ColorSpace::kHSL: convertFn = srgb_to_hsl; break;
case ColorSpace::kHWB: convertFn = srgb_to_hwb; break;
case ColorSpace::kLab: convertFn = xyzd50_to_lab; break;
case ColorSpace::kLCH: convertFn = xyzd50_to_hcl; break;
case ColorSpace::kOKLab: convertFn = lin_srgb_to_oklab; break;
case ColorSpace::kOKLCH: convertFn = lin_srgb_to_okhcl; break;
default: break;
}
if (convertFn) {
for (int i = 0; i < colorCount; ++i) {
fColors[i] = convertFn(fColors[i]);
}
}
// 4) For polar colors, adjust hue values to respect the hue method. We're using a trick here...
// The specification looks at adjacent colors, and adjusts one or the other. Because we store
// the stops in uniforms (and our backend conversions normalize the hue angle), we can
// instead always apply the adjustment to the *second* color. That lets us keep a running
// total, and do a single pass across all the colors to respect the requested hue method,
// without needing to do any extra work per-pixel.
if (color_space_is_polar(interpolation.fColorSpace)) {
float delta = 0;
for (int i = 0; i < colorCount - 1; ++i) {
float h1 = fColors[i].fR;
float& h2 = fColors[i+1].fR;
h2 += delta;
switch (interpolation.fHueMethod) {
case HueMethod::kShorter:
if (h2 - h1 > 180) {
h2 -= 360; // i.e. h1 += 360
delta -= 360;
} else if (h2 - h1 < -180) {
h2 += 360;
delta += 360;
}
break;
case HueMethod::kLonger:
if ((i == 0 && shader->fFirstStopIsImplicit) ||
(i == colorCount - 2 && shader->fLastStopIsImplicit)) {
// Do nothing. We don't want to introduce a full revolution for these stops
// Full rationale at skbug.com/13941
} else if (0 < h2 - h1 && h2 - h1 < 180) {
h2 -= 360; // i.e. h1 += 360
delta -= 360;
} else if (-180 < h2 - h1 && h2 - h1 <= 0) {
h2 += 360;
delta += 360;
}
break;
case HueMethod::kIncreasing:
if (h2 < h1) {
h2 += 360;
delta += 360;
}
break;
case HueMethod::kDecreasing:
if (h1 < h2) {
h2 -= 360; // i.e. h1 += 360;
delta -= 360;
}
break;
}
}
}
// 5) Apply premultiplication
ConvertColorProc premulFn = nullptr;
if (static_cast<bool>(interpolation.fInPremul)) {
switch (interpolation.fColorSpace) {
case ColorSpace::kHSL:
case ColorSpace::kHWB:
case ColorSpace::kLCH:
case ColorSpace::kOKLCH: premulFn = premul_polar; break;
default: premulFn = premul_rgb; break;
}
}
if (premulFn) {
for (int i = 0; i < colorCount; ++i) {
fColors[i] = premulFn(fColors[i]);
}
}
}
SkColorConverter::SkColorConverter(const SkColor* colors, int count) {
const float ONE_OVER_255 = 1.f / 255;
for (int i = 0; i < count; ++i) {
fColors4f.push_back({ SkColorGetR(colors[i]) * ONE_OVER_255,
SkColorGetG(colors[i]) * ONE_OVER_255,
SkColorGetB(colors[i]) * ONE_OVER_255,
SkColorGetA(colors[i]) * ONE_OVER_255 });
}
}
void SkGradientShaderBase::commonAsAGradient(GradientInfo* info) const {
if (info) {
if (info->fColorCount >= fColorCount) {
if (info->fColors) {
for (int i = 0; i < fColorCount; ++i) {
info->fColors[i] = this->getLegacyColor(i);
}
}
if (info->fColorOffsets) {
for (int i = 0; i < fColorCount; ++i) {
info->fColorOffsets[i] = this->getPos(i);
}
}
}
info->fColorCount = fColorCount;
info->fTileMode = fTileMode;
info->fGradientFlags =
this->interpolateInPremul() ? SkGradientShader::kInterpolateColorsInPremul_Flag : 0;
}
}
// Return true if these parameters are valid/legal/safe to construct a gradient
//
bool SkGradientShaderBase::ValidGradient(const SkColor4f colors[], int count, SkTileMode tileMode,
const Interpolation& interpolation) {
return nullptr != colors && count >= 1 && (unsigned)tileMode < kSkTileModeCount &&
(unsigned)interpolation.fColorSpace < Interpolation::kColorSpaceCount &&
(unsigned)interpolation.fHueMethod < Interpolation::kHueMethodCount;
}
SkGradientShaderBase::Descriptor::Descriptor(const SkColor4f colors[],
sk_sp<SkColorSpace> colorSpace,
const SkScalar positions[],
int colorCount,
SkTileMode mode,
const Interpolation& interpolation)
: fColors(colors)
, fColorSpace(std::move(colorSpace))
, fPositions(positions)
, fColorCount(colorCount)
, fTileMode(mode)
, fInterpolation(interpolation) {
SkASSERT(fColorCount > 1);
}
static SkColor4f average_gradient_color(const SkColor4f colors[], const SkScalar pos[],
int colorCount) {
// The gradient is a piecewise linear interpolation between colors. For a given interval,
// the integral between the two endpoints is 0.5 * (ci + cj) * (pj - pi), which provides that
// intervals average color. The overall average color is thus the sum of each piece. The thing
// to keep in mind is that the provided gradient definition may implicitly use p=0 and p=1.
skvx::float4 blend(0.0f);
for (int i = 0; i < colorCount - 1; ++i) {
// Calculate the average color for the interval between pos(i) and pos(i+1)
auto c0 = skvx::float4::Load(&colors[i]);
auto c1 = skvx::float4::Load(&colors[i + 1]);
// when pos == null, there are colorCount uniformly distributed stops, going from 0 to 1,
// so pos[i + 1] - pos[i] = 1/(colorCount-1)
SkScalar w;
if (pos) {
// Match position fixing in SkGradientShader's constructor, clamping positions outside
// [0, 1] and forcing the sequence to be monotonic
SkScalar p0 = SkTPin(pos[i], 0.f, 1.f);
SkScalar p1 = SkTPin(pos[i + 1], p0, 1.f);
w = p1 - p0;
// And account for any implicit intervals at the start or end of the positions
if (i == 0) {
if (p0 > 0.0f) {
// The first color is fixed between p = 0 to pos[0], so 0.5*(ci + cj)*(pj - pi)
// becomes 0.5*(c + c)*(pj - 0) = c * pj
auto c = skvx::float4::Load(&colors[0]);
blend += p0 * c;
}
}
if (i == colorCount - 2) {
if (p1 < 1.f) {
// The last color is fixed between pos[n-1] to p = 1, so 0.5*(ci + cj)*(pj - pi)
// becomes 0.5*(c + c)*(1 - pi) = c * (1 - pi)
auto c = skvx::float4::Load(&colors[colorCount - 1]);
blend += (1.f - p1) * c;
}
}
} else {
w = 1.f / (colorCount - 1);
}
blend += 0.5f * w * (c1 + c0);
}
SkColor4f avg;
blend.store(&avg);
return avg;
}
// Except for special circumstances of clamped gradients, every gradient shape--when degenerate--
// can be mapped to the same fallbacks. The specific shape factories must account for special
// clamped conditions separately, this will always return the last color for clamped gradients.
sk_sp<SkShader> SkGradientShaderBase::MakeDegenerateGradient(const SkColor4f colors[],
const SkScalar pos[],
int colorCount,
sk_sp<SkColorSpace> colorSpace,
SkTileMode mode) {
switch(mode) {
case SkTileMode::kDecal:
// normally this would reject the area outside of the interpolation region, so since
// inside region is empty when the radii are equal, the entire draw region is empty
return SkShaders::Empty();
case SkTileMode::kRepeat:
case SkTileMode::kMirror:
// repeat and mirror are treated the same: the border colors are never visible,
// but approximate the final color as infinite repetitions of the colors, so
// it can be represented as the average color of the gradient.
return SkShaders::Color(
average_gradient_color(colors, pos, colorCount), std::move(colorSpace));
case SkTileMode::kClamp:
// Depending on how the gradient shape degenerates, there may be a more specialized
// fallback representation for the factories to use, but this is a reasonable default.
return SkShaders::Color(colors[colorCount - 1], std::move(colorSpace));
}
SkDEBUGFAIL("Should not be reached");
return nullptr;
}
SkGradientShaderBase::ColorStopOptimizer::ColorStopOptimizer(const SkColor4f* colors,
const SkScalar* pos,
int count,
SkTileMode mode)
: fColors(colors)
, fPos(pos)
, fCount(count) {
if (!pos || count != 3) {
return;
}
if (SkScalarNearlyEqual(pos[0], 0.0f) &&
SkScalarNearlyEqual(pos[1], 0.0f) &&
SkScalarNearlyEqual(pos[2], 1.0f)) {
if (SkTileMode::kRepeat == mode || SkTileMode::kMirror == mode ||
colors[0] == colors[1]) {
// Ignore the leftmost color/pos.
fColors += 1;
fPos += 1;
fCount = 2;
}
} else if (SkScalarNearlyEqual(pos[0], 0.0f) &&
SkScalarNearlyEqual(pos[1], 1.0f) &&
SkScalarNearlyEqual(pos[2], 1.0f)) {
if (SkTileMode::kRepeat == mode || SkTileMode::kMirror == mode ||
colors[1] == colors[2]) {
// Ignore the rightmost color/pos.
fCount = 2;
}
}
}