2 * Copyright 2016 Google Inc.
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
8 #include "include/core/SkPaint.h"
9 #include "include/private/SkTPin.h"
10 #include "src/shaders/gradients/Sk4fLinearGradient.h"
17 template<ApplyPremul premul>
18 void ramp(const skvx::float4& c, const skvx::float4& dc, SkPMColor dst[], int n,
19 const skvx::float4& bias0, const skvx::float4& bias1) {
22 const auto dc2 = dc + dc,
25 auto c0 = c + DstTraits<premul>::pre_lerp_bias(bias0),
26 c1 = c + dc + DstTraits<premul>::pre_lerp_bias(bias1),
31 DstTraits<premul>::store4x(c0, c1, c2, c3, dst, bias0, bias1);
41 DstTraits<premul>::store(c0, dst++, bias0);
42 DstTraits<premul>::store(c1, dst++, bias1);
46 DstTraits<premul>::store(c0, dst, bias0);
51 SkScalar pinFx(SkScalar);
54 SkScalar pinFx<SkTileMode::kClamp>(SkScalar fx) {
59 SkScalar pinFx<SkTileMode::kRepeat>(SkScalar fx) {
60 SkScalar f = SkScalarIsFinite(fx) ? SkScalarFraction(fx) : 0;
62 f = std::min(f + 1, nextafterf(1, 0));
70 SkScalar pinFx<SkTileMode::kMirror>(SkScalar fx) {
71 SkScalar f = SkScalarIsFinite(fx) ? SkScalarMod(fx, 2.0f) : 0;
73 f = std::min(f + 2, nextafterf(2, 0));
80 // true when x is in [k1,k2], or [k2, k1] when the interval is reversed.
81 // TODO(fmalita): hoist the reversed interval check out of this helper.
82 bool in_range(SkScalar x, SkScalar k1, SkScalar k2) {
85 ? (x >= k1 && x <= k2)
86 : (x >= k2 && x <= k1);
89 } // anonymous namespace
92 LinearGradient4fContext::LinearGradient4fContext(const SkLinearGradient& shader,
93 const ContextRec& rec)
94 : INHERITED(shader, rec) {
96 // Our fast path expects interval points to be monotonically increasing in x.
97 const bool reverseIntervals = std::signbit(fDstToPos.getScaleX());
98 fIntervals.init(shader, rec.fDstColorSpace, shader.fTileMode,
99 fColorsArePremul, rec.fPaintAlpha * (1.0f / 255), reverseIntervals);
101 SkASSERT(fIntervals->count() > 0);
102 fCachedInterval = fIntervals->begin();
105 const Sk4fGradientInterval*
106 SkLinearGradient::LinearGradient4fContext::findInterval(SkScalar fx) const {
107 SkASSERT(in_range(fx, fIntervals->front().fT0, fIntervals->back().fT1));
110 // Linear search, using the last scanline interval as a starting point.
111 SkASSERT(fCachedInterval >= fIntervals->begin());
112 SkASSERT(fCachedInterval < fIntervals->end());
113 const int search_dir = fDstToPos.getScaleX() >= 0 ? 1 : -1;
114 while (!in_range(fx, fCachedInterval->fT0, fCachedInterval->fT1)) {
115 fCachedInterval += search_dir;
116 if (fCachedInterval >= fIntervals->end()) {
117 fCachedInterval = fIntervals->begin();
118 } else if (fCachedInterval < fIntervals->begin()) {
119 fCachedInterval = fIntervals->end() - 1;
122 return fCachedInterval;
124 // Binary search. Seems less effective than linear + caching.
125 const auto* i0 = fIntervals->begin();
126 const auto* i1 = fIntervals->end() - 1;
130 SkASSERT(in_range(fx, i0->fT0, i1->fT1));
132 const auto* i = i0 + ((i1 - i0) >> 1);
134 if (in_range(fx, i0->fT0, i->fT1)) {
137 SkASSERT(in_range(fx, i->fT1, i1->fT1));
142 SkASSERT(in_range(fx, i0->fT0, i0->fT1));
148 void SkLinearGradient::
149 LinearGradient4fContext::shadeSpan(int x, int y, SkPMColor dst[], int count) {
156 static constexpr float dither_cell[] = {
161 const int rowIndex = (y & 1) << 1;
162 bias0 = dither_cell[rowIndex + 0];
163 bias1 = dither_cell[rowIndex + 1];
171 if (fColorsArePremul) {
172 // In premul interpolation mode, components are pre-scaled by 255 and the store
173 // op is truncating. We pre-bias here to achieve rounding.
177 this->shadePremulSpan<ApplyPremul::False>(x, y, dst, count, bias0, bias1);
179 // In unpremul interpolation mode, Components are not pre-scaled.
183 this->shadePremulSpan<ApplyPremul::True >(x, y, dst, count, bias0, bias1);
187 template<ApplyPremul premul>
188 void SkLinearGradient::
189 LinearGradient4fContext::shadePremulSpan(int x, int y, SkPMColor dst[], int count,
190 float bias0, float bias1) const {
191 const SkLinearGradient& shader = static_cast<const SkLinearGradient&>(fShader);
192 switch (shader.fTileMode) {
193 case SkTileMode::kDecal:
194 SkASSERT(false); // decal only supported via stages
196 case SkTileMode::kClamp:
197 this->shadeSpanInternal<premul, SkTileMode::kClamp >(x, y, dst, count, bias0, bias1);
199 case SkTileMode::kRepeat:
200 this->shadeSpanInternal<premul, SkTileMode::kRepeat>(x, y, dst, count, bias0, bias1);
202 case SkTileMode::kMirror:
203 this->shadeSpanInternal<premul, SkTileMode::kMirror>(x, y, dst, count, bias0, bias1);
208 template<ApplyPremul premul, SkTileMode tileMode>
209 void SkLinearGradient::
210 LinearGradient4fContext::shadeSpanInternal(int x, int y, SkPMColor dst[], int count,
211 float bias0, float bias1) const {
213 fDstToPosProc(fDstToPos,
217 const SkScalar fx = pinFx<tileMode>(pt.x());
218 const SkScalar dx = fDstToPos.getScaleX();
219 LinearIntervalProcessor<premul, tileMode> proc(fIntervals->begin(),
220 fIntervals->end() - 1,
221 this->findInterval(fx),
224 SkScalarNearlyZero(dx * count));
225 skvx::float4 bias4f0(bias0),
229 // What we really want here is SkTPin(advance, 1, count)
230 // but that's a significant perf hit for >> stops; investigate.
231 const int n = std::min(SkScalarTruncToInt(proc.currentAdvance() + 1), count);
233 // The current interval advance can be +inf (e.g. when reaching
234 // the clamp mode end intervals) - when that happens, we expect to
235 // a) consume all remaining count in one swoop
236 // b) return a zero color gradient
237 SkASSERT(SkScalarIsFinite(proc.currentAdvance())
238 || (n == count && proc.currentRampIsZero()));
240 if (proc.currentRampIsZero()) {
241 DstTraits<premul>::store(proc.currentColor(), dst, n);
243 ramp<premul>(proc.currentColor(), proc.currentColorGrad(), dst, n,
247 proc.advance(SkIntToScalar(n));
253 swap(bias4f0, bias4f1);
258 template<ApplyPremul premul, SkTileMode tileMode>
259 class SkLinearGradient::
260 LinearGradient4fContext::LinearIntervalProcessor {
262 LinearIntervalProcessor(const Sk4fGradientInterval* firstInterval,
263 const Sk4fGradientInterval* lastInterval,
264 const Sk4fGradientInterval* i,
268 : fAdvX(is_vertical ? SK_ScalarInfinity : (i->fT1 - fx) / dx)
269 , fFirstInterval(firstInterval)
270 , fLastInterval(lastInterval)
273 , fIsVertical(is_vertical)
275 SkASSERT(fAdvX >= 0);
276 SkASSERT(firstInterval <= lastInterval);
278 if (tileMode != SkTileMode::kClamp && !is_vertical) {
279 const auto spanX = (lastInterval->fT1 - firstInterval->fT0) / dx;
280 SkASSERT(spanX >= 0);
282 // If we're in a repeating tile mode and the whole gradient is compressed into a
283 // fraction of a pixel, we just use the average color in zero-ramp mode.
284 // This also avoids cases where we make no progress due to interval advances being
286 static constexpr SkScalar kMinSpanX = .25f;
287 if (spanX < kMinSpanX) {
288 this->init_average_props();
293 this->compute_interval_props(fx);
296 SkScalar currentAdvance() const {
297 SkASSERT(fAdvX >= 0);
298 SkASSERT(!std::isfinite(fAdvX) || fAdvX <= (fInterval->fT1 - fInterval->fT0) / fDx);
302 bool currentRampIsZero() const { return fZeroRamp; }
303 const skvx::float4& currentColor() const { return fCc; }
304 const skvx::float4& currentColorGrad() const { return fDcDx; }
306 void advance(SkScalar advX) {
308 SkASSERT(fAdvX >= 0);
311 advX = this->advance_interval(advX);
313 SkASSERT(advX < fAdvX);
315 fCc = fCc + fDcDx * advX;
320 void compute_interval_props(SkScalar t) {
321 SkASSERT(in_range(t, fInterval->fT0, fInterval->fT1));
323 const auto dc = DstTraits<premul>::load(fInterval->fCg);
324 fCc = DstTraits<premul>::load(fInterval->fCb) + dc * t;
326 fZeroRamp = fIsVertical || all(dc == 0);
329 void init_average_props() {
330 fAdvX = SK_ScalarInfinity;
335 // TODO: precompute the average at interval setup time?
336 for (const auto* i = fFirstInterval; i <= fLastInterval; ++i) {
337 // Each interval contributes its average color to the total/weighted average:
339 // C = (c0 + c1) / 2 = (Cb + Cg * t0 + Cb + Cg * t1) / 2 = Cb + Cg *(t0 + t1) / 2
341 // Avg += C * (t1 - t0)
343 const auto c = DstTraits<premul>::load(i->fCb)
344 + DstTraits<premul>::load(i->fCg) * (i->fT0 + i->fT1) * 0.5f;
345 fCc = fCc + c * (i->fT1 - i->fT0);
349 const Sk4fGradientInterval* next_interval(const Sk4fGradientInterval* i) const {
350 SkASSERT(i >= fFirstInterval);
351 SkASSERT(i <= fLastInterval);
354 if (tileMode == SkTileMode::kClamp) {
355 SkASSERT(i <= fLastInterval);
359 return (i <= fLastInterval) ? i : fFirstInterval;
362 SkScalar advance_interval(SkScalar advX) {
363 SkASSERT(advX >= fAdvX);
367 fInterval = this->next_interval(fInterval);
368 fAdvX = (fInterval->fT1 - fInterval->fT0) / fDx;
369 SkASSERT(fAdvX >= 0); // fT1 must be bigger than fT0 but fAdvX can underflow.
370 } while (advX >= fAdvX);
372 compute_interval_props(fInterval->fT0);
378 // Current interval properties.
379 skvx::float4 fDcDx; // dst color gradient (dc/dx)
380 skvx::float4 fCc; // current color, interpolated in dst
381 SkScalar fAdvX; // remaining interval advance in dst
382 bool fZeroRamp; // current interval color grad is 0
384 const Sk4fGradientInterval* fFirstInterval;
385 const Sk4fGradientInterval* fLastInterval;
386 const Sk4fGradientInterval* fInterval; // current interval
387 const SkScalar fDx; // 'dx' for consistency with other impls; actually dt/dx
388 const bool fIsVertical;