Initial linear gradient 4f impl

src/effects/gradients/Sk4fLinearGradient.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Sk4fLinearGradient.h"
+
+namespace {
+
+Sk4f premul_4f(const Sk4f& c) {
+    const float alpha = c[SkPM4f::A];
+    // FIXME: portable swizzle?
+    return c * Sk4f(alpha, alpha, alpha, 1);
+}
+
+template <bool do_premul>
+SkPMColor trunc_from_255(const Sk4f& c) {
+    SkPMColor pmc;
+    SkNx_cast<uint8_t>(c).store(&pmc);
+    if (do_premul) {
+        pmc = SkPreMultiplyARGB(SkGetPackedA32(pmc), SkGetPackedR32(pmc),
+                                SkGetPackedG32(pmc), SkGetPackedB32(pmc));
+    }
+    return pmc;
+}
+
+template<typename DstType, bool do_premul>
+void fill(const Sk4f& c, DstType* dst, int n);
+
+template<>
+void fill<SkPM4f, false>(const Sk4f& c, SkPM4f* dst, int n) {
+    while (n > 0) {
+        c.store(dst++);
+        n--;
+    }
+}
+
+template<>
+void fill<SkPM4f, true>(const Sk4f& c, SkPM4f* dst, int n) {
+    fill<SkPM4f, false>(premul_4f(c), dst, n);
+}
+
+template<>
+void fill<SkPMColor, false>(const Sk4f& c, SkPMColor* dst, int n) {
+    sk_memset32(dst, trunc_from_255<false>(c), n);
+}
+
+template<>
+void fill<SkPMColor, true>(const Sk4f& c, SkPMColor* dst, int n) {
+    sk_memset32(dst, trunc_from_255<true>(c), n);
+}
+
+template<typename DstType, bool do_premul>
+void store(const Sk4f& color, DstType* dst);
+
+template<>
+void store<SkPM4f, false>(const Sk4f& c, SkPM4f* dst) {
+    c.store(dst);
+}
+
+template<>
+void store<SkPM4f, true>(const Sk4f& c, SkPM4f* dst) {
+    store<SkPM4f, false>(premul_4f(c), dst);
+}
+
+template<>
+void store<SkPMColor, false>(const Sk4f& c, SkPMColor* dst) {
+    *dst = trunc_from_255<false>(c);
+}
+
+template<>
+void store<SkPMColor, true>(const Sk4f& c, SkPMColor* dst) {
+    *dst = trunc_from_255<true>(c);
+}
+
+template<typename DstType, bool do_premul>
+void store4x(const Sk4f& c0,
+             const Sk4f& c1,
+             const Sk4f& c2,
+             const Sk4f& c3,
+             DstType* dst) {
+    store<DstType, do_premul>(c0, dst++);
+    store<DstType, do_premul>(c1, dst++);
+    store<DstType, do_premul>(c2, dst++);
+    store<DstType, do_premul>(c3, dst++);
+}
+
+template<>
+void store4x<SkPMColor, false>(const Sk4f& c0,
+                               const Sk4f& c1,
+                               const Sk4f& c2,
+                               const Sk4f& c3,
+                               SkPMColor* dst) {
+    Sk4f_ToBytes((uint8_t*)dst, c0, c1, c2, c3);
+}
+
+template<typename DstType, bool do_premul>
+void ramp(const Sk4f& c, const Sk4f& dc, DstType* dst, int n) {
+    SkASSERT(n > 0);
+
+    const Sk4f dc2 = dc + dc;
+    const Sk4f dc4 = dc2 + dc2;
+
+    Sk4f c0 = c ;
+    Sk4f c1 = c + dc;
+    Sk4f c2 = c0 + dc2;
+    Sk4f c3 = c1 + dc2;
+
+    while (n >= 4) {
+        store4x<DstType, do_premul>(c0, c1, c2, c3, dst);
+        dst += 4;
+
+        c0 = c0 + dc4;
+        c1 = c1 + dc4;
+        c2 = c2 + dc4;
+        c3 = c3 + dc4;
+        n -= 4;
+    }
+    if (n & 2) {
+        store<DstType, do_premul>(c0, dst++);
+        store<DstType, do_premul>(c1, dst++);
+        c0 = c0 + dc2;
+    }
+    if (n & 1) {
+        store<DstType, do_premul>(c0, dst);
+    }
+}
+
+template<SkShader::TileMode>
+SkScalar pinFx(SkScalar);
+
+template<>
+SkScalar pinFx<SkShader::kClamp_TileMode>(SkScalar fx) {
+    return fx;
+}
+
+template<>
+SkScalar pinFx<SkShader::kRepeat_TileMode>(SkScalar fx) {
+    const SkScalar f = SkScalarFraction(fx);
+    return f < 0 ? f + 1 : f;
+}
+
+template<>
+SkScalar pinFx<SkShader::kMirror_TileMode>(SkScalar fx) {
+    const SkScalar f = SkScalarMod(fx, 2.0f);
+    return f < 0 ? f + 2 : f;
+}
+
+template<typename DstType>
+float dst_component_scale();
+
+template<>
+float dst_component_scale<SkPM4f>() {
+    return 1;
+}
+
+template<>
+float dst_component_scale<SkPMColor>() {
+    return 255;
+}
+
+} // anonymous namespace
+
+SkLinearGradient::
+LinearGradient4fContext::LinearGradient4fContext(const SkLinearGradient& shader,
+                                                 const ContextRec& rec)
+    : INHERITED(shader, rec) {}
+
+void SkLinearGradient::
+LinearGradient4fContext::shadeSpan(int x, int y, SkPMColor dst[], int count) {
+    // TODO: plumb dithering
+    SkASSERT(count > 0);
+    if (fColorsArePremul) {
+        this->shadePremulSpan<SkPMColor, false>(x, y, dst, count);
+    } else {
+        this->shadePremulSpan<SkPMColor, true>(x, y, dst, count);
+    }
+}
+
+void SkLinearGradient::
+LinearGradient4fContext::shadeSpan4f(int x, int y, SkPM4f dst[], int count) {
+    // TONOTDO: plumb dithering
+    SkASSERT(count > 0);
+    if (fColorsArePremul) {
+        this->shadePremulSpan<SkPM4f, false>(x, y, dst, count);
+    } else {
+        this->shadePremulSpan<SkPM4f, true>(x, y, dst, count);
+    }
+}
+
+template<typename DstType, bool do_premul>
+void SkLinearGradient::
+LinearGradient4fContext::shadePremulSpan(int x, int y,
+                                         DstType dst[],
+                                         int count) const {
+    const SkLinearGradient& shader =
+        static_cast<const SkLinearGradient&>(fShader);
+    switch (shader.fTileMode) {
+    case kClamp_TileMode:
+        this->shadeSpanInternal<DstType,
+                                do_premul,
+                                kClamp_TileMode>(x, y, dst, count);
+        break;
+    case kRepeat_TileMode:
+        this->shadeSpanInternal<DstType,
+                                do_premul,
+                                kRepeat_TileMode>(x, y, dst, count);
+        break;
+    case kMirror_TileMode:
+        this->shadeSpanInternal<DstType,
+                                do_premul,
+                                kMirror_TileMode>(x, y, dst, count);
+        break;
+    }
+}
+
+template<typename DstType, bool do_premul, SkShader::TileMode tileMode>
+void SkLinearGradient::
+LinearGradient4fContext::shadeSpanInternal(int x, int y,
+                                           DstType dst[],
+                                           int count) const {
+    SkPoint pt;
+    fDstToPosProc(fDstToPos,
+                  x + SK_ScalarHalf,
+                  y + SK_ScalarHalf,
+                  &pt);
+    const SkScalar fx = pinFx<tileMode>(pt.x());
+    const SkScalar dx = fDstToPos.getScaleX();
+    LinearIntervalProcessor<DstType, tileMode> proc(fIntervals.begin(),
+                                                    fIntervals.end() - 1,
+                                                    this->findInterval(fx),
+                                                    fx,
+                                                    dx,
+                                                    SkScalarNearlyZero(dx * count));
+    while (count > 0) {
+        // What we really want here is SkTPin(advance, 1, count)
+        // but that's a significant perf hit for >> stops; investigate.
+        const int n = SkScalarTruncToInt(
+            SkTMin<SkScalar>(proc.currentAdvance() + 1, SkIntToScalar(count)));
+
+        // The current interval advance can be +inf (e.g. when reaching
+        // the clamp mode end intervals) - when that happens, we expect to
+        //   a) consume all remaining count in one swoop
+        //   b) return a zero color gradient
+        SkASSERT(SkScalarIsFinite(proc.currentAdvance())
+            || (n == count && proc.currentRampIsZero()));
+
+        if (proc.currentRampIsZero()) {
+            fill<DstType, do_premul>(proc.currentColor(),
+                                     dst, n);
+        } else {
+            ramp<DstType, do_premul>(proc.currentColor(),
+                                     proc.currentColorGrad(),
+                                     dst, n);
+        }
+
+        proc.advance(SkIntToScalar(n));
+        count -= n;
+        dst   += n;
+    }
+}
+
+template<typename DstType, SkShader::TileMode tileMode>
+class SkLinearGradient::
+LinearGradient4fContext::LinearIntervalProcessor {
+public:
+    LinearIntervalProcessor(const Interval* firstInterval,
+                            const Interval* lastInterval,
+                            const Interval* i,
+                            SkScalar fx,
+                            SkScalar dx,
+                            bool is_vertical)
+        : fDstComponentScale(dst_component_scale<DstType>())
+        , fAdvX((i->fP1 - fx) / dx)
+        , fFirstInterval(firstInterval)
+        , fLastInterval(lastInterval)
+        , fInterval(i)
+        , fDx(dx)
+        , fIsVertical(is_vertical)
+    {
+        SkASSERT(firstInterval <= lastInterval);
+        SkASSERT(i->contains(fx));
+        this->compute_interval_props(fx - i->fP0);
+    }
+
+    SkScalar currentAdvance() const {
+        SkASSERT(fAdvX >= 0);
+        SkASSERT(fAdvX <= (fInterval->fP1 - fInterval->fP0) / fDx);
+        return fAdvX;
+    }
+
+    bool currentRampIsZero() const { return fZeroRamp; }
+    const Sk4f& currentColor() const { return fCc; }
+    const Sk4f& currentColorGrad() const { return fDcDx; }
+
+    void advance(SkScalar advX) {
+        SkASSERT(advX > 0);
+        SkASSERT(fAdvX >= 0);
+
+        if (advX >= fAdvX) {
+            advX = this->advance_interval(advX);
+        }
+        SkASSERT(advX < fAdvX);
+
+        fCc = fCc + fDcDx * Sk4f(advX);
+        fAdvX -= advX;
+    }
+
+private:
+    void compute_interval_props(SkScalar t) {
+        fDc   = Sk4f::Load(fInterval->fDc.fVec);
+        fCc   = Sk4f::Load(fInterval->fC0.fVec);
+        fCc   = fCc + fDc * Sk4f(t);
+        fCc   = fCc * fDstComponentScale;
+        fDcDx = fDc * fDstComponentScale * Sk4f(fDx);
+        fZeroRamp = fIsVertical || fInterval->isZeroRamp();
+    }
+
+    const Interval* next_interval(const Interval* i) const {
+        SkASSERT(i >= fFirstInterval);
+        SkASSERT(i <= fLastInterval);
+        i++;
+
+        if (tileMode == kClamp_TileMode) {
+            SkASSERT(i <= fLastInterval);
+            return i;
+        }
+
+        return (i <= fLastInterval) ? i : fFirstInterval;
+    }
+
+    SkScalar advance_interval(SkScalar advX) {
+        SkASSERT(advX >= fAdvX);
+
+        do {
+            advX -= fAdvX;
+            fInterval = this->next_interval(fInterval);
+            fAdvX = (fInterval->fP1 - fInterval->fP0) / fDx;
+            SkASSERT(fAdvX > 0);
+        } while (advX >= fAdvX);
+
+        compute_interval_props(0);
+
+        SkASSERT(advX >= 0);
+        return advX;
+    }
+
+    const Sk4f      fDstComponentScale; // cached dst scale (PMC: 255, PM4f: 1)
+
+    // Current interval properties.
+    Sk4f            fDc;        // local color gradient (dc/dt)
+    Sk4f            fDcDx;      // dst color gradient (dc/dx)
+    Sk4f            fCc;        // current color, interpolated in dst
+    SkScalar        fAdvX;      // remaining interval advance in dst
+    bool            fZeroRamp;  // current interval color grad is 0
+
+    const Interval* fFirstInterval;
+    const Interval* fLastInterval;
+    const Interval* fInterval;  // current interval
+    const SkScalar  fDx;        // 'dx' for consistency with other impls; actually dt/dx
+    const bool      fIsVertical;
+};