Relocate the specialized linear gradient interval builder

src/effects/gradients/Sk4fGradientBase.cpp

Index: src/effects/gradients/Sk4fGradientBase.cpp
diff --git a/src/effects/gradients/Sk4fGradientBase.cpp b/src/effects/gradients/Sk4fGradientBase.cpp
index b3bc24658b7c5a6ed5bcab6c2e2f71694dbefe19..bd3c51a0352cccdbce31a7afb514419b13a13644 100644
--- a/src/effects/gradients/Sk4fGradientBase.cpp
+++ b/src/effects/gradients/Sk4fGradientBase.cpp
@@ -9,14 +9,6 @@
 
 namespace {
 
-const float kInv255Float = 1.0f / 255;
-
-SkPMColor pack_color(SkColor c, bool premul) {
-    return premul
-        ? SkPreMultiplyColor(c)
-        : SkPackARGB32NoCheck(SkColorGetA(c), SkColorGetR(c), SkColorGetG(c), SkColorGetB(c));
-}
-
 // true when x is in [k1,k2)
 bool in_range(SkScalar x, SkScalar k1, SkScalar k2) {
     SkASSERT(k1 != k2);
@@ -25,83 +17,6 @@ bool in_range(SkScalar x, SkScalar k1, SkScalar k2) {
         : (x >= k2 && x < k1);
 }
 
-class IntervalBuilder {
-public:
-    IntervalBuilder(const SkColor* colors, const SkScalar* pos, int count, bool reverse)
-        : fColors(colors)
-        , fPos(pos)
-        , fCount(count)
-        , fFirstPos(reverse ? SK_Scalar1 : 0)
-        , fBegin(reverse ? count - 1 : 0)
-        , fAdvance(reverse ? -1 : 1) {
-        SkASSERT(colors);
-        SkASSERT(count > 1);
-    }
-
-    template<typename F>
-    void build(F func) const {
-        if (!fPos) {
-            this->buildImplicitPos(func);
-            return;
-        }
-
-        const int end = fBegin + fAdvance * (fCount - 1);
-        const SkScalar lastPos = 1 - fFirstPos;
-        int prev = fBegin;
-        SkScalar prevPos = fFirstPos;
-
-        do {
-            const int curr = prev + fAdvance;
-            SkASSERT(curr >= 0 && curr < fCount);
-
-            // TODO: this sanitization should be done in SkGradientShaderBase
-            const SkScalar currPos = (fAdvance > 0)
-                ? SkTPin(fPos[curr], prevPos, lastPos)
-                : SkTPin(fPos[curr], lastPos, prevPos);
-
-            if (currPos != prevPos) {
-                SkASSERT((currPos - prevPos > 0) == (fAdvance > 0));
-                func(fColors[prev], fColors[curr], prevPos, currPos);
-            }
-
-            prev = curr;
-            prevPos = currPos;
-        } while (prev != end);
-    }
-
-private:
-    template<typename F>
-    void buildImplicitPos(F func) const {
-        // When clients don't provide explicit color stop positions (fPos == nullptr),
-        // the color stops are distributed evenly across the unit interval
-        // (implicit positioning).
-        const SkScalar dt = fAdvance * SK_Scalar1 / (fCount - 1);
-        const int end = fBegin + fAdvance * (fCount - 2);
-        int prev = fBegin;
-        SkScalar prevPos = fFirstPos;
-
-        while (prev != end) {
-            const int curr = prev + fAdvance;
-            SkASSERT(curr >= 0 && curr < fCount);
-
-            const SkScalar currPos = prevPos + dt;
-            func(fColors[prev], fColors[curr], prevPos, currPos);
-            prev = curr;
-            prevPos = currPos;
-        }
-
-        // emit the last interval with a pinned end position, to avoid precision issues
-        func(fColors[prev], fColors[prev + fAdvance], prevPos, 1 - fFirstPos);
-    }
-
-    const SkColor*  fColors;
-    const SkScalar* fPos;
-    const int       fCount;
-    const SkScalar  fFirstPos;
-    const int       fBegin;
-    const int       fAdvance;
-};
-
 } // anonymous namespace
 
 SkGradientShaderBase::GradientShaderBase4fContext::
@@ -147,49 +62,6 @@ GradientShaderBase4fContext::GradientShaderBase4fContext(const SkGradientShaderB
     , fDither(rec.fPaint->isDither())
 #endif
 {
-    // The main job here is to build an interval list.  Intervals are a different
-    // representation of the color stops data, optimized for efficient scan line
-    // access during shading.
-    //
-    //   [{P0,C0} , {P1,C1}) [{P1,C2} , {P2,c3}) ... [{Pn,C2n} , {Pn+1,C2n+1})
-    //
-    // The list is sorted in increasing dst order, i.e. X(Pk) < X(Pk+1).  This
-    // allows us to always traverse left->right when iterating over a scan line.
-    // It also means that the interval order matches the color stops when dx >= 0,
-    // and is the inverse (pos, colors, order are flipped) when dx < 0.
-    //
-    // Note: the current representation duplicates pos data; we could refactor to
-    //       avoid this if interval storage size becomes a concern.
-    //
-    // Aside from reordering, we also perform two more pre-processing steps at
-    // this stage:
-    //
-    //   1) scale the color components depending on paint alpha and the requested
-    //      interpolation space (note: the interval color storage is SkPM4f, but
-    //      that doesn't necessarily mean the colors are premultiplied; that
-    //      property is tracked in fColorsArePremul)
-    //
-    //   2) inject synthetic intervals to support tiling.
-    //
-    //      * for kRepeat, no extra intervals are needed - the iterator just
-    //        wraps around at the end:
-    //
-    //          ->[P0,P1)->..[Pn-1,Pn)->
-    //
-    //      * for kClamp, we add two "infinite" intervals before/after:
-    //
-    //          [-/+inf , P0)->[P0 , P1)->..[Pn-1 , Pn)->[Pn , +/-inf)
-    //
-    //        (the iterator should never run off the end in this mode)
-    //
-    //      * for kMirror, we extend the range to [0..2] and add a flipped
-    //        interval series - then the iterator operates just as in the
-    //        kRepeat case:
-    //
-    //          ->[P0,P1)->..[Pn-1,Pn)->[2 - Pn,2 - Pn-1)->..[2 - P1,2 - P0)->
-    //
-    // TODO: investigate collapsing intervals << 1px.
-
     const SkMatrix& inverse = this->getTotalInverse();
     fDstToPos.setConcat(shader.fPtsToUnit, inverse);
     fDstToPosProc = fDstToPos.getMapXYProc();
@@ -202,123 +74,4 @@ GradientShaderBase4fContext::GradientShaderBase4fContext(const SkGradientShaderB
     fColorsArePremul =
         (shader.fGradFlags & SkGradientShader::kInterpolateColorsInPremul_Flag)
         || shader.fColorsAreOpaque;
-
-    const float paintAlpha = rec.fPaint->getAlpha() * kInv255Float;
-    const Sk4f componentScale = fColorsArePremul
-        ? Sk4f(paintAlpha * kInv255Float)
-        : Sk4f(kInv255Float, kInv255Float, kInv255Float, paintAlpha * kInv255Float);
-
-    SkASSERT(shader.fColorCount > 1);
-    SkASSERT(shader.fOrigColors);
-
-    const bool dx_is_pos = fDstToPos.getScaleX() >= 0;
-    const int first_index = dx_is_pos ? 0 : shader.fColorCount - 1;
-    const int last_index = shader.fColorCount - 1 - first_index;
-    const SkScalar first_pos = dx_is_pos ? 0 : SK_Scalar1;
-    const SkScalar last_pos = 1 - first_pos;
-
-    if (shader.fTileMode == SkShader::kClamp_TileMode) {
-        // synthetic edge interval: -/+inf .. P0
-        const SkPMColor clamp_color = pack_color(shader.fOrigColors[first_index],
-                                                 fColorsArePremul);
-        const SkScalar clamp_pos = dx_is_pos ? SK_ScalarMin : SK_ScalarMax;
-        fIntervals.emplace_back(clamp_color, clamp_pos,
-                                clamp_color, first_pos,
-                                componentScale);
-    } else if (shader.fTileMode == SkShader::kMirror_TileMode && !dx_is_pos) {
-        // synthetic mirror intervals injected before main intervals: (2 .. 1]
-        addMirrorIntervals(shader, componentScale, dx_is_pos);
-    }
-
-    const IntervalBuilder builder(shader.fOrigColors,
-                                  shader.fOrigPos,
-                                  shader.fColorCount,
-                                  !dx_is_pos);
-    builder.build([this, &componentScale] (SkColor c0, SkColor c1, SkScalar p0, SkScalar p1) {
-        SkASSERT(fIntervals.empty() || fIntervals.back().fP1 == p0);
-
-        fIntervals.emplace_back(pack_color(c0, fColorsArePremul),
-                                p0,
-                                pack_color(c1, fColorsArePremul),
-                                p1,
-                                componentScale);
-    });
-
-    if (shader.fTileMode == SkShader::kClamp_TileMode) {
-        // synthetic edge interval: Pn .. +/-inf
-        const SkPMColor clamp_color =
-            pack_color(shader.fOrigColors[last_index], fColorsArePremul);
-        const SkScalar clamp_pos = dx_is_pos ? SK_ScalarMax : SK_ScalarMin;
-        fIntervals.emplace_back(clamp_color, last_pos,
-                                clamp_color, clamp_pos,
-                                componentScale);
-    } else if (shader.fTileMode == SkShader::kMirror_TileMode && dx_is_pos) {
-        // synthetic mirror intervals injected after main intervals: [1 .. 2)
-        addMirrorIntervals(shader, componentScale, dx_is_pos);
-    }
-
-    SkASSERT(fIntervals.count() > 0);
-    fCachedInterval = fIntervals.begin();
-}
-
-void SkGradientShaderBase::
-GradientShaderBase4fContext::addMirrorIntervals(const SkGradientShaderBase& shader,
-                                                const Sk4f& componentScale, bool dx_is_pos) {
-    // Iterates in reverse order (vs main interval builder) and adds intervals reflected in 2.
-    const IntervalBuilder builder(shader.fOrigColors,
-                                  shader.fOrigPos,
-                                  shader.fColorCount,
-                                  dx_is_pos);
-    builder.build([this, &componentScale] (SkColor c0, SkColor c1, SkScalar p0, SkScalar p1) {
-        SkASSERT(fIntervals.empty() || fIntervals.back().fP1 == 2 - p0);
-
-        fIntervals.emplace_back(pack_color(c0, fColorsArePremul),
-                                2 - p0,
-                                pack_color(c1, fColorsArePremul),
-                                2 - p1,
-                                componentScale);
-    });
-}
-
-const SkGradientShaderBase::GradientShaderBase4fContext::Interval*
-SkGradientShaderBase::
-GradientShaderBase4fContext::findInterval(SkScalar fx) const {
-    SkASSERT(in_range(fx, fIntervals.front().fP0, fIntervals.back().fP1));
-
-    if (1) {
-        // Linear search, using the last scanline interval as a starting point.
-        SkASSERT(fCachedInterval >= fIntervals.begin());
-        SkASSERT(fCachedInterval < fIntervals.end());
-        const int search_dir = fDstToPos.getScaleX() >= 0 ? 1 : -1;
-        while (!in_range(fx, fCachedInterval->fP0, fCachedInterval->fP1)) {
-            fCachedInterval += search_dir;
-            if (fCachedInterval >= fIntervals.end()) {
-                fCachedInterval = fIntervals.begin();
-            } else if (fCachedInterval < fIntervals.begin()) {
-                fCachedInterval = fIntervals.end() - 1;
-            }
-        }
-        return fCachedInterval;
-    } else {
-        // Binary search.  Seems less effective than linear + caching.
-        const Interval* i0 = fIntervals.begin();
-        const Interval* i1 = fIntervals.end() - 1;
-
-        while (i0 != i1) {
-            SkASSERT(i0 < i1);
-            SkASSERT(in_range(fx, i0->fP0, i1->fP1));
-
-            const Interval* i = i0 + ((i1 - i0) >> 1);
-
-            if (in_range(fx, i0->fP0, i->fP1)) {
-                i1 = i;
-            } else {
-                SkASSERT(in_range(fx, i->fP1, i1->fP1));
-                i0 = i + 1;
-            }
-        }
-
-        SkASSERT(in_range(fx, i0->fP0, i0->fP1));
-        return i0;
-    }
 }