From: George Wright <gw@gwright.org.uk>
Date: Thu, 25 Apr 2013 20:47:06 -0400
Subject: Bug 848491 - Re-apply bug 687188 - Expand the gradient cache by 2 to store 0/1 colour stop values for clamping.


diff --git a/gfx/skia/src/effects/gradients/SkGradientShader.cpp b/gfx/skia/src/effects/gradients/SkGradientShader.cpp
index 684355d..27a9c46 100644
--- a/gfx/skia/src/effects/gradients/SkGradientShader.cpp
+++ b/gfx/skia/src/effects/gradients/SkGradientShader.cpp
@@ -453,15 +453,15 @@ const uint16_t* SkGradientShaderBase::getCache16() const {
 
 const SkPMColor* SkGradientShaderBase::getCache32() const {
     if (fCache32 == NULL) {
-        // double the count for dither entries
-        const int entryCount = kCache32Count * 4;
+        // double the count for dither entries, and have an extra two entries for clamp values
+        const int entryCount = kCache32Count * 4 + 2;
         const size_t allocSize = sizeof(SkPMColor) * entryCount;
 
         if (NULL == fCache32PixelRef) {
             fCache32PixelRef = SkNEW_ARGS(SkMallocPixelRef,
                                           (NULL, allocSize, NULL));
         }
-        fCache32 = (SkPMColor*)fCache32PixelRef->getAddr();
+        fCache32 = (SkPMColor*)fCache32PixelRef->getAddr() + 1;
         if (fColorCount == 2) {
             Build32bitCache(fCache32, fOrigColors[0], fOrigColors[1],
                             kCache32Count, fCacheAlpha);
@@ -484,7 +484,7 @@ const SkPMColor* SkGradientShaderBase::getCache32() const {
             SkMallocPixelRef* newPR = SkNEW_ARGS(SkMallocPixelRef,
                                                  (NULL, allocSize, NULL));
             SkPMColor* linear = fCache32;           // just computed linear data
-            SkPMColor* mapped = (SkPMColor*)newPR->getAddr();    // storage for mapped data
+            SkPMColor* mapped = (SkPMColor*)newPR->getAddr() + 1;    // storage for mapped data
             SkUnitMapper* map = fMapper;
             for (int i = 0; i < kCache32Count; i++) {
                 int index = map->mapUnit16((i << 8) | i) >> 8;
@@ -495,9 +495,21 @@ const SkPMColor* SkGradientShaderBase::getCache32() const {
             }
             fCache32PixelRef->unref();
             fCache32PixelRef = newPR;
-            fCache32 = (SkPMColor*)newPR->getAddr();
+            fCache32 = (SkPMColor*)newPR->getAddr() + 1;
         }
     }
+
+    // Write the clamp colours into the first and last entries of fCache32
+    fCache32[kCache32ClampLower] = SkPackARGB32(fCacheAlpha,
+                                                SkColorGetR(fOrigColors[0]),
+                                                SkColorGetG(fOrigColors[0]),
+                                                SkColorGetB(fOrigColors[0]));
+
+    fCache32[kCache32ClampUpper] = SkPackARGB32(fCacheAlpha,
+                                                SkColorGetR(fOrigColors[fColorCount - 1]),
+                                                SkColorGetG(fOrigColors[fColorCount - 1]),
+                                                SkColorGetB(fOrigColors[fColorCount - 1]));
+
     return fCache32;
 }
 
diff --git a/gfx/skia/src/effects/gradients/SkGradientShaderPriv.h b/gfx/skia/src/effects/gradients/SkGradientShaderPriv.h
index 729ce4e..2cb6a9d 100644
--- a/gfx/skia/src/effects/gradients/SkGradientShaderPriv.h
+++ b/gfx/skia/src/effects/gradients/SkGradientShaderPriv.h
@@ -86,6 +86,9 @@ public:
         /// if dithering is disabled.
         kDitherStride32 = kCache32Count,
         kDitherStride16 = kCache16Count,
+
+        kCache32ClampLower = -1,
+        kCache32ClampUpper = kCache32Count * 4
     };
 
 
diff --git a/gfx/skia/src/effects/gradients/SkLinearGradient.cpp b/gfx/skia/src/effects/gradients/SkLinearGradient.cpp
index e0f216c..40ab918 100644
--- a/gfx/skia/src/effects/gradients/SkLinearGradient.cpp
+++ b/gfx/skia/src/effects/gradients/SkLinearGradient.cpp
@@ -127,6 +127,17 @@ void shadeSpan_linear_vertical_lerp(TileProc proc, SkFixed dx, SkFixed fx,
                                     SkPMColor* SK_RESTRICT dstC,
                                     const SkPMColor* SK_RESTRICT cache,
                                     int toggle, int count) {
+    if (proc == clamp_tileproc) {
+        // No need to lerp or dither for clamp values
+        if (fx < 0) {
+            sk_memset32(dstC, cache[SkGradientShaderBase::kCache32ClampLower], count);
+            return;
+        } else if (fx > 0xffff) {
+            sk_memset32(dstC, cache[SkGradientShaderBase::kCache32ClampUpper], count);
+            return;
+        }
+    }
+
     // We're a vertical gradient, so no change in a span.
     // If colors change sharply across the gradient, dithering is
     // insufficient (it subsamples the color space) and we need to lerp.
@@ -154,10 +165,7 @@ void shadeSpan_linear_clamp(TileProc proc, SkFixed dx, SkFixed fx,
     range.init(fx, dx, count, 0, SkGradientShaderBase::kCache32Count - 1);
 
     if ((count = range.fCount0) > 0) {
-        sk_memset32_dither(dstC,
-            cache[toggle + range.fV0],
-            cache[next_dither_toggle(toggle) + range.fV0],
-            count);
+        sk_memset32(dstC, cache[SkGradientShaderBase::kCache32ClampLower], count);
         dstC += count;
     }
     if ((count = range.fCount1) > 0) {
@@ -176,10 +184,7 @@ void shadeSpan_linear_clamp(TileProc proc, SkFixed dx, SkFixed fx,
         }
     }
     if ((count = range.fCount2) > 0) {
-        sk_memset32_dither(dstC,
-            cache[toggle + range.fV1],
-            cache[next_dither_toggle(toggle) + range.fV1],
-            count);
+        sk_memset32(dstC, cache[SkGradientShaderBase::kCache32ClampUpper], count);
     }
 }
 
diff --git a/gfx/skia/src/effects/gradients/SkTwoPointConicalGradient.cpp b/gfx/skia/src/effects/gradients/SkTwoPointConicalGradient.cpp
index abd974b..601fff4 100644
--- a/gfx/skia/src/effects/gradients/SkTwoPointConicalGradient.cpp
+++ b/gfx/skia/src/effects/gradients/SkTwoPointConicalGradient.cpp
@@ -124,10 +124,14 @@ static void twopoint_clamp(TwoPtRadial* rec, SkPMColor* SK_RESTRICT dstC,
         if (TwoPtRadial::DontDrawT(t)) {
             *dstC++ = 0;
         } else {
-            SkFixed index = SkClampMax(t, 0xFFFF);
-            SkASSERT(index <= 0xFFFF);
-            *dstC++ = cache[toggle +
-                            (index >> SkGradientShaderBase::kCache32Shift)];
+            if (t < 0) {
+                *dstC++ = cache[SkGradientShaderBase::kCache32ClampLower];
+            } else if (t > 0xFFFF) {
+                *dstC++ = cache[SkGradientShaderBase::kCache32ClampUpper];
+            } else {
+                SkASSERT(t <= 0xFFFF);
+                *dstC++ = cache[t >> SkGradientShaderBase::kCache32Shift];
+            }
         }
         toggle = next_dither_toggle(toggle);
     }
diff --git a/gfx/skia/src/effects/gradients/SkTwoPointRadialGradient.cpp b/gfx/skia/src/effects/gradients/SkTwoPointRadialGradient.cpp
index f70b67d..ec2ae75 100644
--- a/gfx/skia/src/effects/gradients/SkTwoPointRadialGradient.cpp
+++ b/gfx/skia/src/effects/gradients/SkTwoPointRadialGradient.cpp
@@ -120,9 +120,14 @@ void shadeSpan_twopoint_clamp(SkScalar fx, SkScalar dx,
     for (; count > 0; --count) {
         SkFixed t = two_point_radial(b, fx, fy, fSr2D2, foura,
                                      fOneOverTwoA, posRoot);
-        SkFixed index = SkClampMax(t, 0xFFFF);
-        SkASSERT(index <= 0xFFFF);
-        *dstC++ = cache[index >> SkGradientShaderBase::kCache32Shift];
+        if (t < 0) {
+            *dstC++ = cache[SkGradientShaderBase::kCache32ClampLower];
+        } else if (t > 0xFFFF) {
+            *dstC++ = cache[SkGradientShaderBase::kCache32ClampUpper];
+        } else {
+            SkASSERT(t <= 0xFFFF);
+            *dstC++ = cache[t >> SkGradientShaderBase::kCache32Shift];
+        }
         fx += dx;
         fy += dy;
         b += db;
-- 
1.7.11.7