Extract most of the mutable state of SkShader into a separate Context object.

src/effects/gradients/SkGradientShader.cpp

Index: src/effects/gradients/SkGradientShader.cpp
diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 5b0b9c763da184ec9b732112cbb2d76ed02ece26..ae70ddd878ea9a7f162cd3c7b5746ff9410b47c0 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -15,8 +15,6 @@
 SkGradientShaderBase::SkGradientShaderBase(const Descriptor& desc) {
     SkASSERT(desc.fCount > 1);
 
-    fCacheAlpha = 256;  // init to a value that paint.getAlpha() can't return
-
     fMapper = desc.fMapper;
     SkSafeRef(fMapper);
     fGradFlags = SkToU8(desc.fFlags);
@@ -26,10 +24,6 @@ SkGradientShaderBase::SkGradientShaderBase(const Descriptor& desc) {
     fTileMode = desc.fTileMode;
     fTileProc = gTileProcs[desc.fTileMode];
 
-    fCache16 = fCache16Storage = NULL;
-    fCache32 = NULL;
-    fCache32PixelRef = NULL;
-
     /*  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 dummy entries to ensure that the final data
@@ -144,14 +138,8 @@ static uint32_t unpack_flags(uint32_t packed) {
 }
 
 SkGradientShaderBase::SkGradientShaderBase(SkReadBuffer& buffer) : INHERITED(buffer) {
-    fCacheAlpha = 256;
-
     fMapper = buffer.readUnitMapper();
 
-    fCache16 = fCache16Storage = NULL;
-    fCache32 = NULL;
-    fCache32PixelRef = NULL;
-
     int colorCount = fColorCount = buffer.getArrayCount();
     if (colorCount > kColorStorageCount) {
         size_t allocSize = (sizeof(SkColor) + sizeof(SkPMColor) + sizeof(Rec)) * colorCount;
@@ -186,10 +174,6 @@ SkGradientShaderBase::SkGradientShaderBase(SkReadBuffer& buffer) : INHERITED(buf
 }
 
 SkGradientShaderBase::~SkGradientShaderBase() {
-    if (fCache16Storage) {
-        sk_free(fCache16Storage);
-    }
-    SkSafeUnref(fCache32PixelRef);
     if (fOrigColors != fStorage) {
         sk_free(fOrigColors);
     }
@@ -197,7 +181,6 @@ SkGradientShaderBase::~SkGradientShaderBase() {
 }
 
 void SkGradientShaderBase::initCommon() {
-    fFlags = 0;
     unsigned colorAlpha = 0xFF;
     for (int i = 0; i < fColorCount; i++) {
         colorAlpha &= SkColorGetA(fOrigColors[i]);
@@ -224,6 +207,53 @@ bool SkGradientShaderBase::isOpaque() const {
     return fColorsAreOpaque;
 }
 
+bool SkGradientShaderBase::validContext(const SkBitmap& device, const SkPaint& paint,
+                                        const SkMatrix& matrix, SkMatrix* totalInverse) const {
+    // Make sure we can use totalInverse as a cache.
+    SkMatrix totalInverseLocal;
+    if (NULL == totalInverse) {
+        totalInverse = &totalInverseLocal;
+    }
+
+    if (!this->INHERITED::validContext(device, paint, matrix, totalInverse)) {
+        return false;
+    }
+
+    SkMatrix dstToIndex;
+    return dstToIndex.setConcat(fPtsToUnit, *totalInverse);
+}
+
+size_t SkGradientShaderBase::contextSize() const {

[scroggo, 2014/04/02 20:16:53]

Is it possible to create an SkGradientShaderBase? Is there any reason to
override this?

[Dominik Grewe, 2014/04/03 12:12:59]

No. Removed.

+    return sizeof(GradientShaderBaseContext);
+}
+
+SkGradientShaderBase::GradientShaderBaseContext::GradientShaderBaseContext(
+        const SkGradientShaderBase& shader, const SkBitmap& device,
+        const SkPaint& paint, const SkMatrix& matrix)
+    : INHERITED(shader, device, paint, matrix), fCache(this->getPaintAlpha())

[scroggo, 2014/04/02 20:16:53]

nit: fCache should go on its own line.

[Dominik Grewe, 2014/04/03 12:12:59]

Done.

+{
+    const SkMatrix& inverse = this->getTotalInverse();
+
+    SkAssertResult(fDstToIndex.setConcat(shader.fPtsToUnit, inverse));

[scroggo, 2014/04/02 20:16:53]

I don't think you can assert this result unless you've already called
validContext. (And if I recall correctly, SkBlitter does not call it.)

[Dominik Grewe, 2014/04/03 12:12:59]

The constructor of SkShader::Context asserts that validContext returns true.
(And createContext always calls validContext before creating a context.)

+
+    fDstToIndexProc = fDstToIndex.getMapXYProc();
+    fDstToIndexClass = (uint8_t)SkShader::Context::ComputeMatrixClass(fDstToIndex);
+
+    // now convert our colors in to PMColors
+    unsigned paintAlpha = this->getPaintAlpha();
+
+    fFlags = this->INHERITED::getFlags();
+    if (shader.fColorsAreOpaque && paintAlpha == 0xFF) {
+        fFlags |= kOpaqueAlpha_Flag;
+    }
+    // we can do span16 as long as our individual colors are opaque,
+    // regardless of the paint's alpha
+    if (shader.fColorsAreOpaque) {
+        fFlags |= kHasSpan16_Flag;
+    }
+}
+
+#if 0
 bool SkGradientShaderBase::setContext(const SkBitmap& device,
                                  const SkPaint& paint,
                                  const SkMatrix& matrix) {
@@ -258,20 +288,21 @@ bool SkGradientShaderBase::setContext(const SkBitmap& device,
     this->setCacheAlpha(paintAlpha);
     return true;
 }
+#endif
 
-void SkGradientShaderBase::setCacheAlpha(U8CPU alpha) const {
-    // if the new alpha differs from the previous time we were called, inval our cache
-    // this will trigger the cache to be rebuilt.
-    // we don't care about the first time, since the cache ptrs will already be NULL
-    if (fCacheAlpha != alpha) {
-        fCache16 = NULL;            // inval the cache
-        fCache32 = NULL;            // inval the cache
-        fCacheAlpha = alpha;        // record the new alpha
-        // inform our subclasses
-        if (fCache32PixelRef) {
-            fCache32PixelRef->notifyPixelsChanged();
-        }
-    }
+
+SkGradientShaderBase::GradientShaderCache::GradientShaderCache(U8CPU alpha) {
+    // Invalidate the cache.

[scroggo, 2014/04/02 20:16:53]

I don't think this comment is appropriate, given that this is the constructor
(so there was no cache before this).

[Dominik Grewe, 2014/04/03 12:12:59]

Maybe "invalidate" is the wrong term, but I wanted to say that the cache isn't
initialized yet. I'll update the comment and add another on the class
definition.

+    fCache16 = NULL;
+    fCache32 = NULL;
+    fCache16Storage = NULL;
+    fCache32PixelRef = NULL;
+    fCacheAlpha = alpha;
+}
+
+SkGradientShaderBase::GradientShaderCache::~GradientShaderCache() {
+    sk_free(fCache16Storage);
+    SkSafeUnref(fCache32PixelRef);
 }
 
 #define Fixed_To_Dot8(x)        (((x) + 0x80) >> 8)
@@ -280,8 +311,8 @@ void SkGradientShaderBase::setCacheAlpha(U8CPU alpha) const {
     build a 16bit table as long as the original colors are opaque, even if the
     paint specifies a non-opaque alpha.
 */
-void SkGradientShaderBase::Build16bitCache(uint16_t cache[], SkColor c0, SkColor c1,
-                                      int count) {
+void SkGradientShaderBase::GradientShaderCache::Build16bitCache(
+        uint16_t cache[], SkColor c0, SkColor c1, int count) {
     SkASSERT(count > 1);
     SkASSERT(SkColorGetA(c0) == 0xFF);
     SkASSERT(SkColorGetA(c1) == 0xFF);
@@ -329,8 +360,9 @@ void SkGradientShaderBase::Build16bitCache(uint16_t cache[], SkColor c0, SkColor
  */
 typedef uint32_t SkUFixed;
 
-void SkGradientShaderBase::Build32bitCache(SkPMColor cache[], SkColor c0, SkColor c1,
-                                      int count, U8CPU paintAlpha, uint32_t gradFlags) {
+void SkGradientShaderBase::GradientShaderCache::Build32bitCache(
+        SkPMColor cache[], SkColor c0, SkColor c1,
+        int count, U8CPU paintAlpha, uint32_t gradFlags) {
     SkASSERT(count > 1);
 
     // need to apply paintAlpha to our two endpoints
@@ -473,7 +505,8 @@ static inline U16CPU bitsTo16(unsigned x, const unsigned bits) {
     return 0;
 }
 
-const uint16_t* SkGradientShaderBase::getCache16() const {
+const uint16_t* SkGradientShaderBase::GradientShaderCache::getCache16(
+        const SkGradientShaderBase& shader) {
     if (fCache16 == NULL) {
         // double the count for dither entries
         const int entryCount = kCache16Count * 2;
@@ -483,27 +516,28 @@ const uint16_t* SkGradientShaderBase::getCache16() const {
             fCache16Storage = (uint16_t*)sk_malloc_throw(allocSize);
         }
         fCache16 = fCache16Storage;
-        if (fColorCount == 2) {
-            Build16bitCache(fCache16, fOrigColors[0], fOrigColors[1],
+        if (shader.fColorCount == 2) {
+            Build16bitCache(fCache16, shader.fOrigColors[0], shader.fOrigColors[1],
                             kCache16Count);
         } else {
-            Rec* rec = fRecs;
+            Rec* rec = shader.fRecs;
             int prevIndex = 0;
-            for (int i = 1; i < fColorCount; i++) {
+            for (int i = 1; i < shader.fColorCount; i++) {
                 int nextIndex = SkFixedToFFFF(rec[i].fPos) >> kCache16Shift;
                 SkASSERT(nextIndex < kCache16Count);
 
                 if (nextIndex > prevIndex)
-                    Build16bitCache(fCache16 + prevIndex, fOrigColors[i-1], fOrigColors[i], nextIndex - prevIndex + 1);
+                    Build16bitCache(fCache16 + prevIndex, shader.fOrigColors[i-1],
+                                    shader.fOrigColors[i], nextIndex - prevIndex + 1);
                 prevIndex = nextIndex;
             }
         }
 
-        if (fMapper) {
+        if (shader.fMapper) {
             fCache16Storage = (uint16_t*)sk_malloc_throw(allocSize);
             uint16_t* linear = fCache16;         // just computed linear data
             uint16_t* mapped = fCache16Storage;  // storage for mapped data
-            SkUnitMapper* map = fMapper;
+            SkUnitMapper* map = shader.fMapper;
             for (int i = 0; i < kCache16Count; i++) {
                 int index = map->mapUnit16(bitsTo16(i, kCache16Bits)) >> kCache16Shift;
                 mapped[i] = linear[index];
@@ -516,7 +550,8 @@ const uint16_t* SkGradientShaderBase::getCache16() const {
     return fCache16;
 }
 
-const SkPMColor* SkGradientShaderBase::getCache32() const {
+const SkPMColor* SkGradientShaderBase::GradientShaderCache::getCache32(
+        const SkGradientShaderBase& shader) {
     if (fCache32 == NULL) {
         SkImageInfo info;
         info.fWidth = kCache32Count;
@@ -528,29 +563,29 @@ const SkPMColor* SkGradientShaderBase::getCache32() const {
             fCache32PixelRef = SkMallocPixelRef::NewAllocate(info, 0, NULL);
         }
         fCache32 = (SkPMColor*)fCache32PixelRef->getAddr();
-        if (fColorCount == 2) {
-            Build32bitCache(fCache32, fOrigColors[0], fOrigColors[1],
-                            kCache32Count, fCacheAlpha, fGradFlags);
+        if (shader.fColorCount == 2) {
+            Build32bitCache(fCache32, shader.fOrigColors[0], shader.fOrigColors[1],
+                            kCache32Count, fCacheAlpha, shader.fGradFlags);
         } else {
-            Rec* rec = fRecs;
+            Rec* rec = shader.fRecs;
             int prevIndex = 0;
-            for (int i = 1; i < fColorCount; i++) {
+            for (int i = 1; i < shader.fColorCount; i++) {
                 int nextIndex = SkFixedToFFFF(rec[i].fPos) >> kCache32Shift;
                 SkASSERT(nextIndex < kCache32Count);
 
                 if (nextIndex > prevIndex)
-                    Build32bitCache(fCache32 + prevIndex, fOrigColors[i-1],
-                                    fOrigColors[i], nextIndex - prevIndex + 1,
-                                    fCacheAlpha, fGradFlags);
+                    Build32bitCache(fCache32 + prevIndex, shader.fOrigColors[i-1],
+                                    shader.fOrigColors[i], nextIndex - prevIndex + 1,
+                                    fCacheAlpha, shader.fGradFlags);
                 prevIndex = nextIndex;
             }
         }
 
-        if (fMapper) {
+        if (shader.fMapper) {
             SkMallocPixelRef* newPR = SkMallocPixelRef::NewAllocate(info, 0, NULL);
             SkPMColor* linear = fCache32;           // just computed linear data
             SkPMColor* mapped = (SkPMColor*)newPR->getAddr();    // storage for mapped data
-            SkUnitMapper* map = fMapper;
+            SkUnitMapper* map = shader.fMapper;
             for (int i = 0; i < kCache32Count; i++) {
                 int index = map->mapUnit16((i << 8) | i) >> 8;
                 mapped[i + kCache32Count*0] = linear[index + kCache32Count*0];
@@ -577,14 +612,14 @@ const SkPMColor* SkGradientShaderBase::getCache32() const {
 void SkGradientShaderBase::getGradientTableBitmap(SkBitmap* bitmap) const {
     // our caller assumes no external alpha, so we ensure that our cache is
     // built with 0xFF
-    this->setCacheAlpha(0xFF);
+    GradientShaderCache cache(0xFF);
 
     // don't have a way to put the mapper into our cache-key yet
     if (fMapper) {
         // force our cahce32pixelref to be built
-        (void)this->getCache32();
+        (void)cache.getCache32(*this);
         bitmap->setConfig(SkImageInfo::MakeN32Premul(kCache32Count, 1));
-        bitmap->setPixelRef(fCache32PixelRef);
+        bitmap->setPixelRef(cache.getCache32PixelRef());
         return;
     }
 
@@ -623,9 +658,9 @@ void SkGradientShaderBase::getGradientTableBitmap(SkBitmap* bitmap) const {
 
     if (!gCache->find(storage.get(), size, bitmap)) {
         // force our cahce32pixelref to be built
-        (void)this->getCache32();
+        (void)cache.getCache32(*this);
         bitmap->setConfig(SkImageInfo::MakeN32Premul(kCache32Count, 1));
-        bitmap->setPixelRef(fCache32PixelRef);
+        bitmap->setPixelRef(cache.getCache32PixelRef());
 
         gCache->add(storage.get(), size, *bitmap);
     }