expand SkShader's flag kConstInY to 16 and 32 variants, allowing a shader

(like gradients) to support predithering. If they do, then they would suppress
kConstInY16, since they no longer are const.

The blitters now check for each flag separately, so we don't have to give up
const-in-Y in the 32bit case, since in that mode we don't care about dithering.



git-svn-id: http://skia.googlecode.com/svn/trunk@339 2bbb7eff-a529-9590-31e7-b0007b416f81

6 files changed, 82 insertions, 118 deletions

diff --git a/include/core/SkShader.h b/include/core/SkShader.h
index 8fac8cbb08..f3d4856b3a 100644
--- a/include/core/SkShader.h
+++ b/include/core/SkShader.h
@@ -62,10 +62,10 @@ public:
 
     enum Flags {
         //!< set if all of the colors will be opaque
-        kOpaqueAlpha_Flag   = 0x01,
+        kOpaqueAlpha_Flag  = 0x01,
 
         //! set if this shader's shadeSpan16() method can be called
-        kHasSpan16_Flag     = 0x02,
+        kHasSpan16_Flag = 0x02,
 
         /** Set this bit if the shader's native data type is instrinsically 16
             bit, meaning that calling the 32bit shadeSpan() entry point will
@@ -76,9 +76,17 @@ public:
 
         /** set (after setContext) if the spans only vary in X (const in Y).
             e.g. an Nx1 bitmap that is being tiled in Y, or a linear-gradient
-            that varies from left-to-right
+            that varies from left-to-right. This flag specifies this for
+            shadeSpan().
          */
-        kConstInY_Flag = 0x08
+        kConstInY32_Flag = 0x08,
+        
+        /** same as kConstInY32_Flag, but is set if this is true for shadeSpan16
+            which may not always be the case, since shadeSpan16 may be
+            predithered, which would mean it was not const in Y, even though
+            the 32bit shadeSpan() would be const.
+         */
+        kConstInY16_Flag = 0x10
     };
 
     /** Called sometimes before drawing with this shader.
@@ -99,29 +107,28 @@ public:
         parameters, or false if not. If false is returned, nothing
         will be drawn.
     */
-    virtual bool    setContext( const SkBitmap& device,
-                                const SkPaint& paint,
-                                const SkMatrix& matrix);
+    virtual bool setContext(const SkBitmap& device, const SkPaint& paint,
+                            const SkMatrix& matrix);
 
     /** Called for each span of the object being drawn. Your subclass
         should set the appropriate colors (with premultiplied alpha) that
         correspond to the specified device coordinates.
     */
-    virtual void    shadeSpan(int x, int y, SkPMColor[], int count) = 0;
-    /** Called only for 16bit devices when getFlags() returns kOpaqueAlphaFlag | kHasSpan16_Flag
+    virtual void shadeSpan(int x, int y, SkPMColor[], int count) = 0;
+    /** Called only for 16bit devices when getFlags() returns
+        kOpaqueAlphaFlag | kHasSpan16_Flag
     */
-    virtual void    shadeSpan16(int x, int y, uint16_t[], int count);
+    virtual void shadeSpan16(int x, int y, uint16_t[], int count);
     /** Similar to shadeSpan, but only returns the alpha-channel for a span.
         The default implementation calls shadeSpan() and then extracts the alpha
         values from the returned colors.
     */
-    virtual void    shadeSpanAlpha(int x, int y, uint8_t alpha[], int count);
+    virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count);
 
     /** Helper function that returns true if this shader's shadeSpan16() method can
         be called.
     */
-    bool canCallShadeSpan16()
-    {
+    bool canCallShadeSpan16() {
         return SkShader::CanCallShadeSpan16(this->getFlags());
     }
 
diff --git a/samplecode/SampleDitherBitmap.cpp b/samplecode/SampleDitherBitmap.cpp
index e859cdaf44..1000fdfaa0 100644
--- a/samplecode/SampleDitherBitmap.cpp
+++ b/samplecode/SampleDitherBitmap.cpp
@@ -1,9 +1,35 @@
 #include "SampleCode.h"
 #include "SkColorPriv.h"
+#include "SkGradientShader.h"
 #include "SkView.h"
 #include "SkCanvas.h"
 #include "SkUtils.h"
 
+static void draw_rect(SkCanvas* canvas, const SkRect& r, const SkPaint& p) {
+    canvas->drawRect(r, p);
+
+    SkPaint frame(p);
+    frame.setShader(NULL);
+    frame.setStyle(SkPaint::kStroke_Style);
+    canvas->drawRect(r, frame);
+}
+
+static void draw_gradient(SkCanvas* canvas) {
+    SkRect r = { 0, 0, SkIntToScalar(256), SkIntToScalar(32) };
+    SkPoint pts[] = { r.fLeft, r.fTop, r.fRight, r.fTop };
+    SkColor colors[] = { 0xFF000000, 0xFFFF0000 };
+    SkShader* s = SkGradientShader::CreateLinear(pts, colors, NULL, 2,
+                                                 SkShader::kClamp_TileMode);
+
+    SkPaint p;
+    p.setShader(s)->unref();
+    draw_rect(canvas, r, p);
+
+    canvas->translate(0, SkIntToScalar(40));
+    p.setDither(true);
+    draw_rect(canvas, r, p);
+}
+
 static void test_pathregion() {
     SkPath path;
     SkRegion region;
@@ -103,6 +129,9 @@ protected:
         draw2(canvas, fBM8);
         canvas->translate(0, SkIntToScalar(fBM8.height() *3));
         draw2(canvas, fBM32);
+
+        canvas->translate(0, SkIntToScalar(fBM8.height() *3));
+        draw_gradient(canvas);
     }
     
 private:
diff --git a/src/core/SkBitmapProcShader.cpp b/src/core/SkBitmapProcShader.cpp
index cb4d129d5b..a8e21b4f5f 100644
--- a/src/core/SkBitmapProcShader.cpp
+++ b/src/core/SkBitmapProcShader.cpp
@@ -132,7 +132,10 @@ bool SkBitmapProcShader::setContext(const SkBitmap& device,
     // if we're only 1-pixel heigh, and we don't rotate, then we can claim this
     if (1 == fState.fBitmap->height() &&
             only_scale_and_translate(this->getTotalInverse())) {
-        flags |= kConstInY_Flag;
+        flags |= kConstInY32_Flag;
+        if (flags & kHasSpan16_Flag) {
+            flags |= kConstInY16_Flag;
+        }
     }
 
     fFlags = flags;
diff --git a/src/core/SkBlitter_RGB16.cpp b/src/core/SkBlitter_RGB16.cpp
index c41efef0a5..ac6b5d0bbf 100644
--- a/src/core/SkBlitter_RGB16.cpp
+++ b/src/core/SkBlitter_RGB16.cpp
@@ -528,7 +528,7 @@ void SkRGB16_Shader16_Blitter::blitRect(int x, int y, int width, int height) {
     int         alpha = shader->getSpan16Alpha();
 
     if (0xFF == alpha) {
-        if (fShaderFlags & SkShader::kConstInY_Flag) {
+        if (fShaderFlags & SkShader::kConstInY16_Flag) {
             // have the shader blit directly into the device the first time
             shader->shadeSpan16(x, y, dst, width);
             // and now just memcpy that line on the subsequent lines
@@ -549,7 +549,7 @@ void SkRGB16_Shader16_Blitter::blitRect(int x, int y, int width, int height) {
     } else {
         int scale = SkAlpha255To256(alpha);
         uint16_t* span16 = (uint16_t*)fBuffer;
-        if (fShaderFlags & SkShader::kConstInY_Flag) {
+        if (fShaderFlags & SkShader::kConstInY16_Flag) {
             shader->shadeSpan16(x, y, span16, width);
             do {
                 SkBlendRGB16(span16, dst, scale, width);
@@ -668,7 +668,7 @@ void SkRGB16_Shader_Blitter::blitRect(int x, int y, int width, int height) {
     uint16_t*       dst = fDevice.getAddr16(x, y);
     size_t          dstRB = fDevice.rowBytes();
 
-    if (fShaderFlags & SkShader::kConstInY_Flag) {
+    if (fShaderFlags & SkShader::kConstInY32_Flag) {
         shader->shadeSpan(x, y, buffer, width);
         do {
             proc(dst, buffer, width, 0xFF, x, y);
diff --git a/src/core/SkShader.cpp b/src/core/SkShader.cpp
index 5567914530..5290f2ff0a 100644
--- a/src/core/SkShader.cpp
+++ b/src/core/SkShader.cpp
@@ -263,7 +263,7 @@ bool SkColorShader::setContext(const SkBitmap& device, const SkPaint& paint,
     }
     fPMColor = SkPackARGB32(a, r, g, b);
 
-    fFlags = kHasSpan16_Flag | kConstInY_Flag;
+    fFlags = kHasSpan16_Flag | kConstInY32_Flag;
     if (SkGetPackedA32(fPMColor) == 255) {
         fFlags |= kOpaqueAlpha_Flag;
     }
diff --git a/src/effects/SkGradientShader.cpp b/src/effects/SkGradientShader.cpp
index 635e0e579f..860e902dd2 100644
--- a/src/effects/SkGradientShader.cpp
+++ b/src/effects/SkGradientShader.cpp
@@ -20,18 +20,6 @@
 #include "SkUnitMapper.h"
 #include "SkUtils.h"
 
-/*
-    ToDo
-
-    - not sure we still need the full Rec struct, now that we're using a cache
-    - detect const-alpha (but not opaque) in getFlags()
-*/
-
-/* dither seems to look better, but not stuningly yet, and it slows us down a little
-    so its not on by default yet.
-*/
-#define TEST_GRADIENT_DITHER
-
 ///////////////////////////////////////////////////////////////////////////
 
 typedef SkFixed (*TileProc)(SkFixed);
@@ -503,12 +491,9 @@ static inline U16CPU dot6to16(unsigned x) {
 
 const uint16_t* Gradient_Shader::getCache16() {
     if (fCache16 == NULL) {
-        if (fCache16Storage == NULL) // set the storage and our working ptr
-#ifdef TEST_GRADIENT_DITHER
+        if (fCache16Storage == NULL) { // set the storage and our working ptr
             fCache16Storage = (uint16_t*)sk_malloc_throw(sizeof(uint16_t) * kCache16Count * 2);
-#else
-            fCache16Storage = (uint16_t*)sk_malloc_throw(sizeof(uint16_t) * kCache16Count);
-#endif
+        }
         fCache16 = fCache16Storage;
         if (fColorCount == 2) {
             build_16bit_cache(fCache16, fOrigColors[0], fOrigColors[1], kCache16Count);
@@ -527,20 +512,14 @@ const uint16_t* Gradient_Shader::getCache16() {
         }
 
         if (fMapper) {
-#ifdef TEST_GRADIENT_DITHER
             fCache16Storage = (uint16_t*)sk_malloc_throw(sizeof(uint16_t) * kCache16Count * 2);
-#else
-            fCache16Storage = (uint16_t*)sk_malloc_throw(sizeof(uint16_t) * kCache16Count);
-#endif
             uint16_t* linear = fCache16;         // just computed linear data
             uint16_t* mapped = fCache16Storage;  // storage for mapped data
             SkUnitMapper* map = fMapper;
             for (int i = 0; i < 64; i++) {
                 int index = map->mapUnit16(dot6to16(i)) >> 10;
                 mapped[i] = linear[index];
-#ifdef TEST_GRADIENT_DITHER
                 mapped[i + 64] = linear[index + 64];
-#endif
             }
             sk_free(fCache16);
             fCache16 = fCache16Storage;
@@ -655,7 +634,13 @@ bool Linear_Gradient::setContext(const SkBitmap& device, const SkPaint& paint,
 
     unsigned mask = SkMatrix::kTranslate_Mask | SkMatrix::kScale_Mask;
     if ((fDstToIndex.getType() & ~mask) == 0) {
-        fFlags |= SkShader::kConstInY_Flag;
+        fFlags |= SkShader::kConstInY32_Flag;
+        if ((fFlags & SkShader::kHasSpan16_Flag) && !paint.isDither()) {
+            // only claim this if we do have a 16bit mode (i.e. none of our
+            // colors have alpha), and if we are not dithering (which obviously
+            // is not const in Y).
+            fFlags |= SkShader::kConstInY16_Flag;
+        }
     }
     return true;
 }
@@ -779,11 +764,9 @@ bool Linear_Gradient::asABitmap(SkBitmap* bitmap, SkMatrix* matrix,
     return true;
 }
 
-#ifdef TEST_GRADIENT_DITHER
-static void dither_memset16(uint16_t dst[], uint16_t value, uint16_t other, int count)
-{
-    if (reinterpret_cast<uintptr_t>(dst) & 2)
-    {
+static void dither_memset16(uint16_t dst[], uint16_t value, uint16_t other,
+                            int count) {
+    if (reinterpret_cast<uintptr_t>(dst) & 2) {
         *dst++ = value;
         count -= 1;
         SkTSwap(value, other);
@@ -791,10 +774,10 @@ static void dither_memset16(uint16_t dst[], uint16_t value, uint16_t other, int
 
     sk_memset32((uint32_t*)dst, (value << 16) | other, count >> 1);
     
-    if (count & 1)
+    if (count & 1) {
         dst[count - 1] = value;
+    }
 }
-#endif
 
 void Linear_Gradient::shadeSpan16(int x, int y, uint16_t dstC[], int count)
 {
@@ -804,9 +787,7 @@ void Linear_Gradient::shadeSpan16(int x, int y, uint16_t dstC[], int count)
     SkMatrix::MapXYProc dstProc = fDstToIndexProc;
     TileProc            proc = fTileProc;
     const uint16_t*     cache = this->getCache16();
-#ifdef TEST_GRADIENT_DITHER
     int                 toggle = ((x ^ y) & 1) << kCache16Bits;
-#endif
 
     if (fDstToIndexClass != kPerspective_MatrixClass) {
         dstProc(fDstToIndex, SkIntToScalar(x), SkIntToScalar(y), &srcPt);
@@ -827,34 +808,22 @@ void Linear_Gradient::shadeSpan16(int x, int y, uint16_t dstC[], int count)
             // we're a vertical gradient, so no change in a span
             unsigned fi = proc(fx) >> 10;
             SkASSERT(fi <= 63);
-#ifdef TEST_GRADIENT_DITHER
             dither_memset16(dstC, cache[toggle + fi], cache[(toggle ^ (1 << kCache16Bits)) + fi], count);
-#else
-            sk_memset16(dstC, cache[fi], count);
-#endif
         } else if (proc == clamp_tileproc) {
             do {
                 unsigned fi = SkClampMax(fx >> 10, 63);
                 SkASSERT(fi <= 63);
                 fx += dx;
-#ifdef TEST_GRADIENT_DITHER
                 *dstC++ = cache[toggle + fi];
                 toggle ^= (1 << kCache16Bits);
-#else
-                *dstC++ = cache[fi];
-#endif
             } while (--count != 0);
         } else if (proc == mirror_tileproc) {
             do {
                 unsigned fi = mirror_6bits(fx >> 10);
                 SkASSERT(fi <= 0x3F);
                 fx += dx;
-#ifdef TEST_GRADIENT_DITHER
                 *dstC++ = cache[toggle + fi];
                 toggle ^= (1 << kCache16Bits);
-#else
-                *dstC++ = cache[fi];
-#endif
             } while (--count != 0);
         } else {
             SkASSERT(proc == repeat_tileproc);
@@ -862,12 +831,8 @@ void Linear_Gradient::shadeSpan16(int x, int y, uint16_t dstC[], int count)
                 unsigned fi = repeat_6bits(fx >> 10);
                 SkASSERT(fi <= 0x3F);
                 fx += dx;
-#ifdef TEST_GRADIENT_DITHER
                 *dstC++ = cache[toggle + fi];
                 toggle ^= (1 << kCache16Bits);
-#else
-                *dstC++ = cache[fi];
-#endif
             } while (--count != 0);
         }
     } else {
@@ -879,12 +844,8 @@ void Linear_Gradient::shadeSpan16(int x, int y, uint16_t dstC[], int count)
             SkASSERT(fi <= 0xFFFF);
 
             int index = fi >> (16 - kCache16Bits);
-#ifdef TEST_GRADIENT_DITHER
             *dstC++ = cache[toggle + index];
             toggle ^= (1 << kCache16Bits);
-#else
-            *dstC++ = cache[index];
-#endif
 
             dstX += SK_Scalar1;
         } while (--count != 0);
@@ -1033,40 +994,33 @@ public:
             } while (--count != 0);
         }
     }
-    virtual void shadeSpan16(int x, int y, uint16_t dstC[], int count)
-    {
+
+    virtual void shadeSpan16(int x, int y, uint16_t dstC[], int count) {
         SkASSERT(count > 0);
 
         SkPoint             srcPt;
         SkMatrix::MapXYProc dstProc = fDstToIndexProc;
         TileProc            proc = fTileProc;
         const uint16_t*     cache = this->getCache16();
-#ifdef TEST_GRADIENT_DITHER
         int                 toggle = ((x ^ y) & 1) << kCache16Bits;
-#endif
 
-        if (fDstToIndexClass != kPerspective_MatrixClass)
-        {
+        if (fDstToIndexClass != kPerspective_MatrixClass) {
             dstProc(fDstToIndex, SkIntToScalar(x), SkIntToScalar(y), &srcPt);
             SkFixed dx, fx = SkScalarToFixed(srcPt.fX);
             SkFixed dy, fy = SkScalarToFixed(srcPt.fY);
 
-            if (fDstToIndexClass == kFixedStepInX_MatrixClass)
-            {
+            if (fDstToIndexClass == kFixedStepInX_MatrixClass) {
                 SkFixed storage[2];
                 (void)fDstToIndex.fixedStepInX(SkIntToScalar(y), &storage[0], &storage[1]);
                 dx = storage[0];
                 dy = storage[1];
-            }
-            else
-            {
+            } else {
                 SkASSERT(fDstToIndexClass == kLinear_MatrixClass);
                 dx = SkScalarToFixed(fDstToIndex.getScaleX());
                 dy = SkScalarToFixed(fDstToIndex.getSkewY());
             }
 
-            if (proc == clamp_tileproc)
-            {
+            if (proc == clamp_tileproc) {
                 const uint8_t* sqrt_table = gSqrt8Table;
 
                 /* knock these down so we can pin against +- 0x7FFF, which is an immediate load,
@@ -1079,8 +1033,7 @@ public:
                 dx >>= 1;
                 fy >>= 1;
                 dy >>= 1;
-                if (dy == 0)    // might perform this check for the other modes, but the win will be a smaller % of the total
-                {
+                if (dy == 0) {    // might perform this check for the other modes, but the win will be a smaller % of the total
                     fy = SkPin32(fy, -0xFFFF >> 1, 0xFFFF >> 1);
                     fy *= fy;
                     do {
@@ -1088,16 +1041,10 @@ public:
                         unsigned fi = (xx * xx + fy) >> (14 + 16 - kSQRT_TABLE_BITS);
                         fi = SkFastMin32(fi, 0xFFFF >> (16 - kSQRT_TABLE_BITS));
                         fx += dx;
-#ifdef TEST_GRADIENT_DITHER
                         *dstC++ = cache[toggle + (sqrt_table[fi] >> (8 - kCache16Bits))];
                         toggle ^= (1 << kCache16Bits);
-#else
-                        *dstC++ = cache[sqrt_table[fi] >> (8 - kCache16Bits)];
-#endif
                     } while (--count != 0);
-                }
-                else
-                {
+                } else {
                     do {
                         unsigned xx = SkPin32(fx, -0xFFFF >> 1, 0xFFFF >> 1);
                         unsigned fi = SkPin32(fy, -0xFFFF >> 1, 0xFFFF >> 1);
@@ -1105,33 +1052,21 @@ public:
                         fi = SkFastMin32(fi, 0xFFFF >> (16 - kSQRT_TABLE_BITS));
                         fx += dx;
                         fy += dy;
-#ifdef TEST_GRADIENT_DITHER
                         *dstC++ = cache[toggle + (sqrt_table[fi] >> (8 - kCache16Bits))];
                         toggle ^= (1 << kCache16Bits);
-#else
-                        *dstC++ = cache[sqrt_table[fi] >> (8 - kCache16Bits)];
-#endif
                     } while (--count != 0);
                 }
-            }
-            else if (proc == mirror_tileproc)
-            {
+            } else if (proc == mirror_tileproc) {
                 do {
                     SkFixed dist = SkFixedSqrt(SkFixedSquare(fx) + SkFixedSquare(fy));
                     unsigned fi = mirror_tileproc(dist);
                     SkASSERT(fi <= 0xFFFF);
                     fx += dx;
                     fy += dy;
-#ifdef TEST_GRADIENT_DITHER
                     *dstC++ = cache[toggle + (fi >> (16 - kCache16Bits))];
                     toggle ^= (1 << kCache16Bits);
-#else
-                    *dstC++ = cache[fi >> (16 - kCache16Bits)];
-#endif
                 } while (--count != 0);
-            }
-            else
-            {
+            } else {
                 SkASSERT(proc == repeat_tileproc);
                 do {
                     SkFixed dist = SkFixedSqrt(SkFixedSquare(fx) + SkFixedSquare(fy));
@@ -1139,17 +1074,11 @@ public:
                     SkASSERT(fi <= 0xFFFF);
                     fx += dx;
                     fy += dy;
-#ifdef TEST_GRADIENT_DITHER
                     *dstC++ = cache[toggle + (fi >> (16 - kCache16Bits))];
                     toggle ^= (1 << kCache16Bits);
-#else
-                    *dstC++ = cache[fi >> (16 - kCache16Bits)];
-#endif
                 } while (--count != 0);
             }
-        }
-        else    // perspective case
-        {
+        } else {    // perspective case
             SkScalar dstX = SkIntToScalar(x);
             SkScalar dstY = SkIntToScalar(y);
             do {
@@ -1158,12 +1087,8 @@ public:
                 SkASSERT(fi <= 0xFFFF);
 
                 int index = fi >> (16 - kCache16Bits);
-#ifdef TEST_GRADIENT_DITHER
                 *dstC++ = cache[toggle + index];
                 toggle ^= (1 << kCache16Bits);
-#else
-                *dstC++ = cache[index];
-#endif
 
                 dstX += SK_Scalar1;
             } while (--count != 0);