add shader flag kConstInY_Flag

this signals blitters that the shader will return the same results for a given
x value, independent of y. Useful inside blitRect(), where it can cache the
first call to shadeSpan() and reuse it on all subsequent scans. Works with
(non-rotated) linear-gradients, and Nx1 bitmaps.



git-svn-id: http://skia.googlecode.com/svn/trunk@214 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 11 insertions, 0 deletions

diff --git a/src/core/SkBitmapProcShader.cpp b/src/core/SkBitmapProcShader.cpp
index 8ba57c4ae3..2302e0f048 100644
--- a/src/core/SkBitmapProcShader.cpp
+++ b/src/core/SkBitmapProcShader.cpp
@@ -67,6 +67,11 @@ void SkBitmapProcShader::flatten(SkFlattenableWriteBuffer& buffer) {
     buffer.write8(fState.fTileModeY);
 }
 
+static bool only_scale_and_translate(const SkMatrix& matrix) {
+    unsigned mask = SkMatrix::kTranslate_Mask | SkMatrix::kScale_Mask;
+    return (matrix.getType() & ~mask) == 0;
+}
+
 bool SkBitmapProcShader::setContext(const SkBitmap& device,
                                     const SkPaint& paint,
                                     const SkMatrix& matrix) {
@@ -117,6 +122,12 @@ bool SkBitmapProcShader::setContext(const SkBitmap& device,
         default:
             break;
     }
+
+    // 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())) {
+        fFlags |= kConstInY_Flag;
+    }
     return true;
 }