update comment on setShader to clarify alpha-bitmap behavior in bitmapshaders
BUG=skia:2293
R=bsalomon@google.com, yunchao.he@intel.com
Author: reed@google.com
Review URL: https://codereview.chromium.org/203203005
git-svn-id: http://skia.googlecode.com/svn/trunk@13851 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gm/bitmapshader.cpp b/gm/bitmapshader.cpp
index 4649b7e..fb56307 100644
--- a/gm/bitmapshader.cpp
+++ b/gm/bitmapshader.cpp
@@ -35,6 +35,11 @@
canvas.drawCircle(10, 10, 10, circlePaint);
}
+static void adopt_shader(SkPaint* paint, SkShader* shader) {
+ paint->setShader(shader);
+ SkSafeUnref(shader);
+}
+
class BitmapShaderGM : public GM {
public:
@@ -50,40 +55,33 @@
}
virtual SkISize onISize() {
- return make_isize(75, 100);
+ return SkISize::Make(75, 100);
}
virtual void onDraw(SkCanvas* canvas) {
- SkShader* shader = SkShader::CreateBitmapShader(fBitmap,
- SkShader::kClamp_TileMode,
- SkShader::kClamp_TileMode);
SkPaint paint;
- paint.setShader(shader);
- // release the shader ref as the paint now holds a reference
- shader->unref();
+
+ adopt_shader(&paint, SkShader::CreateBitmapShader(fBitmap, SkShader::kClamp_TileMode,
+ SkShader::kClamp_TileMode));
// draw the shader with a bitmap mask
canvas->drawBitmap(fMask, 0, 0, &paint);
canvas->drawBitmap(fMask, 30, 0, &paint);
- canvas->translate(0, 25);
+ canvas->translate(0, 25);
- // draw the shader with standard geometry
- canvas->drawCircle(10, 10, 10, paint);
- canvas->drawCircle(40, 10, 10, paint); // no blue circle expected
+ canvas->drawCircle(10, 10, 10, paint);
+ canvas->drawCircle(40, 10, 10, paint); // no blue circle expected
- canvas->translate(0, 25);
+ canvas->translate(0, 25);
- shader = SkShader::CreateBitmapShader(fMask,
- SkShader::kRepeat_TileMode,
- SkShader::kRepeat_TileMode);
- paint.setShader(shader);
+ adopt_shader(&paint, SkShader::CreateBitmapShader(fMask, SkShader::kRepeat_TileMode,
+ SkShader::kRepeat_TileMode));
paint.setColor(SK_ColorRED);
- shader->unref();
- // draw the mask using the shader and a color
- canvas->drawRect(SkRect::MakeXYWH(0, 0, 20, 20), paint);
- canvas->drawRect(SkRect::MakeXYWH(30, 0, 20, 20), paint);
+ // draw the mask using the shader and a color
+ canvas->drawRect(SkRect::MakeXYWH(0, 0, 20, 20), paint);
+ canvas->drawRect(SkRect::MakeXYWH(30, 0, 20, 20), paint);
}
private:
diff --git a/include/core/SkPaint.h b/include/core/SkPaint.h
index d1853c6..e86d011 100644
--- a/include/core/SkPaint.h
+++ b/include/core/SkPaint.h
@@ -514,7 +514,12 @@
* once (e.g. bitmap tiling or gradient) and then change its transparency
* w/o having to modify the original shader... only the paint's alpha needs
* to be modified.
- * <p />
+ *
+ * There is an exception to this only-respect-paint's-alpha rule: If the shader only generates
+ * alpha (e.g. SkShader::CreateBitmapShader(bitmap, ...) where bitmap's colortype is kAlpha_8)
+ * then the shader will use the paint's entire color to "colorize" its output (modulating the
+ * bitmap's alpha with the paint's color+alpha).
+ *
* Pass NULL to clear any previous shader.
* As a convenience, the parameter passed is also returned.
* If a previous shader exists, its reference count is decremented.