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update comment on setShader to clarify alpha-bitmap behavior in bitmapshaders

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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
This commit is contained in:
commit-bot@chromium.org 2014-03-18 16:28:12 +00:00
parent 14bdd527ee
commit e5957f67d0
2 changed files with 24 additions and 21 deletions
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38
gm/bitmapshader.cpp
View File

@ -35,6 +35,11 @@ static void draw_mask(SkBitmap* bm) {
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 @@ protected:
}
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:

7
include/core/SkPaint.h
View File

@ -514,7 +514,12 @@ public:
* 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.