The problem of drawing gradient effect

[becky]

I use skia to draw large rectangle with gradient effect, however, the
effect is not natural.
when the rectangle is small, the effect is good.

why?? do I use the API wrong?

Code is as follows.

SkPoint center;
center.set(160,240);
SkColor color[2];
color[0]=SkColorSetARGB(255,0,0,0);
color[1]=SkColorSetARGB(255,255,255,255);
SkShader *sh=SkGradientShader::CreateRadial(center,100,color,NULL,
2,SkShader::kClamp_TileMode,NULL);
SkPaint paint;
paint.setShader(sh);
SkRect r;
r.set(0, 0, 320, 480);
canv->drawRect(r, paint);

[Elliot Poger]

Becky, can you please attach images showing the large rectangle and the small one (showing one with "good" effect and another with "unnatural" effect)?

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[旭赵]

the big_gradient_skia_effect.png is the skia drawing effect on large rectangle, and the gradient color is with transparent 20%. and the big_gradient_origina_effect.png is the original effect. This effect is very poor compared to the original.

the small_gradient_skia_effect.png is the skia drawing effect on small rectangle, and the gradient color is with transparent 100%. the effect is ok.

by the way,I use skia to draw on android phone.

[Elliot Poger]

Becky, I'm a bit confused by the example you sent.  (I'm not sure which of those images was generated with the code snippet you sent, or where the "original" image came from.)

I have created a local modification to our "gradient" gm test that is based on your code snippet and generates rectangles of various sizes.

I am attaching here the code patch and the resulting image files I got when I ran it on Linux.  Here's how you can generate the images yourself using the patch...

cd .../trunk

patch -p0 <patch.txt

make -j gm

mkdir -p out/my-gm-images

out/Debug/gm -w out/my-gm-images

eog out/my-gm-images/gradient_sizes_*.png &

Can you please point out to me what about these images seems wrong to you?  Or modify the patch so that it DOES demonstrate the problem?