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I am drawing some textures with alpha channel, but when they are displayed it looks like the alpha channel is only binary. So a pixel is either transparent or opaque, although in the texture file itself the pixel is half-transparent. The blending is set up like this:

gl.glEnable(GL10.GL_BLEND);
gl.glBlendFunc(GL10.GL_ONE, GL10.GL_ONE_MINUS_SRC_ALPHA);

Is there a workaround for this problem?

The above shows how it should be like, and the below shows how it is:

alt text

Copas
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clamp
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  • What internalFormat are you using in that texture? – Dr. Snoopy Sep 03 '10 at 16:07
  • Can I get more information on the PNG? Like how was it saved? – Octavian Helm Sep 06 '10 at 11:24
  • it was saved with photoshop, and believe me, it has an alpha channel with varying values. it is not binary transparent. – clamp Sep 06 '10 at 11:28
  • Would you post a link to the PNG file so I can test it with the same resources? Only if possible. – Octavian Helm Sep 06 '10 at 11:54
  • http://deviantsart.com/upload/2757n63.png but again, i dont think the PNG is the problem, because i use PNGs like this a lot in normal GL rendering and they work fine. – clamp Sep 06 '10 at 12:06
  • I didn't state that the PNG is the problem I just wanted to have the same resources to be able to reproduce the result. ;) – Octavian Helm Sep 06 '10 at 12:23
  • @clamp PNG is not an internal format. The internal format is a parameter to the glTexImage2D call. What value are you using for that parameter? – Dr. Snoopy Sep 08 '10 at 16:14

4 Answers4

3

Try this:

gl.glEnable(GL10.GL_BLEND);    
gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);

gl.glEnable(GL10.GL_ALPHA_BITS);
//draw...
gl.glDisable(GL10.GL_ALPHA_BITS);
cement
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1

It seems like it's using alpha testing instead of alpha blending, which would explain the thresholding behaviour. Although it isn't enabled by default, it might be worth to try:

gl.glDisable(GL10.GL_ALPHA_TEST);
Aert
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0

What surface format are you using for your GLSurfaceView? Is it a translucent (not transparent) format?

surfaceView.getHolder().setFormat(PixelFormat.TRANSLUCENT);

Also the EGL settings must have alpha support set. This will give you the best of quality...

surfaceView.setEGLConfigChooser(8, 8, 8, 8, 16, 0);

Edit: Another thought is that perhaps you didn't upload the image to OpenGL in a translucent format with glTexImage2D?

Moncader
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0

Are you storing the PNG to a GL texture that only has 1 bit of alpha, such as 16-bit 5-5-5-1 format? This would cause the behavior above.

Mikko Strandborg
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