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Thread: 32 BPP textures

  1. #1

    32 BPP textures


    There is a problem that I can't figure out. I have a properly loaded 32bpp bitmap and to create a mipmap texture that can take advantage of alpha component I should use a following line :

    gluBuild2DMipmaps(GL_TEXTURE_2D, 4, width, height, GL_RGBA, GL_UNSIGNED_BYTE, bitmap);

    Right? OK, but when I draw the texture it appears to lose its color depth (something like 16bpp). Suprisingly, when I specify that I use 3 components the texture colors remain valid but ... of course blending does not work. Something like this :

    gluBuild2DMipmaps(GL_TEXTURE_2D, 3, width, height, GL_RGBA, GL_UNSIGNED_BYTE, bitmap);

    What can be the problem ?? I'd be thankful for any help!


  2. #2
    Super Moderator OpenGL Guru imported_dorbie's Avatar
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    Jul 2000
    Bay Area, CA, USA

    Re: 32 BPP textures

    When you specify 4 as the internal format you may be getting RGBA4444 but with 3 for internal format may get more color precision with RGB565. Instead of specifying 4 as the internal format you could try to be more explicit about texture format precision with some of the other internal format tokens. Try specifying GL_RGBA8 as the internal format token and it should give you a full 32 bits of precision if that is supported by your card. It may reduce your pixel fill performance and will use more texture memory as a result, there are other tokens that may be sufficient for you but still use less texture memory and fill faster, for example GL_RGB5_A1, but that will depend on your specific requirements.

  3. #3

    Re: 32 BPP textures


    One more question if you don't mind ... How do you think - is it better to use GL_RGBA8 textures or to simply use texture & transparency mask? Which one is more efficient ?

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