USE_DEPTH_BUFFER = 1 affects alpha of textures!?!

Discussion in 'iOS Programming' started by biosopher, Jan 17, 2009.

  1. biosopher macrumors newbie

    Jan 15, 2009
    In Apple's GLSprite (and probably the TouchFighter code as well), setting USE_DEPTH_BUFFER = 1 affects the alpha of textures such that any transparent pixel becomes black.

    I.e. if all I do is change the single value of USE_DEPTH_BUFFER from 1 to 0, I get the transparency I want. Why the dependency between transparency and USE_DEPTH_BUFFER? What am I missing here?

    Image with USE_DEPTH_BUFFER = 0

    Image with USE_DEPTH_BUFFER = 1

    I don't understand how creating the depth buffer affects whether the image-based textures are transparent or not. Any ideas?

  2. biosopher thread starter macrumors newbie

    Jan 15, 2009
    Should have added for those that don't have the GLSprite code. This is what the USE_DEPTH_BUFFER code enables:

        glGenRenderbuffersOES(1, &depthRenderbuffer);
        glBindRenderbufferOES(GL_RENDERBUFFER_OES, depthRenderbuffer);
        glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT16_OES, backingWidth, backingHeight);
        glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer);
  3. biosopher thread starter macrumors newbie

    Jan 15, 2009
    OK...maybe I was just optimistic that I could have OpenGL handle my depth testing automatically AND get transparencies as well.

    I just read these discussions of depth testing & alpha transparencies that are telling me otherwise...or at least seem to layout a more complex solution than the simple one I'd hoped for:

    Alpha Blending, Part 1
    Alpha Blending, Part 2
    Alpha Blending, Part 3

    Please let me know if anyone knows can direct me to better discussions or tutorials.


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