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openglfbo

How to retrieve number of attachments to FBO

How can I get number of color attachments to currently bind FBO? I checked glGetInteger and glGetFramebufferAttachmentParameteriv but they don't have enum to get these values.

Solution

  • Untested, but this should do it:

    GLint maxAtt = 0;
glGetIntegerv(GL_MAX_COLOR_ATTACHMENTS, &maxAtt);
int nAtt = 0;
for (int iAtt = 0; iAtt < maxAtt; ++iAtt) {
    GLint objType = GL_NONE;
    glGetFramebufferAttachmentParameteriv(
        GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + iAtt,
        GL_FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE, &objType);
    if (objType != GL_NONE) {
        ++nAtt;
    }
}
// nAtt is the number of color attachments.

    You could do something similar using GL_FRAMEBUFFER_ATTACHMENT_OBJECT_NAME instead of GL_FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE, and comparing the value to 0.