Puzzels about glteximage2d using gl_luminance

Question

I met some problem about using gl_luminance to define FBO. Here is the code i used,

 generateRenderToTexture(GL_RGBA, GL_RGBA, GL_UNSIGNED_BYTE, _maskTexture, _imageWidth, _imageHeight, false);

related code is as follows,

TextureBuffer _maskTexture;

class TextureBuffer {
public:
GLuint texture;
GLuint frameBuffer;
GLenum internalformat;
GLenum format;
GLenum type;
int    w,h;

TextureBuffer() : texture(0), frameBuffer(0) {}
void release() 
{
    if(texture)
    {
        glDeleteTextures(1, &texture);
        texture = 0;
    }
    if(frameBuffer)
    {
        glDeleteFramebuffers(1, &frameBuffer);
        frameBuffer = 0;
    }

}
};

void generateRenderToTexture(GLint internalformat, GLenum format, GLenum type,
                                     TextureBuffer &tb, int w, int h, bool linearInterp)
{
    glGenTextures(1, &tb.texture);
    glBindTexture(GL_TEXTURE_2D, tb.texture);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, linearInterp ? GL_LINEAR : GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, linearInterp ? GL_LINEAR : GL_NEAREST);
    glTexImage2D(GL_TEXTURE_2D, 0, internalformat, w, h, 0, format, type, NULL);

    glGenFramebuffers(1, &tb.frameBuffer);
    glBindFramebuffer(GL_FRAMEBUFFER, tb.frameBuffer);
    glClear(_glClearBits);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tb.texture, 0);

    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
    if(status != GL_FRAMEBUFFER_COMPLETE)
        printf("Framebuffer status: %x", (int)status);

    tb.internalformat = internalformat;
    tb.format = format;
    tb.type = type;
    tb.w = w;
    tb.h = h;
}

The question is when I use,

generateRenderToTexture(GL_RGBA, GL_RGBA, GL_UNSIGNED_BYTE, _maskTexture, _imageWidth, _imageHeight, false);

The code went well. But if use gl_luminance instead,

generateRenderToTexture(GL_LUMINANCE, GL_LUMINANCE, GL_UNSIGNED_BYTE,  _maskTexture,  _imageWidthOriginal, 

I don't know why i could not use GL_LUMINANCE to define the FBO. Anyone have some useful suggestions to solve this?

Answer 1

The only formats that are guaranteed to work as color FBO attachments in ES 2.0 are, according to table 4.5 in the spec document:

• GL_RGBA4
• GL_RGB5_A1
• GL_RGB565

Support for rendering to GL_RGBA, which works for you, is not required by the standard. Many implementations support it, though. The OES_rgb8_rgba8 extension adds support for GL_RGB8 and GL_RGBA8 formats as render targets.

GL_LUMINANCE is not supported as a color-renderable format by the standard, and I can't find an extension for it either. It's possible that some implementations could support it, but you certainly can't count on it.

ES 3.0 lists GL_R8 as a color-renderable format. In ES 3.0, the RED/R formats replace the LUMINANCE/ALPHA formats from ES 2.0. So if you can move to ES 3.0, you have support to render to 1-component texture formats.