Puzzels about glteximage2d using gl_luminance - opengl-es

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.

Answer 2

You're using non-extension FBO functions, which were introduced only with OpenGL-3. So unlike FBO extension functions (ending with ARB) those functions are available only with a OpenGL-3 context. In OpenGL-3 the GL_LUMINANCE and GL_ALPHA texture internal formats are deprecated, are not available in core profile. They have been replaced by the GL_RED texture format. You can use an appropriately written shader or texture swizzle parameters to make a GL_RED texture work just like GL_LUMINANCE (swizzle dst.rgb = texture.r) or GL_ALPHA (swizzle dst.a = texture.r).

Answer 3

I have solved by using GL_RG_EXT, or GL_RED_EXT, instead.