Precision of glReadPixels when reading unsigned int - opengl

Question

I am having problems storing and retrieving 32 bit unsigned from my framebuffer. The max value for a framebuffer on my intel laptop (nvidia card and Ubuntu) is:
4.294.967.295
However, the max value that i can read, for some reason, is only:
1.040.992.698
I was wondering if someone can tell me if I am doing something wrong or if this a limitation of my graphics card.
I am setting up my framebuffer like this:
// generate render and frame buffer objects
glGenRenderbuffers( 1, &colorbufId );
glGenRenderbuffers( 1, &depthbufId );
glGenFramebuffers ( 1, &framebufId );
// setup renderbuffer
glBindRenderbuffer(GL_RENDERBUFFER, colorbufId);
glRenderbufferStorage(GL_RENDERBUFFER, GL_R32UI, _viewWidth, _viewHeight);
// setup depth buffer
glBindRenderbuffer(GL_RENDERBUFFER, depthbufId);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT32, _viewWidth, _viewHeight);
// setup framebuffer
glBindFramebuffer( GL_FRAMEBUFFER, framebufId );
glFramebufferRenderbuffer( GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorbufId );
glFramebufferRenderbuffer( GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthbufId );
// check if everything went well
GLenum stat = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if(stat != GL_FRAMEBUFFER_COMPLETE) { printf("stat=%d != %d\n", stat, GL_FRAMEBUFFER_COMPLETE); Error(); exit(0); }
// define where the framebuffer outputs will be written
const GLenum bufs[] = { GL_NONE, GL_COLOR_ATTACHMENT0 };
glDrawBuffers(2, bufs);
Now when i try to read a pixel
const uint32_t MAX_UINT = std::numeric_limits< uint32_t >::max();
glClearBufferuiv(GL_RENDERBUFFER, colorbufId, &MAX_UINT);
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT );
uint32_t pix_value=0;
glReadPixels(0, 0, 1, 1, GL_RED_INTEGER, GL_UNSIGNED_INT, &pix_value);
the value of pix_value = 1.040.992.698.
I have also tried use 'GL_RED' instead of 'GL_RED_INTEGER' but that still does not work.
(for anyone interested, the reason i'm trying to do the above is for picking objects)
EDIT: So in the end this had nothing to do with precision. I was not clearing the buffer correctly. Se answer below

Answer 1

Ok i found the error:
This is the correct command to clear the buffer:
glClearBufferuiv(GL_COLOR, colorbufId, &UNDEF_IDX);
glClear( /*GL_COLOR_BUFFER_BIT |*/ GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT );