opengl - Precision of glReadPixels when reading unsigned int -

i having problems storing , retrieving 32 bit unsigned framebuffer. max value framebuffer on intel laptop (nvidia card , ubuntu) is:

4.294.967.295

however, max value can read, reason, only:

1.040.992.698

i wondering if can tell me if doing wrong or if limitation of graphics card.

i setting framebuffer this:

  // generate render , 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 went   glenum stat = glcheckframebufferstatus(gl_framebuffer);     if(stat != gl_framebuffer_complete) { printf("stat=%d != %d\n", stat, gl_framebuffer_complete); error(); exit(0); }    // define framebuffer outputs written   const glenum bufs[] = { gl_none, gl_color_attachment0 };   gldrawbuffers(2, bufs); 

now when try read 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 tried use 'gl_red' instead of 'gl_red_integer' still not work.

(for interested, reason i'm trying above picking objects)

edit: in end had nothing precision. not clearing buffer correctly. se answer below

ok found error:

this correct command clear buffer:

  glclearbufferuiv(gl_color, colorbufid, &undef_idx);   glclear( /*gl_color_buffer_bit |*/ gl_depth_buffer_bit | gl_stencil_buffer_bit );