map<GLuint, FBO>::const_iterator format_it = fbo_formats.find(fbo_num);
assert(format_it != fbo_formats.end());
if (format_it->second.texture_num == free_texture_num) {
map<GLuint, FBO>::const_iterator format_it = fbo_formats.find(fbo_num);
assert(format_it != fbo_formats.end());
if (format_it->second.texture_num == free_texture_num) {