glUseProgram(glsl_program_num);
check_error();
glUniform1i(glGetUniformLocation(glsl_program_num, "tex"), 0); // Bind the 2D sampler.
glUseProgram(glsl_program_num);
check_error();
glUniform1i(glGetUniformLocation(glsl_program_num, "tex"), 0); // Bind the 2D sampler.