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[SOLVED] GLSL subroutine not getting used

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#1 d0Sm4o20   Members   


Posted 08 April 2012 - 03:57 PM

I'm using a gaussian blur fragment shader. In it, I thought it would be concise to include 2 subroutines: one for selecting the horizontal texture coordinate offsets, and another for the vertical texture coordinate offsets. This way, I just have one gaussian blur shader to manage.

Here is the code for my shader. The {{NAME}} bits are template placeholders that I substitute in at shader compile time:

	#version 420
	subroutine vec2 sample_coord_type(int i);
	subroutine uniform sample_coord_type sample_coord;
	in vec2 texcoord;
	out vec3 color;
	uniform sampler2D tex;
	uniform int texture_size;
	const float offsets[{{NUM_SAMPLES}}] = float[]({{SAMPLE_OFFSETS}});
	const float weights[{{NUM_SAMPLES}}] = float[]({{SAMPLE_WEIGHTS}});
	subroutine(sample_coord_type) vec2 vertical_coord(int i) {
	 return vec2(0.0, offsets[i] / texture_size);
	subroutine(sample_coord_type) vec2 horizontal_coord(int i) {
	 //return vec2(offsets[i] / texture_size, 0.0);
	 return vec2(0.0, 0.0); // just for testing if this subroutine gets used

	void main(void) {	
		color = vec3(0.0);
		for (int i=0; i<{{NUM_SAMPLES}}; i++) {
			color += texture(tex, texcoord + sample_coord(i)).rgb * weights[i];
			color += texture(tex, texcoord - sample_coord(i)).rgb * weights[i];

Here is my code for selecting the subroutine:

	blur_program->set_subroutine("sample_coord", "vertical_coord", GL_FRAGMENT_SHADER);
	blur_program->set_int("texture_size", width);
	blur_program->set_texture("tex", *deferred_output);
	blur_program->draw(); // draws a quad for the fragment shader to run on


	void ShaderProgram::set_subroutine(constr name, constr routine, GLenum target) {
	 GLuint routine_index = glGetSubroutineIndex(id, target, routine.c_str());
	 GLuint uniform_index = glGetSubroutineUniformLocation(id, target, name.c_str());
	 glUniformSubroutinesuiv(target, 1, &routine_index);
	 // debugging
	 int num_subs;
	 glGetActiveSubroutineUniformiv(id, target, uniform_index, GL_NUM_COMPATIBLE_SUBROUTINES, &num_subs);
	 std::cout << uniform_index << " " << routine_index << " " << num_subs << "\n";

I've checked for errors, and there are none. When I pass in `vertical_coord` as the routine to use, my scene is blurred vertically, as it should be. The `routine_index` variable is also 1 (which is weird, because `vertical_coord` subroutine is the first listed in the shader code...but no matter, maybe the compiler is switching things around)

However, when I pass in `horizontal_coord`, my scene is STILL blurred vertically, even though the value of `routine_index` is 0, suggesting that a different subroutine is being used. Yet the `horizontal_coord` subroutine explicitly does not blur.

What's more is, whichever subroutine comes first in the shader, is the subroutine that the shader uses permanently. Right now, `vertical_coord` comes first, so the shader blurs vertically always. If I put `horizontal_coord` first, the scene is unblurred, as expected, but then I cannot select the `vertical_coord` subroutine! Posted Image

Also, the value of `num_subs` is 2, suggesting that there are 2 subroutines compatible with my `sample_coord` subroutine uniform.

Just to re-iterate, all of my return values are fine, and there are no glGetError() errors happening.

Any ideas?

#2 d0Sm4o20   Members   


Posted 09 April 2012 - 01:38 AM

After a lot of pain, I figured out that I was indirectly calling glUseProgram() twice with my framework. The first time, to set the subroutine, the second time, in the draw() method of my shader program object. Apparently subroutine selection *do not* persist in shader program state, so it was being reset on the second call.

Hopefully this saves someone some time! :)

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