Changing color using a shader

Graphics and GPU Programming Programming

Started by maluh13 February 24, 2011 05:02 AM

9 comments, last by maluh13 13 years, 2 months ago

100

Author

February 24, 2011 05:02 AM

Hello

I am writing a deferred shader and as one of the first steps, to get familiar with GLSL and using shaders and the framebuffer I am trying to change the color of a mesh through a shader.
I have it linked to one of the buffers by calling glDrawBuffers with an array that holds the attachement and then binding the texture to my framebuffer:





	glReadBuffer(GL_NONE);

	GLint color_loc = glGetFragDataLocation(pass_prog,"out_Color");

    	GLenum draws [1];

	draws[color_loc] = GL_COLOR_ATTACHMENT0;

	glDrawBuffers(1, draws);



	glBindTexture(GL_TEXTURE_2D, diffuseTexture);    

	glFramebufferTexture(GL_FRAMEBUFFER, draws[color_loc], diffuseTexture, 0);

i have an out_Color variable in my fragment shader (otherwise it wouldn't even compile), but I can't manage to change the color of the mesh by setting it through that variable inside the shader.
Does anyone has any idea why and could explain that to me?

Thanks

karwosts

841

February 24, 2011 05:51 AM

Please give more information on what else you're doing. What do you mean 'change the color' of the mesh? What color is it now? What does your shader look like? What result do you get?

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maluh13

100

Author

February 24, 2011 05:56 AM

Please give more information on what else you're doing. What do you mean 'change the color' of the mesh? What color is it now? What does your shader look like? What result do you get?

Vertex Shader:





#version 330





uniform mat4x4 u_Model;

uniform mat4x4 u_View;

uniform mat4x4 u_Persp;

uniform mat4x4 u_InvTrans;



in  vec3 Position;

in  vec3 Normal;



out vec3 fs_Normal;

out vec4 fs_Position;

//out vec4 fs_Color;



void main(void) {

	fs_Normal = (u_InvTrans*vec4(Normal,0.0f)).xyz;

	vec4 world = u_Model * vec4(Position, 1.0);

    vec4 camera = u_View * world;

	fs_Position = camera;

	gl_Position = u_Persp * camera;

	//fs_Color = vec4(1.0f, 0.0f, 0.0f, 1.0f);

}

Fragment shader:





#version 330



uniform float u_Far;



in vec3 fs_Normal;

in vec4 fs_Position;



out vec4 out_Normal;

out vec4 out_Position;

out vec4 out_Color;



void main(void)

{

  	out_Normal = vec4(normalize(fs_Normal),0.0f);

	out_Position = vec4(fs_Position.xyz,1.0f); //Tuck position into 0 1 range

	out_Color = vec4(1.0f, 0.0f, 0.0f, 0.5f);//first three diffuse, last specular

}

The shaders do a few other things to get the depth, normal and position textures, which are working.

By change the color I mean sort of like set a diffuse color to the mesh. The mesh is now gray and I am trying to make it look red, or blue, or something.

The result is the mesh being gray.

dpadam450

2,403

February 24, 2011 06:47 AM

If your shader is outputting a static red as shown above, then you probably not compiling and checking errors from the compiler correct. Instead of setting color, set the position of the vertices to be statically (0,0,0) so that no mesh is drawn, see if the mesh still draws(it shouldnt).

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karwosts

841

February 24, 2011 06:51 AM

You need to post your whole of opengl related to your framebuffer, otherwise it's hard to help you. I don't even know if you have created a framebuffer or not.

Have you checked for opengl errors? Framebuffer completeness?

Also you shouldn't bind your texture to a sampler and as a rendertarget at the same time, I believe it's undefined behaviour.

Edit: Changed 'should' to 'shouldn't' (bad typo!).

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maluh13

100

Author

February 24, 2011 06:53 AM

If your shader is outputting a static red as shown above, then you probably not compiling and checking errors from the compiler correct. Instead of setting color, set the position of the vertices to be statically (0,0,0) so that no mesh is drawn, see if the mesh still draws(it shouldnt).

Ok, I changed gl_Position to (0,0,0) in the vertex shader and it doesn't draw it. But in the fragment shader it does nothing. I thought one couldn't change the position in the fragment shader...

maluh13

100

Author

February 24, 2011 07:08 AM

You need to post your whole of opengl related to your framebuffer, otherwise it's hard to help you. I don't even know if you have created a framebuffer or not.

Have you checked for opengl errors? Framebuffer completeness?

Also you should bind your texture to a sampler and as a rendertarget at the same time, I believe it's undefined behaviour.

The frame buffer is created, and I have checked for completeness and openGL errors. And as I said, the normal, depth and position buffers are working.







 	glActiveTexture(GL_TEXTURE0);



	glGenTextures(1, &depthTexture);

    glGenTextures(1, &normalTexture);

	glGenTextures(1, &positionTexture);



	//DEPTH TEXTURE

	glBindTexture(GL_TEXTURE_2D, depthTexture);

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);

	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

	glTexParameteri(GL_TEXTURE_2D, GL_DEPTH_TEXTURE_MODE, GL_INTENSITY);

	glTexImage2D( GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, w, h, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);



	//NORMAL TEXTURE

	glBindTexture(GL_TEXTURE_2D, normalTexture);	

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);	

	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);

	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);		

	glTexImage2D( GL_TEXTURE_2D, 0, GL_RGB32F , w, h, 0, GL_RGBA, GL_FLOAT,0);



	//POSITION TEXTURE

	glBindTexture(GL_TEXTURE_2D, positionTexture);	

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);	

	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);

	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);		

	glTexImage2D( GL_TEXTURE_2D, 0, GL_RGB32F , w, h, 0, GL_RGBA, GL_FLOAT,0);



	//DIFFUSE TEXTURE

	glBindTexture(GL_TEXTURE_2D, diffuseTexture);	

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);	

	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);

	glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);		

	glTexImage2D( GL_TEXTURE_2D, 0, GL_RGB32F , w, h, 0, GL_RGBA, GL_FLOAT,0);



	// create a framebuffer object

	glGenFramebuffers(1, &FBO);

	glBindFramebuffer(GL_FRAMEBUFFER, FBO);



	// Instruct openGL that we won't bind a color texture with the currently binded FBO

	glReadBuffer(GL_NONE);

    GLint normal_loc = glGetFragDataLocation(pass_prog,"out_Normal");

    GLint position_loc = glGetFragDataLocation(pass_prog,"out_Position");

	GLint color_loc = glGetFragDataLocation(pass_prog,"out_Color");

    GLenum draws [3];

    draws[normal_loc] = GL_COLOR_ATTACHMENT0;

    draws[position_loc] = GL_COLOR_ATTACHMENT1;

	draws[color_loc] = GL_COLOR_ATTACHMENT2;

	glDrawBuffers(3, draws);



	glBindTexture(GL_TEXTURE_2D, depthTexture); 

	glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, depthTexture, 0);

	glBindTexture(GL_TEXTURE_2D, normalTexture);    

	glFramebufferTexture(GL_FRAMEBUFFER, draws[normal_loc], normalTexture, 0);

	glBindTexture(GL_TEXTURE_2D, positionTexture);    

	glFramebufferTexture(GL_FRAMEBUFFER, draws[position_loc], positionTexture, 0);

	glBindTexture(GL_TEXTURE_2D, diffuseTexture);    

	glFramebufferTexture(GL_FRAMEBUFFER, draws[color_loc], diffuseTexture, 0);





	// check FBO status

	FBOstatus = glCheckFramebufferStatus(GL_FRAMEBUFFER);

	if(FBOstatus != GL_FRAMEBUFFER_COMPLETE) {

		printf("GL_FRAMEBUFFER_COMPLETE failed, CANNOT use FBO\n");

        checkFramebufferStatus(FBOstatus);

	}





	// switch back to window-system-provided framebuffer

	glClear(GL_DEPTH_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

	glBindFramebuffer(GL_FRAMEBUFFER, 0);

	glBindTexture(GL_TEXTURE_2D, 0);

}

I am not sure what you call a sampler, but I think the diffuseTexture would be the render target, right?

karwosts

841

February 24, 2011 07:16 AM

For the sampler I meant the glBindTexture, you don't need to bind diffuseTexture to GL_TEXTURE_2D to use it as a framebuffer texture. Seems you unbind it before you render though, so I guess that's ok.

If it was still bound to glBindTexture at the same time you were rendering to it I think it would fail. But that doesn't seem like your problem.

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maluh13

100

Author

February 24, 2011 07:22 AM

For the sampler I meant the glBindTexture, you don't need to bind diffuseTexture to GL_TEXTURE_2D to use it as a framebuffer texture. Seems you unbind it before you render though, so I guess that's ok.

If it was still bound to glBindTexture at the same time you were rendering to it I think it would fail. But that doesn't seem like your problem.

Ok. One option discarded. Cool.

But, it is possible, right? To set the color in a shader.
I've heard one can do the diffuse color modulated by the ambient factor in the fixed function pipeline although I am not sure how exactly. But I feel it should also be done in the shader.

karwosts

841

February 24, 2011 07:24 AM

Yeah anything should be possible, but I still don't really get your whole flow. You're drawing a mesh into a framebuffer, what do you do with it then? Do you draw the framebuffer as a fullscreen quad? You haven't put up any drawing code.

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