Deffered Shading

OpenGL
1

Hi
I am suppose to implement a shader in GLSL using deferred shading.

As I understand I can write to the textures like this.

gl_FragData[0] = gl_Color;
gl_FragData[1] = vec4(vNormal, pixelDepth);
gl_FragData[2] = vec4(worldPosition, 1.0);
gl_FragData[3] = vec4(diff_coeff, phong_coeff, two_sided, 1.0);

What I don’t understand is how to use the textures in the final rendering. Should this be done in fragment shader?
How is this suppose to work?

Best regards

2

The code uses MRT for baking camera space data into 4 textures.

In the light application stage you unproject the pixel into the world space, compute lighting based on position,normal & coefficients (sampling from the textures you have) and contribute to the pixel color. This, of course is done in a fragment shader.

3

I am not asking you to write the shader but i would be very helpful if you could demonstrate what you mean.

How can I access the textures the in fragment shader? Could you show me how to access texture 1(of 4) in my fragment shader.

Thanks for your help.

4

I don’t get it, isato. Why are you asking about Deferred Shading in GLSL here if you don’t know the basics: sampling from the texture? Draw a full-screen textured quad first, at least.


#version 130

uniform sampler2D unit_normal;

void main(){
 vec2 tc = gl_FragCoord.xy;
 vec4 normal = texture(unit_normal,tc);
}
5

The reason I am asking is that its an assignment. I am a student.

Thanks for your code I think I understand the shading code. The uniforms are variables accessible from both shaders and given bye the main program.

I guess I am asking for the basics then. I have been trying to understand. I recently read

http://www.gamedev.net/reference/programming/features/fbo2/page6.asp

Look at this example

#version 110

void main()
{
	gl_FragData[0] = vec4(0.0, 1.0, 0.0);
	gl_FragData[1] = vec4(0.0, 0.0, 1.0);
}

There is no uniforms declared. How do I know witch textures is on witch index.

uniform sampler2D unit_normal;// I guess this is gl_FragData[1]? 

gl_FragData[0] = gl_Color;
gl_FragData[1] = vec4(vNormal, pixelDepth);
gl_FragData[2] = vec4(worldPosition, 1.0);
gl_FragData[3] = vec4(diff_coeff, phong_coeff, two_sided, 1.0)

;

6

The baking of the G-buffer and its application are two different stages.

For the baking, you attach destination textures to FBO & draw to them at once (MRT) like in the code provided.

For the application, you are just using this 4 textures.
Don’t ask the basics here, read about them on OpenGL wiki.

For shader reference I can point you here:
http://code.google.com/p/kri/source/browse/#hg/engine/shader/g

7

Thanks!

8

Is deferred shading the same as deferred lightning?

I am asking because when googling deferred lightning first hit is wiki deferred shading.

9

No, I believe Deferred Lighting is also referred to as Light Pre-pass. Google it, possibly in combination with Wolfgang Engel. Some good stuff on it in SIGGRAPH 2009 IIRC and also on his blog.

Deferred Shading: store material attributes on framebuffer, and then come back with shader lights and light them.

Deferred Lighting: store light attributes on the framebuffer, and then come back with shader materials and light them.

10

I am trying here to build my G-Buffer. This is an example i found but i don’t understand the color is stored in gl_FragData[2]. This example does not work without a texture on each geometry?

varying vec3 position, normal;

void main(void)
{
	position = vec3(gl_ModelViewMatrix * gl_Vertex);
	normal = gl_NormalMatrix * gl_Normal;
	gl_Position = ftransform();
	gl_TexCoord[0] = gl_MultiTexCoord0;
}

#extension GL_ARB_draw_buffers : enable

varying vec3 position, normal;
uniform sampler2D Tex0;

void main(void)
{
	gl_FragData[0] = vec4(position.xyz, 0.0);
	gl_FragData[1] = vec4(normalize(normal.xyz), 0.0);
	gl_FragData[2] = texture2D(Tex0, gl_TexCoord[0].st);
}
11

Not sure I understand your question. If you don’t have a textures, stuff black, white, or whatever makes sense given your lighting equation in there.

12

I was thinking if my geometry was colored using for glColor.
Pretend that I have a red quad without any texture, just colored with glColor. That will not go in this G-buffer?

13

IIRC, you usually store your material albedo(s) per texel in the G-buffer. Whether it comes from the vertex color, 1 or more textures, or both, makes no difference to the technique. It’s all in how you write the shader and populate the gl_FragData[i] outputs.

14

This topic was automatically closed 183 days after the last reply. New replies are no longer allowed.