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Multiple Render Target shader question.


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#1 hellishdude   Members   -  Reputation: 111

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Posted 04 November 2012 - 06:29 AM

Hello everbody! I'm new to this forum although I've been reading the threads for quite a while now, and I have to say its my top favorite destination when comes to opengl related stuff.

On with my problems(if you can call it that). You see I'm quite new with GLSL and I was following an example for deferred rendering found here:
http://ogldev.atspac...tutorial35.html. The only problem is ( for me) that he is using a library called GLFX to complile shaders. This shader source in the project is both vertex shader and fragment in one file called geometry_pass.glsl:

struct VertexInput
{
	vec3 Position;
	vec2 TexCoord;
	vec3 Normal;
};
interface VertexOutput
{
	vec3 WorldPos;
	vec2 TexCoord;
	vec3 Normal;
};
uniform mat4 MVP;
uniform mat4 WV;
									
shader VSmain(in VertexInput VSin:0, out VertexOutput VSout)
{
	gl_Position = MVP * vec4(VSin.Position, 1.0);
	VSout.TexCoord   = VSin.TexCoord;
	VSout.Normal	 = (WV * vec4(VSin.Normal, 0.0)).xyz;
	VSout.WorldPos   = (WV * vec4(VSin.Position, 1.0)).xyz;
};
struct FSOutput
{
	vec3 WorldPos;
	vec3 Diffuse;
	vec3 Normal;
	vec3 TexCoord;
};
		
uniform sampler2D gColorMap;
		
shader FSmain(in VertexOutput FSin, out FSOutput FSout)
{
		FSout.WorldPos = FSin.WorldPos;
		FSout.Diffuse  = texture(gColorMap, FSin.TexCoord).xyz;
		FSout.Normal   = normalize(FSin.Normal);
		FSout.TexCoord = vec3(FSin.TexCoord, 0.0);
};
program GeometryPass
{
	vs(410)=VSmain();
	fs(410)=FSmain();
};


My problem is that I need to have a vertex shader and fragment shader seperated: For example geometry_pass.vert and geometry_pass.frag.

I think I've fixed the vertex shader(not really sure) it compiles fine.
Geometry_Pass.vert:

#version 150 core
uniform mat4 MVP;
uniform mat4 WV;
in vec3 in_Position;
in vec2 in_TexCoord;
in vec3 in_Normal;
out vec3 WorldPos;
out vec2 pass_TexCoord;
out vec3 pass_Normal;
void main()
{
	gl_Position = MVP * vec4(in_Position,1.0);
	pass_TexCoord = in_TexCoord;
	pass_Normal = (WV * vec4(in_Normal, 0.0)).xyz;
	WorldPos = (WV * vec4(in_Position,1.0)).xyz;
};


When I'm trying to pass the texcoords or normals to fragment I get naming conflicts and such, although I was under the impression that passing an attribute from vertex to fragment shader requires the same name. Can anyone please help me with the spliting of the file into two shaders or explain me what I may be doing wrong? Sorry I'm quite new to glsl and I'm reading thought materials and books and the information is just too overwelming Posted Image.

And something else, is it possible to pass structs(blocks) from vertex to fragment shader?

Thank you very much.

Edited by hellishdude, 04 November 2012 - 12:35 PM.


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#2 max343   Members   -  Reputation: 340

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Posted 04 November 2012 - 10:12 AM

Are the inputs in the fragment shader the same as the outputs in the vertex shader? They must match not only in name, but also in type and qualifiers.

As for your second question, you can declare interface blocks for output/input.
They work pretty much like structs, except you can define qualifiers on the passed variables.

#3 hellishdude   Members   -  Reputation: 111

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Posted 04 November 2012 - 11:48 AM

As for your second question, you can declare interface blocks for output/input.
They work pretty much like structs, except you can define qualifiers on the passed variables.


Well now I'm a bit confused because I've read the glsl specification and it states that in/out block decleration can not pass from the vertex to the fragment shader. They only use it for the geometry shader.

From my understanding it should be something along this lines:

Vertex Shader:
#version 410 core
uniform mat4 MVP;
uniform mat4 WV;
struct VertexInput
{
    vec3 Position;
    vec2 TexCoord;
    vec3 Normal;
};
out VertexOutput
{
    vec3 WorldPos;
    vec2 TexCoord;
    vec3 Normal;
};
void main()
{
    gl_Position = MVP * vec4(VertexInput.Position,1.0);
    VertexOutput.TexCoord = VertexInput.TexCoord;
    VertexOutput.Normal = (WV*vec4(VertexInput.Normal,0,0)).xyz;
    VertexOutput.WorldPos = (WV * vec4(VertexInput.Position)).xyz;
}


Fragment Shader:
#Version 410 core

in VertexOutput
{
    vec3 WorldPos;
    vec3 Diffuse;
    vec3 Normal;
    vec2 TexCoord;
};
struct FSOutput
{
    vec3 WorldPos;
    vec3 Diffuse;
    vec3 Normal;
    vec3 TexCoord;
};
uniform sampler2D gColorMap;
void main (void)
{
    FSOutput.WorldPos = VertexOutput.WorldPos;
    FSOutput.Diffuse = texture2D(gColorMap, VertexOutput.TexCoord).xyz;
    FSOutput.Normal = normalize(VertexOutput.Normal);
    FSOutput.TexCoord = vec3 (VertexOutput.TexCoord, 0.0);
}

what do I do wrong?

#4 max343   Members   -  Reputation: 340

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Posted 04 November 2012 - 05:45 PM

Just reread (to be sure) and haven't seen such statement. Besides, it has always worked for me ;)

In your example your blocks don't match. Basically you need to copy-paste and change "out" to "in" (or vice versa).

#5 hellishdude   Members   -  Reputation: 111

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Posted 05 November 2012 - 04:33 AM

Just reread (to be sure) and haven't seen such statement. Besides, it has always worked for me ;)


http://www.opengl.org/wiki/GLSL_Interface_Block

"Interface blocks can only be used to aggregate data interfaces between shaders. Vertex shaders cannot declare an input interface block, and fragment shaders cannot declare an output interface block.
If the input interface uses a block, then the corresponding output must also be a block that uses the same block name and members (though not necessarily the same instance name)."

yep, if I declare input block in the vertex shader I get a complile error:
OpenGL does not allow Input Blocks in vertex shaders.

Maybe in the end I need to declare each variable with in and out seperate...

#6 hellishdude   Members   -  Reputation: 111

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Posted 05 November 2012 - 06:09 AM

I think I got it.

Vertex Shader:

#version 410 core
uniform mat4 MVP;
uniform mat4 WV;
in vec3 VertexPosition;
in vec2 VertexTexCoord;
in vec3 VertexNormal;
out vec3 WorldPos;
out vec2 TexCoord;
out vec3 Normal;

void main()
{
    gl_Position = MVP * vec4(VertexPosition, 1.0);
    TexCoord = VertexTexCoord;
    Normal = (WV * vec4(VertexNormal,0.0)).xyz;
    WorldPos = (WV * vec4(VertexPosition, 1.0)).xyz;
}


Fragment Shader:

#version 410 core
in vec3 WorldPos;
in vec2 TexCoord;
in vec3 Normal;
out vec3 FragWorldPos;
out vec3 Diffuse;
out vec3 FragmentNormal;
out vec3 FragTexCoord;
uniform sampler2D gColorMap;
void main (void)
{
    FragWorldPos = WorldPos;
    Diffuse = texture2D(gColorMap, TexCoord).xyz;
    FragmentNormal = normalize(Normal);
    FragTexCoord = vec3(TexCoord, 0.0);
}

Although I don't get any output yet (something is going on in the context probably) the shaders compile and link without compile errors.

#7 max343   Members   -  Reputation: 340

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Posted 05 November 2012 - 06:29 AM

The spec says that you cannot input to vs with interface block, and it makes perfect sense because vs reads the data from a buffer created by the api.
Same for fs, it outputs data to a buffer created by the api, hence no interface blocks.
Interface blocks connect only pipeline stages, with the only exception which is transform feedback (but the connection in this case is implicit).

Now that you matched all outputs to inputs it works. You could've also split the interface block into two blocks, and accomplish the same result.
Generally, using interface blocks is slightly better than just dumping all the variables into the global block, since it gives more structure to your code, but this is really your own choice.

Edited by max343, 05 November 2012 - 06:31 AM.


#8 hellishdude   Members   -  Reputation: 111

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Posted 05 November 2012 - 06:44 AM

Max that makes sense! Thank you very much for sticking with me m8. Really appriciate the explanation.




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