Couple GLSL questions

OpenGL
1

I was trying regular blending to composite 3 or 4 textures along with the polygon color. It’s ended up rather tricky and someone mentioned I should look into doing it with a pixel shader instead. I was following this tutorial. http://www.lighthouse3d.com/opengl/glsl/index.php?oglexample1

I can get it to compile with no errors but nothing shows up. So I had a few questions to make sure I was doing things right. First of all is that all the code necessary for a program to use a shader. Second can you have a fragment shader without a vertex shader? Third what do the lines…

const char * vv = vs;
const char * ff = fs;

do? Well not what they do, I know that, but how important are they? Because I’m using c# and not c++ and it doesn’t like the fact that those lines are stuck in the middle. Oh and I am right in thinking that this will paint every fragment red right?

void main(void)
{
gl_FragColor = vec4 (1.0,0.0,0.0, 1.0);
}

I know these are newbie questions, but you got to learn somehow.

2

Originally posted by Lehm:
[b]I was trying regular blending to composite 3 or 4 textures along with the polygon color. It’s ended up rather tricky and someone mentioned I should look into doing it with a pixel shader instead. I was following this tutorial. http://www.lighthouse3d.com/opengl/glsl/index.php?oglexample1

I can get it to compile with no errors but nothing shows up. So I had a few questions to make sure I was doing things right. First of all is that all the code necessary for a program to use a shader. Second can you have a fragment shader without a vertex shader? Third what do the lines…

const char * vv = vs;
const char * ff = fs;

do? Well not what they do, I know that, but how important are they? Because I’m using c# and not c++ and it doesn’t like the fact that those lines are stuck in the middle. Oh and I am right in thinking that this will paint every fragment red right?

void main(void)
{
gl_FragColor = vec4 (1.0,0.0,0.0, 1.0);
}

I know these are newbie questions, but you got to learn somehow.[/b]

  1. yes, if you want to use GLSL you have to do almost all the things included in the code

  2. yes you can use only vertex or fragment shader. However I have heard that there are some problems with it on ATIs ( I’m not sure if the problems are still there or not … )

  3. I think they are there only to cast char* to const char* …nothing important

  4. Yes it should paint all fragments red. ( but you have to select right position of fragments in vertex shader ( ie. gl_Position=ftransform(); }

3

Originally posted by Trahern:

  1. Yes it should paint all fragments red. ( but you have to select right position of fragments in vertex shader ( ie. gl_Position=ftransform(); }[/QB]
    So what your saying is that I have to use a vertex shader to specify gl_FragColor? If so it’s possible to write a VS that just uses the built in transforms right?
4

Originally posted by Lehm:
[b] [quote]Originally posted by Trahern:

  1. Yes it should paint all fragments red. ( but you have to select right position of fragments in vertex shader ( ie. gl_Position=ftransform(); }[/b]
    So what your saying is that I have to use a vertex shader to specify gl_FragColor? If so it’s possible to write a VS that just uses the built in transforms right?[/QB][/QUOTE]no you dont have to use a vertex shader to specify gl_FragColor. You just have to specify position of a vertex in vertex shader ( and of course only if you are using a VS … if not then the standard openGL vertex shader should specify the position for you ( but to be honest I have never tried this …I always use both vertex and fragment shader ))
5

Well okay. I decided to add a vertex shader that simply does…

void main()
{
gl_Position = ftransform();
}

But I still get nothing. I’e followed the tutorial as closely as I could. The only difference being those const lines. I get no errors and everything seems to be loading properly. Any ideas on where to start debugging? I don’t know enough to know why it simply wouldn’t show up.

6

download someone elses code that does the same thing + see why that works and why youres doesnt, step through with a debugger and see where they differ

7

Finally figured it out. It was being enabled, but if you changed screen resolutions it was disabled. So the solution was just to reload the shaders everytime the resolution changed.

8

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