My implementation skips + and - signs

OpenGL
1

Hi All,

Just after putting my shader at work I discovered that my fragment shader doesn’t evaluate the + and - signs while it correctly evaluates the * and / signs.

So if I use

pos.x = pos.x + 10

pos.x is unaffected, while

pos.x = pos.x / 2

pos.x is affected.

I define the shader source as string in C# and after reading the following article I start to be concerned about the source code string encoding.

http://blog.pixelingene.com/?p=224

What do you think?

Thanks,

Alberto

2

try to output the string in a file, to see if it is well encoded.

And I suggest you to use the .0 suffix when affecting a scalar value to a scalar type. There is not implicit type casting.

3

Is there no way to read back the program source from a copiled shader? I think this would be the best test I can do…

Thanks,

Alberto

4

The string you compile is the the one you give to the compiler, so you need to be sure that tihs string is well fitted.

5

Looking to the string in visual studio, the string is fine.

Do you think that if I write it to a txt file I see something different?

Thanks,

Alberto

6

Yes this is what I suggested to you, but I don’t know if it would be different.
I don’t understand why the compiler would skip operator +, there must be a syntax error somewhere else and this would be more visible in a text file.

Just a question, why do you code a shader in a string in the middle of C# code? This is awkward I think.

7

If you have Nvidia card you can use the NVemulate tool (maybe the GLExpert can do that too, I am currently not sure) to force the driver to write both source (as the driver sees it) and compiled shader + compilation logs into files put into application directory.

8

dletozeun,

This is a very easy and short shader, I thought it could be stored within the code.

Am I the first that declare the source code as a string instead or reading it from a txt file?

Thanks,

Alberto

9

Komat,

Unfortunately we are all using ATI graphics cards…

Thanks,

Alberto

10

Use http://glintercept.nutty.org/ to do a XML frame grab and look at the shader source?

11

Very nice tool thanks.

It says what you see below. By the way if I uncomment the commented line I see the texture altered while the line “pos.x = pos.x + 20.0;” don’t affect my texture. Does another reason exist? It is a problem to query a .st value out of the texture size?


//== PROGRAM LINK STATUS = TRUE
//== PROGRAM VALIDATE STATUS = TRUE
/*== INFO LOG ==
Fragment shader(s) linked, no vertex shader(s) defined.d  == INFO LOG END ==*/

//======================================================
//   Fragment Shader 1
//======================================================

//== SHADER COMPILE STATUS = TRUE
/*== INFO LOG ==
Fragment shader was successfully compiled to run on hardware.  == INFO LOG END ==*/

            
// maximum size supported by this shader
const int MaxKernelSize = 49; 

// size of kernel (width * height) for this execution
//uniform int KernelSize;
const int KernelSize = 49; 
  
// array of offsets for accessing the base image
uniform vec2 Offset[MaxKernelSize];

// value for each location in the convolution kernel
uniform vec4 KernelValue[MaxKernelSize];

// image to be convolved
uniform sampler2D BaseImage;

void main()
{

    int i = 0;
    vec4 sum = vec4(0.0);

    for (i = 0; i < KernelSize; i++) 
    {
        vec4 tmp = texture2D(BaseImage, gl_TexCoord[0].st + Offset[i]);
        sum += tmp * KernelValue[i];
    }

  
    vec2 pos = gl_TexCoord[0].st; 

    pos.x = pos.x + 20.0;
//  pos.x = pos.x / 2;

    gl_FragColor = texture2D(BaseImage, pos);
   

}
12

what texture wrap parameters do you use?

13

Default ones. We don’t change them.

14

default texture wrap mode is GL_REPEAT for all texture cordinates. So the integer part of each coordinate is ignored.
That explains why adding a big round value like 20 doesn’t change anything.

15

So these are float coordinates from 0 to 1 ?

I was always thinking about pixel coords.

Thanks so much,

Alberto

16

Just to confirm, texture coordinates are from 0…1 (unless you are using a rectangle texture)

17

Yes, in repeat mode texture coordinates are actually considered in [0, 1] interval and independant of texture size.

18

Thanks guys, my shader is now alive.

sqrt, go on developing and supporting that nice tool!

Alberto

19

Yes sqrt[-1], good precision! :slight_smile: I forgot this one.

20

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