CG->GLSL, FilterManager: texpad_x

Scripting Issues
1

I’m attempting to port a CG shader of mine to GLSL, and have hit a problem: I’m not sure of how to use the “texpad_x” variable in GLSL.

Specifically, I’m using FilterManager to set up some post-processing effects. Naturally, I want to adjust the texture coordinates to account for the (presumed) padding to a power-of-two texture, as indicated in the manual. In CG this is accomplished via the “texpad_x” variable (where “x” is the name of the texture involved, as given via “setShaderInput”), I believe–and indeed, in CG this seems to work. In GLSL, however, it seems that either I’m doing something incorrectly, or the variable doesn’t exist.

Where am I going wrong?

Here is the vertex shader in which I’m using “texpad”:

#version 120

attribute vec4 p3d_Vertex;
attribute vec4 p3d_MultiTexCoord0;

uniform vec4 texpad_colourTex;

void main()
{
    gl_Position = ftransform();
    gl_TexCoord[0] = p3d_MultiTexCoord0*texpad_colourTex + texpad_colourTex;
}

Note “texpad_colourTex” on the sixth line.

The actual texture, “colourTex”, is declared and used in the fragment shader, which does not use (nor declare) “texpad_colourTex”.

1 Like
2

As far as I remember texpad is just “aspect ratio” of texture? How it can help in adjusting? If I understand texture should be itself power-of-two, i.e. it should have U2 x W2 resolution and it’s not related to the texcoords.

3

If you have a 800x600 window and you render that to a buffer with power-o-2 textures on you will get a 1024x1024 texture with a 800x600 image and some empty space. Texpad helps to crop this to only the used pixels. I think you should be able to supply a texpad value from python vec4(win_y/tex_y, win_x/tex_x, 1.0, 1.0)… or x and y the other way, and make sure you get floats not ints on python 2.x

Or You can assume that all gpu support non-power-of-two textures and don’t mess with texpad.

4

Ah, you right, I forget about this feature. I’ve tried to implement it in GLSL, and in my case formula looked like this:
Panad

quad.setShaderInput('texpad_tex', Vec2(screen_w/tex_w*0.5, screen_h/tex_h*0.5))

Shader

uniform vec2 texpad_tex;
.....
gl_TexCoord[0].xy = gl_Position.xy * texpad_tex + texpad_tex;

And you should to update texpad when window is changed

5

Aah, thank you both–that looks about right; I’ll hopefully try it out tomorrow.

It’s a pity that the automatic version doesn’t seem to work in GLSL as it does in CG, but as you’ve pointed out, it’s not too difficult to provide the value oneself.

6

Just FYI, there’s not a lot of merit to the texture padding system nowadays. It’s pretty safe to just set “textures-power-2 none” in Config.prc if you have a shader-based application.

1 Like
7

Really? That should make life easier–thank you! :slight_smile:

8

According to the well-known 0AD study, 96% of users support non-power-of-two textures:
feedback.wildfiregames.com/repor … wer_of_two

9

That’s good to know–thank you again. :slight_smile:

(And it’s a mild relief to see that my own card does indeed seem to be on that list–it’s a little old these days, so I wasn’t entirely confident. ^^; )