Shaders and texture rects

[Synyster_Coder]

Hey guys,

So I have this problem:

I have a texture that is let's say 1024x1024.
I have a sprite with a subrect of 100,200,500x500.
I have a wave fragment shader that is this:

uniform sampler2D texture;                       //sf::Shader::CurrentTexture
uniform vec3 iResolution;                          //1000,800,1
uniform float time;                                    //A Clock returning miliseconds
uniform float waveWidth;                         //50
uniform float amplitude;                           //150
uniform float speed;                                //100
void main()
{
   vec2 colour = gl_FragCoord.xy / iResolution.xy;

   colour.y = 1.0 - colour.y;

   colour.y += sin(colour.x*waveWidth+(time/speed))/amplitude;

   gl_FragColor = texture2D(texture,colour);
}

The problem is that the whole texture not just the subrect is being scaled to the size of the window and having the wave effect.

I have tried adding this code:

glViewport(100,200,500,500);

But this didn't work.

Anyone have any ideas of how I could maintain the subrect of the sprite?

Thanks everyone!

[Laurent]

Since you use the fragment position rather than texture coordinates (or anything else correlated to the sprite's subrect) for texture lookup, the results are not very surprising.

[Synyster_Coder]

Thank's for the help, so you are saying if I were to use gl_TexCoord[0] instead I would have better results?

[Synyster_Coder]

That worked perfectly thank you very much!!

Just so everyone can see this is the new shader:

uniform sampler2D texture;
uniform float time;
uniform float waveWidth;
uniform float amplitude;
uniform float speed;
void main()
{
   vec2 colour = gl_TexCoord[0].xy;

   colour.y += sin(colour.x*waveWidth+(time/speed))/amplitude;

   gl_FragColor = texture2D(texture,colour);
}

[Laurent]

The variable name "colour" is misleading, since this is a set of coordinates, not a color. The actual color is obtained after looking up the texture at the specified coordinates

[Synyster_Coder]

How right you are, thanks!