Polygon to shader

[Ockonal]

Good news:

uniform sampler2D texture;

void main()
{
    /*vec4 color = texture2D(texture, gl_TexCoord[0].xy);
    color.r = 1.0;
    color.a = 0.0;
    gl_FragColor = color;*/

    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}

Makes it fully red. So the texture is fine, something is wrong with processing it in shader.

[Laurent]

But wait... what you draw (the texture of the polygon) is what's already drawn behind (the grey grid), right?

So the result is ok: you get a red version of what's behind the polygon. If you want full red, don't use the source texture, just output a constant red color like you do in your last post.

[Ockonal]

Making it red is just a test that everything is okay with the texture. As I understand, the texture shold become blue when I write: color.b = 0.9 isn't it? And the texture isn't rendered with more blue color.
---
Oh, it seems that I misunderstand something

[Laurent]

color.b = 0.9 just changes the blue component of the pixel to 0.9, but the other components stay the same, i.e. you still get the inital pixel from the source texture; it's just more or less blue now.

So we can consider that you test was successful: it shows that the texture is correctly mapped on the polygon (there's no offset with the background) and that your simple shader works, and can now be improved.

[Laurent]

However...

the texture isn't rendered with more blue color

Is the texture really drawn unchanged? You should see a difference, it should be either more blue or more yellow. Unless 0.9 is the exact value of the blue component of every pixel in the source texture.

[Ockonal]

You were right, thanks! The theme is closed now.