Hi Oliver,
On Thu, 2005-08-18 at 19:27 +0200, Oliver Kutter wrote:
> Hello World ;-) ,
>
> I have a problem with accessing textures in my fragment shader program.
> I want to access the texture, but not at the fragment's current
> position. Normally, the program looks up the texture at the specified
> fragment texture coordinates stored in gl_TexCoords[0]. But I want to
> get texture values from other coordinates.
>
> Example:
>
> Normal you do:
>
> vec4 myFragColor = texture2D (myTexture, vec2 (gl_TexCoords[0]));
> gl_FragColor = myFragColor;
>
> But I want to do:
>
> float texSize = 256.0;
> float x = xpos / texSize;
> float y = ypos / texSize;
> vec4 myFragColor = texture2D (myTexture, vec2 (x, y));
> gl_FragColor = myFragColor;
>
> Now my Problem:
> When I choose xpos and ypos as fixed values (e.g. xpos = 50.0, ypos =
> 100.0), I have no problem. I get exactly the color at the specified
> coordinates (50,100) in the texture.
> But when I choose xpos and ypos to be variable (what I want to achieve),
> I get everytime, when I start my application, different color values.
> The funny thing is, that I have everytime the same (correct) texture
> coordinates. Sometimes I get the correct color values, but mostly I get
> the wrong values.
> I tested it with the following code (I can take x and y as color values):
>
> gl_FragColor = vec4 (myFragColor.x, x, y, 1.0);
>
>
>
> Has anyone an idea?
That sounds reasonable and simple. Have you tried running it on a
different graphics card/driver combo? GLSL is still not as stable as it
should be, even though your example is simple enough that I wouldn't
expect it to be a problem.
Yours
Dirk
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