Re: [PyOpenGL-Users] Tricky question on shader

[Ian M. <geo...@gm...>]

On Wed, Aug 31, 2011 at 3:48 PM, Nicolas Rougier
<Nic...@in...>wrote:

>
> Hi folks,
>
> I've been playing with gaussian texture filtering using shaders and I
> obtained a strange "grid" effect on a completely uniform texture. Since all
> fragments get the same processing and same neighbouring values,I wonder if
> the grid is the result of some kind of artifact with floating points or the
> way texture coordinates are interpolated. Or I missed something completely
> obvious…
>
> I attached the code below. It is self-contained and you should see the grid
> I'm talking about.
>
> Nicolas

It feels like the texture coordinates as you calculate them in
interpolate(...), and the offsets in filter(...) are to blame.  I assume
you're trying to do something like a "manual" minification filter using a
gauss kernel.  Without knowing more about the algorithm, I can't say.

My recommendation is to try gamedev.net in the OpenGL forum, as there are a
large number of people there who can help.

Ian