pyopengl-users

[PyOpenGL-Users] texture arrays or 3 textures

[Philip W. <pwi...@gm...>]

I have a shader which takes a 16-bit index and looks into a 256x256 table
for an RGBA value, a colormap  I want to extend it to handle larger indexes.
 I think the best way is create a texture array or a 3D texture with
multiple 256x256 textures.  Then instead of looking up just U, V I would
look up R, S, T.

Are texture arrays and 3d textures both supported in PyOpenGL? Is one better
suited to this problem?  I want an exact nearest-neighbor lookup, no
filtering in X, Y or Z.

Thanks.

-Philip

Re: [PyOpenGL-Users] texture arrays or 3 textures

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

On Thu, Jun 3, 2010 at 11:05 AM, Philip Winston <pwi...@gm...> wrote:

> I have a shader which takes a 16-bit index and looks into a 256x256 table
> for an RGBA value, a colormap  I want to extend it to handle larger indexes.
>  I think the best way is create a texture array or a 3D texture with
> multiple 256x256 textures.  Then instead of looking up just U, V I would
> look up R, S, T.
>

> Are texture arrays and 3d textures both supported in PyOpenGL? Is one
> better suited to this problem?
>
3D textures I know are, because I've used them, and texture arrays likely
are too.

What is the context of this problem?  A 3D texture would certainly work, but
these suffer from memory issues, complexity, and
graphics-cards-generally-not-liking-them.  You might do better to "unroll"
the 3D texture into a 2D texture, although again, complexity.

> I want an exact nearest-neighbor lookup, no filtering in X, Y or Z.
>
Use GL_NEAREST when making the texture(s)

> Thanks.
>
> -Philip
>
Ian

Re: [PyOpenGL-Users] texture arrays or 3 textures

[Philip W. <pwi...@gm...>]

On Fri, Jun 4, 2010 at 1:14 PM, Ian Mallett <geo...@gm...> wrote:

> What is the context of this problem?


It's a false-color display on top of grayscale images. We have a grayscale
image and a separate image which contains a per-pixel segment index.  Then
we have a colormap which maps segment indexes to RGBA values.  The shader
looks the color up in the colormap then blends it with the grayscale value.

Initially we used LUMINANCE_16 images, so only 16-bit indexes, and a fixed
256x256 colormap.  We moved to RGB  to hold up to 24-bit indexes because
some images are large and have more than 65k segments.


> A 3D texture would certainly work, but these suffer from memory issues,
> complexity, and graphics-cards-generally-not-liking-them.
>

That's not very encouraging...  so are "texture arrays" even worse?


>  You might do better to "unroll" the 3D texture into a 2D texture, although
> again, complexity.
>

That's what we do now and it is a little complex. The shader needs to know
the shape/size of the texture and do a bit of math to convert from RGB index
to UV.  With a 3D texture it seems we can directly use the RGB index as the
STR coordinates for a 256x256xN texture.  The texture can be only as deep as
is needed, based on the size of the colormap.

So older cards don't like 3D Textures or does it continue to be a problem
even for newer hardware?  We have only two dozen users, mostly newish Quadro
3800 cards.

-Philip

Re: [PyOpenGL-Users] texture arrays or 3 textures

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

On Fri, Jun 4, 2010 at 10:55 AM, Philip Winston <pwi...@gm...> wrote:

> That's not very encouraging...  so are "texture arrays" even worse?
>
Portability is not really such a huge problem.  It's just not given
functionality.  Newer cards probably support it; it's much older cards that
will difficulty, as is evident here:
http://www.opengl.org/resources/code/samples/sig99/advanced99/notes/node390.html.
Although, if you're writing for cards with programmable shaders, then
chances are 3D texturing will be supported in all its glory.

> That's what we do now and it is a little complex.  The shader needs to know
> the shape/size of the texture and do a bit of math to convert from RGB index
> to UV.  With a 3D texture it seems we can directly use the RGB index as the
> STR coordinates for a 256x256xN texture.  The texture can be only as deep as
> is needed, based on the size of the colormap.
>

> So older cards don't like 3D Textures or does it continue to be a problem
> even for newer hardware?  We have only two dozen users, mostly newish Quadro
> 3800 cards.
>
Then you're probably fine.  A 3D texture is great, especially for new cards
and future cards.

> -Philip

Ian