Re: Seamless texture tiling?

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Phil Keslin (philk++at++cthulhu.engr.sgi.com)
Thu, 08 Oct 1998 20:10:35 -0700

It's not clear how you are drawing the textured polygon. You need to
ensure that the support for the resampler does not extend past the
border region. Since you are most likely using linear filtering, one
texels should suffice provided that your texture coordinates don't
extend beyond 1/512 to 510/512 (assuming the identity texture matrix).
You also need to make adjustments to your polygon to account for the
reduced mapping.

- Phil

Scott Herod wrote:
>
> I have large textures that I need to map onto geosets.
> "Large" means bigger than 512 on a side. If I make textures
> larger than 512 on a side, there is a subtle shift of the
> texels going from a glDrawPixel to the textured geoset.
>
> Currently, I am trying to cut the textures up into 512x512
> subtextures and paste them onto geosets sitting edge to edge.
> However, as they move, there is sometimes a seam.
>
> In an attempt to fix this, I am making the subtextures
> overlap by two texels, one for each in order to use these
> as a texture border. It appears that performer still wants
> textures with borders to be power-of-two so 2 texels for the
> border and 510 for the viewable portion. I then use
>
> tex->setRepeat( PFTEX_WRAP_S, PFTEX_CLAMP );
>
> This works fine on O2 but fails miserably on OCTANE as seams
> are visible.
>
> Any hints or suggestions for making this work? More details
> are below.
>
> Scott Herod
> scott++at++evt.com
>
> Details:
>
> Turn large texture into series of square tiles which width
> wise are (1 texel border) + (510 texels image) + (1 texel border). For
> each subtexture, the left side border is the
> last visible texel of the subtexture on the left and the
> right side border is the first visible texel of the subtexture
> to the right. (Top to bottom is the same, edge subtextures
> repeat border and first row of visible texels.)
>
> Then for each subtexture use
>
> pfTexture *tex = new pfTexture;
>
> // rimg_w = rimg_h = 512
> tex->setImage( tex_data, num_comps, rimg_w, rimg_h, 1 );
> tex->setBorderType(PFTEX_BORDER_TEXELS);
>
> tex->setRepeat( PFTEX_WRAP_S, PFTEX_CLAMP );
> tex->setRepeat( PFTEX_WRAP_T, PFTEX_CLAMP );
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-- 
Phil Keslin			Silicon Graphics, Inc.
E-Mail: philk++at++sgi.com		2011 N. Shoreline Blvd. M/S 8U-590
				Mountain View, CA 94043

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