Hi,
> >>> I use a TextureGrabForeground to do some multipass
> >>> rendering. I need to access the texture coordinates
> >>> of the valid rect of the texture, depending on extensions
> >>> like GL_ARB_texture_non_power_of_two supported by the
> >>> target machine. Methods like getTexCoords are not exposed
> >>> by the interface... So how do I access the texture
> >>> cords? (Note that the coordinates might change during
> >>> runtime depending on the current size of the viewport
> >>> (resizing, etc))
> >> It is possible to get the pixel-size of the viewport (see
> >> getPixelWidth()/getPixelHeight() in osg::Viewport) so you should be
> able
> >> to use that to compute your actual texcoords.
> >>
> >> Does this help?
> >
> > Yes, I guess that's what I thought I had to do. But I must
> > know how tex coords are calculated inside TextureGrabForeground,
> > so I guess I'll have to take a look at the code.
>
> Ah, you want to figure out how large an image was grabbed and where it
> ends up in your texture?
>
> With image grabbing, there are no tex-coords 'calculated' as such, since
> it only grabs an image and put's it into another image (the texture).
yes
> Looking at TextureGrabForeGround, it copies the viewport (at viewport
> left/bottom and with max width/height of viewport or image) to the
> bottom left of the texture (0,0)).
yepp...
> As texture coords is only associated with polygon corners when
> rendering, and is mapped as GL defines it (for NPOT: 0,0 at bottom left,
> 1,1 upper right w.r.t. the full size of the texture), I would think that
> using (0,0) and (1.0/min(viewport->getPixelWidth(),
> texture->getimage()->getWidth()), 1.0/ditto(height)) would work, but I
> assume you've tried that?
Well yes... my solution right now looks like this:
void calcTextureCoordinates( int width, int height, float &u, float &v )
{
bool isPOT = osgispower2(width) && osgispower2(height);
bool hasNPot = win.hasExtension("GL_ARB_texture_non_power_of_two");
bool hasRectTex = win.hasExtension("GL_ARB_texture_rectangle");
if((isPOT || hasNPot) && !hasRectTex){
u = v = 1.0;
}else if(hasRectTex){
u = width-1;
v = height-1;
}else{
u = static_cast<Real32>(width) / osgnextpower2(width);
v = static_cast<Real32>(height) / osgnextpower2(height);
}
}
then I do something like this:
ViewportPtr vp = ...;
calcTextureCoordinates( vp->getPixelWidth(), vp->getPixelHeight(), u, v );
Seems to work...
Regards and thank you Marcus,
Toni
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