rough pseudo-code:
glGenTextures(1, &scaledTexture); // make the destination scaled texture
// TODO: set up texture dimensions via glTexImage2D
glGenFramebuffers(1, &myFBO); // make the drawing FBO to perform the scaling
glBindFramebuffer(GL_FRAMEBUFFER_EXT, myFBO);
glFramebufferTexture2D(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
GL_TEXTURE_2D, scaledTexture, 0);
glDrawBuffer(GL_COLOR_ATTACHMENT0);
// bind source texture -- you might just use the bindTextureRep call here?
glBindTexture(GL_TEXTURE_2D (or rect?), yourInputTexture);
// set up projection -- pixel-for-pixel orthographic
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0,0,width,0,height, -1, 1);
// draw the source to the destination
// TODO: if better-than-bilinear-scaling is desired, add a shader here to do
bicubic or something
glBegin(GL_QUADS);
glTexCoord2f(0,0);
glVertex2f(0,0);
glTexCoord2f(1,0);
glVertex2f(width,0);
glTexCoord2f(1,1);
glVertex2f(width,height);
glTexCoord2f(0,1);
glVertex(0, height);
glEnd();
// done! scaledTexture now has the scaled contents using bilinear scaling in
hardware
// make sure to delete fbos and texture when done.
// ALSO: RESTORE ALL THE GL STATE! NOT DOING SO WILL BLOW UP!
On Nov 21, 2012, at 7:55 AM, Christophe Leske <i...@multimedial.de> wrote:
> Hi there,
>
> I would like to scale a texture image in the GPU to a new format - I got this
> in place already for my patch - how do I scale the texture and get the pixel
> data from it?
>
> Can anyone point me into the right direction, please?
>
>
> // open gl
> CGLContextObj cgl_ctx = [context CGLContextObj];
> GLenum error;
>
>
> if (![imageToUse lockTextureRepresentationWithColorSpace:colorSpace
> forBounds:[imageToUse imageBounds]])
> {
> NSLog(@"Locking of texture failed.");
> return NO;
> }
>
> [imageToUse bindTextureRepresentationToCGLContext:cgl_ctx
> textureUnit:GL_TEXTURE0 normalizeCoordinates:YES];
>
>
> // scaling in opengl comes here...
> // uuuuuuuuuh....
>
>
> [imageToUse unbindTextureRepresentationFromCGLContext:cgl_ctx
> textureUnit:GL_TEXTURE0];
>
> [imageToUse unlockTextureRepresentation];
>
>
>
>
>
> --
> Christophe Leske
> multimedial.de
>
> ----------------------------------------
> www.multimedial.de - i...@multimedial.de
> Hohler Strasse 17 - 51645 Gummersbach
> +49(0)2261-99824540 // +49(0)177-2497031
> ----------------------------------------
>
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