Re: Convolutions in real time

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Laurent Ach (ach++at++syseca.fr)
Mon, 6 Jul 1998 14:20:54 -0600

On Jul 3, 5:28pm, Miguel Lozano Ibanyez wrote:
> Subject: Convolutions in real time
> Hi,
>
> I'm traying to convolve in real time with Performer 2.1. in a IR.
> After some "panics" in my machine and a lot of 'invalid operation'
> I'd like to know if somebody has done this before.
>
> Now I'm using the accumulation buffer to run convolutions and I
> don't know if this is the best way (better than
> glConvolutionFilter2DEXT?)
>
>-- End of excerpt from Miguel Lozano Ibanyez

I have already filter an image from the framebuffer using
glConvolutionFilter2DEXT on an IR and it worked OK. The filter function is
called in a Performer 2.1 application, from the draw process.
The source code looks like this:

// read and filter an RGBA (xsize, ysize) image from framebuffer

unsigned long *scrbuf = (unsigned long *) pfMalloc(xsize*ysize*sizeof(long),
    NULL);
glEnable(GL_CONVOLUTION_2D_EXT);
glReadBuffer(GL_FRONT) // or any buffer you like

// find allowed dimensions for filter:
int max_width, max_height;
glGetConvolutionParameterivEXT(GL_CONVOLUTION_2D_EXT,
    GL_MAX_CONVOLUTION_WIDTH_EXT, &max_width);
glGetConvolutionParameterivEXT(GL_CONVOLUTION_2D_EXT,
    GL_MAX_CONVOLUTION_HEIGHT_EXT, &max_height);

// create the filter array
float *filter = new float[max_width * max_height * 3];
for (int i = 0; i < filter_width * filter_width; i++) {
        filter[i * 3] = <something>
        filter[i * 3 + 1] = <something>
        filter[i * 3 + 2] = <something>
}
// set filter RGB format and some parameters ...
glConvolutionParameteriEXT(GL_CONVOLUTION_2D_EXT,
    GL_CONVOLUTION_BORDER_MODE_EXT, GL_REDUCE_EXT);
glConvolutionFilter2DEXT(GL_CONVOLUTION_2D_EXT, GL_RGB,
    max_width, max_height, GL_RGB, GL_FLOAT, (GLvoid *) filter);

// perform reading and filtering at point (xorg, yorg)
glReadPixels((short)xorg, (short)yorg, (short)xsize, (short)ysize, GL_RGBA,
    GL_UNSIGNED_BYTE, scrbuf);

// size of filtered pixel array:
xsize -= max_width - 1;
ysize -= max_height - 1;

Espiero que eso te puede ayudar ...

L.A.

-- 
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Laurent Ach                              tel :  33 (0) 1 41 48 06 60
SYSECA                                   fax :  33 (0) 1 41 48 06 81
ach++at++syseca.fr
http://www.syseca.thomson-csf.com/english/cha1/SDA.HTM
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