From: Luc Renambot (renambot++at++cs.vu.nl)
Date: 08/15/2002 04:03:01
] -----Original Message-----
] From: w.price++at++electronic-alchemy.co.uk
] [mailto:w.price++at++electronic-alchemy.co.uk]
] Sent: Wednesday, August 14, 2002 16:47
] To: info-performer++at++sgi.com
] Cc: Performer Newsgroup
] Subject: Re: [info-performer] depth buffer write is slow.
]
]
]
] Another possible speedup which I have found across using
] glDrawPixels() on Linux is to NOT send the entire chunk of data
] in one go. i.e. instead of using
]
] glDrawPixels(1024, 768, ....)
]
] use
]
] glRasterPos2i(0, 0);
] glDrawPixels(128, 128, ...., buffer);
] glRasterPos2i(128, 0);
] glDrawPixels(128, 128, ...., buffer + offset);
] .....
] .....
] (most likely this will be in a loop)
Must dependend on the driver and the memory bandwidth of the
system, but on Dual-athlon with GeForce4 under Linux (latest driver),
I don't get any speedup with tiling. The max is always with one
glReadPixels call, with around 90Mpixels/sec. Or I have a bug
im my code (GL_UNPACK_SKIP_PIXELS seems killing the perf,
but otherwise you need a memcopy, no ?).
I tried to swap the indices, or doing by block of rows, it's
not better.
#if 0
glDrawPixels( width, height, GL_RGB, GL_UNSIGNED_BYTE, pixels );
#else
block = 128;
stepi = width / block;
stepj = height / block;
glPixelStorei(GL_UNPACK_ROW_LENGTH, width);
glPixelStorei(GL_UNPACK_IMAGE_HEIGHT, height);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glPixelStorei(GL_UNPACK_SKIP_ROWS, 0);
for (j=0;j<stepj;j++)
for (i=0;i<stepi;i++)
{
glRasterPos2i(i*block,j*block);
glPixelStorei(GL_UNPACK_SKIP_PIXELS, i*block);
glDrawPixels( block, block, GL_RGB, GL_UNSIGNED_BYTE,
pixels + width*j*block*3);
}
#endif
Luc.
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