On Monday 31 January 2005 18:01, Daniel Phillips wrote: > Of course. However, this is just an optimized way of dividing several > parameters. For perspective interpolation you have to interpolate the > inverses of the parameters, and divide by the interpolated inverse of > W. This does not appear to be handled correctly in the model.
The formula for perspective correct interpolation is:
f = F(t) / M(t), where F(t) = (1-t)f_0/w_0 + tf_1/w_1 and
M(t) = (1-t)/w_0 + t/w_1
Both F and M can be linear interpolated, and before the actual fragment
pipeline is entered, divide F/M.
This is exactly what the software model does already, only that M is called
W.
There's really nothing wrong with perspective correction in the software
model as far as I can see, the problem lies with Z as I explained in the
other thread ("Depth buffer"). Nobody has taken up the challenge of
figuring out how to do orthographic projection correctly with the current
software model (I'm saying it can't be done, because where OpenGL specifies
two independent variables, the software model only has one).
cu,
Nicolai
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