Re: [Mesa3d-dev] s_texture.c

[Brian P. <br...@va...>]

Daniel Vogel wrote:
> 
> On Thu, Dec 14, 2000 at 10:16:58AM -0700, Brian Paul wrote:
> >
> > Are you settting GL_TEXTURE_BASE_LEVEL?
> 
> No, I only set GL_TEXTURE_MAX_LEVEL and cut off the last two mip levels.
> It also looks like the filters use the wrong base mipmap. Everything
> looks overblurry from an angle and a naive guess would be that it's
> taking everything 2 levels too far down.
> 
> > I think I see an error in the calculation in _P.  I think I should
> > add the base level to it.  However, that would increase _P.
> 
> from mtypes.h:
> 
>    GLint _P;                    /* Highest mipmap level */
>    GLfloat _M;                  /* = MIN(MaxLevel, P) - BaseLevel */
> 
> What do _P and _M actually mean? Is _P the highest mip level based on
> the size of the image (e.g. 5 for 32x32) and _M supposed to be the one
> after "clipping"?

I should rename _P to _q (which is what the 1.2 spec uses now).  q is the
highest-numbered mipmap level that can actually be used, after taking in
account the image sizes and the value of GL_TEXTURE_MAX_LEVEL.

_M is the max usable lambda value.  It should be = _MaxLevel - BaseLevel.
If you're looking at equation 3.21 in the 1.2 spec, then _M = q - b.  I
should probably rename that variable too (_MaxLambda).

The incoming lambda value is added to BaseLevel to select a mipmap level.

The idea is that lambda=0 will correspond to the BaseLevel texture
and lambda = _M will correspond to the GL_MAX_LEVEL texture.

I'm not sure why you're seeing blurry images.  I haven't tried running
UT with 3.5 yet.

-Brian