Re: [Mesa3d-dev] X renderer speedup (write_span_mono_pixmap optimization)

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

Jeff Epler wrote:
> 
> I'm currently trying to move an older piece of software from using
> PEX/X11 to Mesa/X11.  (We use(d) a modified version of PEX with zbuffer
> support, and it's becoming too much of a chore to propogate these
> patches to new versions of XFree86)
> 
> Our software draws exclusively flat-shaded, zbuffered polygons.
> 
> Out of the box (Mesa 3.2/RedHat 6.2) or using Mesa 3.4.1, the Mesa
> renderer is rather slower than our PEX-based renderer.  However, a
> simple change to write_span_mono_pixmap brings the two renderers to
> nearly equal speed.
> 
> Basically, we discovered in past iterations of software renderers that
> coalescing as many pixels as possible into single X calls is a very
> important optimization (in fact, another dead renderer actually unifies
> multiple single-color spans into a single XDrawSegments call).
> write_span_mono_pixmap performs this optimization using
> XMesaFillRectangle when no pixels in the span were excluded (due to
> depth check or other factors)
> 
> However, if any pixels were excluded, then it falls back to
> XMesaDrawPoint for all points.
> 
> This patch accumulates consecutive "drawn" pixels into a single
> XMesaFillRectangle call.  This is a big speed boost in our application,
> and a slight pessimization in the case of e.g., a 50% stipple.
> (XFillRectangle is likely to be optimized for the 1x1 case, as well as
> the Nx1 case)  A slightly more intelligent patch would probably
> disable the optimization for very short spans, or spans with large
> numbers of sub-spans.
> 
> I'll include the patch in my message.  Is submitting it to the
> sourceforge patch tracker appropriate?  It doesn't look like that SF
> feature is well-used.

Sending small patches to this list is fine.  Larger patches should
be filed on SF.

I'll look this over and probably apply it soon.  Thanks!

-Brian