Re: [Mesa3d-dev] Inconsistent scan conversion in XOR mode

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

Howard wrote:
> 
> Has anyone else observed a problem with the scan conversion of vertical and
> horizontal lines while in XOR mode. We have consistently observed that there
> are:
> a) Irregularities in vertical and horizontal line, i.e. 4 - 10 pixel spans
> that are offset by a pixel.
> b) Non repeating patterns, i.e. the same vertical or horizontal line
> coordinates plot these irregularities differently. This is especially
> visible/troublesome in the XOR case, because the 2nd, (erase) draw does not
> cover the same pixels, and consequently leaves scars. This only seems to
> happen in the vertical/horizontal cases and does not happen when in a
> normal, (non XOR) mode.

I've seen a problem in which a clipped, vertical, wide line will "wiggle"
left/right by a pixel.  When I looked into it it was a case where one
endpoint was at X=5 and the other at x=4.999 (for example).

Are your endpoints being clipped?

-Brian