Re: "Bold" effect when anti-aliased glyphs are overwritten

[Chong Yidong <cyd@stupidchicken.com>]

Chong Yidong <cyd@stupidchicken.com> writes:

> I've been noticing that glyphs near the cursor occasionally become
> "bold" for no reason.
>
> The reason this happens is that when the redisplay engine calls
> draw_glyphs to draw certain glyphs, such as the cursor glyph,
> neighboring glyphs are redrawn if there is a left or right overhang
> (xdisp.c:19929).
>
> With anti-aliasing, it doesn't work well.  Apparently, during the
> anti-aliasing calculation, the entire existing glyph---including the
> glyph foreground---is treated as the "background".  Thus, the
> anti-aliased parts of the foreground character becomes more and more
> prominent, and eventually saturates completely.

I've checked in a fix into CVS.  Please let me know if it causes any
problems.