|Subject:||Re: two-pixel trace left when move overlay|
|Date:||Mon, 24 Apr 2006 11:45:18 +0100|
|User-agent:||Thunderbird 18.104.22.168 (Windows/20060308)|
Kim F. Storm wrote:
It is almost certainly due to this change:"Drew Adams" <address@hidden> writes:I have an overlay in buffer *Completions* to highlight the current candidate during cycling of candidates in the minibuffer. I use this code to reposition the overlay: (if (symbol-value overlay) (move-overlay (symbol-value overlay) start end buffer) (set overlay (make-overlay start end buffer)) (overlay-put (symbol-value overlay) 'face face)) In Emacs 20, 21, and a CVS snapshot of June 26, 2005, this works OK. In a CVS snapshot of 2006-03-20, when I move the overlay, a two-pixel (I believe) trace is left behind. See attached screenshots.Hi Drew, I tried to reproduce this with the files you sent me (I had to get hexrgb.el from the wiki), but I don't see the problem on X/GNU/Linux. Perhaps it is a Windoze specific problem?
2005-07-01 Jason Rumney <address@hidden>
* w32term.c (cleartype_active): New flag for enabling sub-pixel
(w32_initialize): Initialize it.
(w32_native_per_char_metric): Allow a couple of extra pixels when
Cleartype is active.
* w32term.c (w32_initialize): Move check for screen reader here
The history of this is:
In Windows XP, "Cleartype" sub-pixel anti-aliasing was introduced. With some fonts, this caused a garbaged display, since characters draw outside of their advertised bounding box.
In 21.3 I disabled the use of Cleartype in Emacs to avoid this problem, but users complained, so a workaround of increasing the width of the bounding box by one pixel left and right was installed. This should cause Emacs to always draw a whole line at a time (after figuring out that characters on that line are overlapping), which is the advice that Microsoft gives to avoid this problem.
I guess the workaround must be adversely affecting the drawing of overlays though - the extra two pixels being drawn on the background, but not detected when it comes time to erase them.
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