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Re: Re-draw of sub-views
- To: firstname.lastname@example.org
- Subject: Re: Re-draw of sub-views
- From: email@example.com (Bill St. Clair)
- Date: Mon, 10 Aug 1992 17:25:02 -0500
- Cc: info-mcl
>For some time now, I have noticed excessive redraw for sub-views.
>My understanding, from my limited Inside Mac library, was that a window has
>update region into which #_InvalRect and #_InvalRgn accumulate.
>As near as I can figure, MCL has broken with this practice and is doing
>something else entirely.
>Whatever this method is, it seems to be extremely expensive for the drawing
>sub-views. Specifically, sub-views seem to be re-drawn when it is totally
>un-necessary. This is bad for dialogs with many and/or complex sub-views.
>Today, I thought I would look into this and see if I could patch it.
>Unfortunately I was...a little too successful. Now I have sub-views that
>won't redraw at all when a window is uncovered.
>But I am hoping somebody out there understands the window-redrawing system
>of MCL and/or the Mac and can tell me where to put calls to #_InvalRect to
>finish this patch. I know I'm being overly simplistic here, but I'm
>The half-patch is commented out so that the problem can be seen first...
This excessive redrawing happens only for SIMPLE-VIEW's. If you put your
SEQUENCE-DIALOG-ITEM inside of a VIEW, it will not be redrawn unless
necessary. A SIMPLE-VIEW is drawn with its container's clip region, so
we can't do any optimization unless we assume that the VIEW-DRAW-CONTENTS
method won't draw outside of the VIEW-CORNERS of the view. I can work up
a patch that will make that assumption if you'd like, but I'm not entirely
convinced that it is the right way to go for everybody. If you have a large
number of subviews of your window, your redrawing will benefit from adding
a little hierarchy so that there are never more than a few views at any level.
Then view-draw-contents can quickly figure out that a VIEW and all of its
subviews do not need to be redrawn.
Sometimes I wish that I had never added SIMPLE-VIEW's to MCL. I think they
speed up redrawing, but the cognitive overload may not be worth it.