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From: mouse@lightning.mcrcim.mcgill.EDU (der Mouse)
Newsgroups: comp.windows.x
Subject: Re: Remembering Graphics
Message-ID: <9103260339.AA04253@lightning.McRCIM.McGill.EDU>
Date: 26 Mar 91 03:39:19 GMT
Sender: tytso@athena.mit.edu (Theodore Y. Ts'o)
Organization: The Internet
Lines: 38

>> [An application which displays image data in a window (actually a
>> pixmap which is then copied to the window upon exposure) and then
>> draws some lines and text over the image.  When the image changes,
>> is there any way to avoid having to recompute/redraw the text and
>> lines which are independant of the image data?]

>> - We have thought about have text/lines in one Pixmap and the image
>>   in another Pixmap and then combining them together [...].

> What you can do is have a pixmap for the image data.  Also have a
> _bitmap_ (a 1 bit deep pixmap) into which you will draw the text and
> lines.  To get the image & text/lines into a window you use
> XCopyArea() to copy the image data from the pixmap and then use
> XCopyPlane() to copy from the bitmap into the window.  The GC used in
> XCopyPlane() should:

> 	o Have the clipmask set to the bitmap which is the source of
> 	  the XCopyPlane() call.

If you do that, you don't need to XCopyPlane(); you can
XFillRectangle() instead.

Note that you need to reset the clip-mask every time, if you've drawn
into it since you last set it; you can't depend on the GC noticing
changes you make to the bitmap after you set it as the clip-mask.

The original poster also said (in text I've deleted) that they're using
colormap cells 0-8 for annotations.  This implies more than one bit's
worth of annotations.

Possibilities: keep a separate bitplane for each color of annotation,
which you suggested, or perhaps keep a pixmap for annotations and then
XCopyArea() it using your notion of an appropriate clip-mask in the GC.

					der Mouse

			old: mcgill-vision!mouse
			new: mouse@larry.mcrcim.mcgill.edu