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From: robert@shangri-la.gatech.edu (Robert Viduya)
Newsgroups: comp.windows.x
Subject: fast, flicker-free animation, how?
Message-ID: <16223@hydra.gatech.EDU>
Date: 1 Nov 90 18:42:26 GMT
Sender: news@prism.gatech.EDU
Organization: Office of Information Technology, Georgia Tech
Lines: 39

I'm working on a program that animates some simple geometric entities and
displays them in a window and I'm having trouble getting X to update quickly.
The environment is a Sun SparcStation I with a cg3 (8-bit plain framebuffer)
running OpenWindows 2.0.  Drawing the entities doesn't take any significant
time but getting X to display them quickly seems to be a big stumbling block.
I've tried three different methods:

	Draw directly into the window, clearing it to the background color
	before starting to draw.  This is the fastest and I get about 14
	frames per second.  However, because of the clearing and redrawing,
	the window flickers rather annoyingly.

	Draw into an offscreen pixmap and then use XCopyArea to put it
	into the window.  This is the slowest and I get about 4 frames
	per second.  It does, however, produce no annoying flicker.

	Split the 8-bit deep window into two overlapped 4-bit deep buffers
	and create two colormaps; the first displays the first 4-bit deep buffer
	and maps the second to the background color and the second colormap
	displays the second 4-bit deep buffer and maps the first to the
	background color.  To draw an image, first load the colormap that
	displays the buffer you are NOT going to draw into, then set the
	gc planemasks to the buffer your are going to draw into.  When done,
	swap the colormaps and planemasks.  This produced about 6 frames
	per second with the annoying side effect of causing all other
	windows on the X screen to flicker like crazy because of the colormap
	switching.  It may have worked even faster if the window manager
	wasn't involved (the window manager is the program who's responsible
	for installing colormaps into the server, X clients submit requests
	to the window manager to have their colormaps installed).

Has anyone got any other techniques to try?

			robert
--
Robert Viduya					   robert@shangri-la.gatech.edu
Technical Services / Office of Information Technology
Georgia Institute of Technology					 (404) 894-6296
Atlanta, Georgia	30332-0275