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From: dillon@CORY.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.amiga
Subject: Re: Rapid Stimulus Displaying on the Amiga Help.  Solution
Message-ID: <8704200221.AA03819@cory.Berkeley.EDU>
Date: Sun, 19-Apr-87 21:21:03 EST
Article-I.D.: cory.8704200221.AA03819
Posted: Sun Apr 19 21:21:03 1987
Date-Received: Sun, 19-Apr-87 23:46:00 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 41


	Use a two plane screen, then render bitmap A into plane 1, and 
	bitmap B into plane 2 .  The idea is that then all you need to
	do to switch bitmaps is set the color registers:

	plane:	2 1	color register
		0 0	0	always background color
		0 1	1	depends 
		1 0	2	depends
		1 1	3	doesn't matter

	Step 1:	Set all color registers to background color
	Step 2: Render bitmap A into plane 1
		Render bitmap B into plane 2
			(user still sees background color)
		
	Remember that when you do a SetRGB4(), the new colors don't take
	effect until the vertical retrace gets back to the top (and the
	Copper reloads the color registers).

	Step 3: WaitTOF(), set register 1 = COLOR, 2 = BACKGROUND
		(user still sees background since you missed the copper reload)
	Step 4: WaitTOF(), set register 1 = BACKGROUND, 2 = COLOR
		Here, the copper had just loaded 1 = COLOR, 2 = BACKGROUND,
		so the user sees plane 1.  On the next retrace, the user will
		see plane 2.

	Step 5: WaitTOF(), set register 1 = COLOR, 2 = BACKGROUND
		Again, even though you're using SETRGB4() to set the color,
		it happens AFTER the copper has loaded the color registers.

		continue this way until done.
		

	The real neat thing about this method of doing things is that your
	process has an entire 1/60th of a second after the WaitTOF() returns 
	to make the changes to the colormap with SetRGB4().  Needless to say,
	this means you can run the program without a Forbid()/Permit().

					-Matt