🚀 go-pugleaf

I experimented with offscreen pixmaps today. It seems that Color
Quickdraw is very flexible, but too slow for good animation. Most of the
overhead comes from color matching and conversion. I guess I could write
my own color matching routine, but I think there should be a fast way to
do a simple copy operation.

In most painting programs the actual painting could be done on an
offscreen bitmap with the same color table as the best gDevice.

It takes about twice as much time to do a copybits in srcCopy mode than
it takes in the srcXor mode. Below is a short program that draws to an
offscreen pixmap and then copies it back to the screen. Try different
transfer modes and note the speed difference. The code is written in LS
C 2.13. Even srcXor, which is the fastest usable mode, is too slow for
really high quality animation.

How can it be done faster?

#include <MacTypes.h>
#include <QuickDraw.h>
#include <Color.h>
#include <WindowMgr.h>

WindowPtr	onScreen;
CGrafPtr	offS;
RGBColor	temp;
PixMapPtr	offP;

void	main()
{
	int	i;
	
	InitGraf(&thePort);	InitCursor();
	InitFonts();		InitWindows();
		
	onScreen=GetNewWindow(1000,0L,-1);

	offS=(CGrafPtr)NewPtr(sizeof(*offS));

	OpenCPort(offS);
	HLock(offS->portPixMap);
	offP=*(offS->portPixMap);

	SetRect(&offP->bounds,0,0,256,256);
	PortSize(256,256);
	offP->rowBytes=32768L+256;

	offP->baseAddr=NewPtr(65536L);

	EraseRect(&offS->portRect);
	temp.blue=65535;
	temp.red=0;
	temp.green=0;
	RGBForeColor(&temp);
	for(i=0;i<256;i+=4)
	{	MoveTo(i,0);
		LineTo(255-i,255);
	}

	SysBeep(10);
	HideCursor();
	for(i=100;i;i--)
		CopyBits(&((GrafPtr)offS)->portBits,&onScreen->portBits,
				 &offS->portRect,&offS->portRect,srcXor,0);
	SysBeep(10);
	while(!Button());
}

Juri Munkki
jmunkki@santra.hut.fi
jmunkki@fingate.bitnet
lk-jmu@finhut.bitnet

P.S. The window is longword aligned and a color table was copied from the
     system file.