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researchv10 Dan Cross

.ds ZZ DEVELOPMENT PACKAGE
.TH SCREENSWAP 3R "630 MTG"
.XE "screenswap()"
.SH NAME  
screenswap \- swap screen Rectangle and Bitmap
.SH SYNOPSIS
.ft B
#include <dmd.h>
.sp
void screenswap (b, r, s) 
.br
Bitmap \(**b;
.br 
Rectangle r, s; 
.SH DESCRIPTION
The
.I screenswap
function
does an in-place exchange of the Rectangle
.I r
within the Bitmap
.I b
and screen rectangle
.IR s.
This exchange is done by \fIbitblt\fR'ing the bitmaps back and forth
three times in XOR mode. This technique allows bitmaps to be exchanged
without need for intermediate storage.
.PP
The action of screenswap is undefined, if
.I r
and
.I s
are not the same size.
.PP
.I Screenswap
writes to the
.I physical
bitmap, so the
.I s
argument
is clipped to the screen,
not to the window's rectangle (display.rect).
.SH EXAMPLE
The following program floats a picture of a sailboat
across the screen.
.PP
The 630 MTG mouse cursor is painted in XOR mode and therefore
changes to inverse video when it moves over highlighted areas. This sailboat,
however, does not inverse video when it moves over parts of the
screen that are highlighted. This is accomplished by saving
whatever is on the screen in the spot where the sailboat is currently
painted and restoring the screen when the sailboat moves. The unique
aspect of this is that the same physical memory is used to alternately
store the picture of the sailboat and the saved screen rectangle, and
these two bitmaps are swapped without use of intermediate storage.
.PP
.RS 3
.nf
.ft CM
#include <dmd.h>

unsigned short sailicon[] = {
	0xFDFF, 0xF9FF, 0xF1FF, 0xE0FF,
	0xFD7F, 0xF9BF, 0xF5DF, 0xEDEF,
	0xDDF7, 0xDDF7, 0xBDFB, 0xB8FB,
	0x0000, 0x8003, 0xE007, 0xFFFF,
};

Bitmap sailmap = {
	(Word *)sailicon,
	1,
	(short)0, (short)0, (short)16, (short)16,
	(char *)0
};

extern Rectangle fRpt();
extern Rectangle raddp();

main()
{
	Rectangle r;

	r = fRpt(0, YMAX/2-8, 16, YMAX/2+8);

	/* put the sailboat onto the screen */
	screenswap(&sailmap, sailmap.rect, r);

	/* move the sailboat across the screen */
	while(r.corner.x <= YMAX) {
		sleep(3);
		screenswap(&sailmap, sailmap.rect, r);
		r = raddp(r, Pt(1,0));
		screenswap(&sailmap, sailmap.rect, r);
	}

	/* remove the sailboat for the last time */
	screenswap(&sailmap, sailmap.rect, r);
}
\fR
.fi
.RE
.PP
This example is very similar to how message boxes are implemented.
Message boxes are rectangles containing messages which float
around the screen when the mouse moves.
.SH SEE ALSO
bitblt(3R), msgbox(3R).

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