[9fans] graphics

[andrey mirtchovski <aam396@mail.usask.ca>]

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hi,

i spent the weekend trying to learn more about the plan9 graphics model and
trying to write a simple program (started off with russ cox' click.c and
worked on top of it) and i must say i am quite impressed with the ease with
which programs are created, relative size, simplicity and speed...

included is a simple program that emulates one of the x-screensavers by
drawing random squares in the window it is started in... one can use it
mostly for speed-evaluation and/or to tell me if there is any problem with
terminals running in less-than-24 bit mode...


several questions popped up while i was implementing it:

	the 'eresized()' routine seems not to be called if the program is not
	waiting on any event. e.g. in one of my earlier implementations i lacked
	a call to ecanread/emouse/emenuhit in the main loop and as a side effect
	eresized was not called when the window was moved... it only started
	working after i added (any) of the abovementioned function calls.

	it is possible to force the machine to reboot if one mistakingly forgets
	to free the allocimagemix pointer after the recangle is drawn... this seems
	to be a big problem, because i've always assumed a runaway process that
	takes up the entire memory would just be terminated instead of causing
	the machine to reboot... or maybe plan9 does things in a different way?
	:)


well.. comments/flames are welcome :)


cheers: andrey


PS: obligatory screenshot of plan9 in 'working condition' is available from

	http://homepage.usask.ca/aam396/scrsht.gif

you can see my irc client running in the bottom left corner of the screen,
the language spoken is bulgarian (transliterated)...

the entire page is not operational though, i'm just using it for this
screenshot...
	

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/* draw random rectangles in the current window
* sort of like the xscreensaver we all know
* -- andrey
*/

/* based on russ cox' click.c */


#include <u.h>
#include <libc.h>
#include <draw.h>
#include <thread.h>
#include <event.h>

int minx, miny, maxx, maxy;

void
eresized(int new)
{
	Rectangle r;
	if(new && getwindow(display, Refnone) < 0)
		fprint(2,"can't reattach to window");
	r = screen->r;
	minx = r.min.x;
	miny = r.min.y;
	maxx = r.max.x;
	maxy = r.max.y;
	draw(screen, screen->r, display->white, nil, ZP);
}

void
main(int argc, char **argv)
{
	Mouse m;
	Image *img;
	Rectangle r;
	int i;
	int slp = 10;

	char *items[] = { "slower", "faster", "exit", nil };


	Menu menu;

	/* setup menus */
	menu.item = items;
	menu.gen = nil;

	srand(0);

	initdraw(0,0,"whoopty doo");
	eresized(0);
	einit(Emouse);


	for(;;){
		if(ecanmouse())	{
			m = emouse();
			if(m.buttons & 4) {
				switch(emenuhit(3, &m, &menu)) {
					case 0: 	slp += 10; break;
					case 1: 	if(slp) 
									slp -= 10;
								else 
									slp = 0; 
								break;
					case 2: 	exits("user abort");
					default: 	fprint(2, "impossible button\n");
				}
			}
		}
		
		/* draw a rectangle somewhere in the window */
		/* make sure rectangle does not overflow window */
		r.min.x = minx + nrand(maxx - minx);
		r.min.y = miny + nrand(maxy - miny);
		r.max.x = r.min.x + nrand(maxx - r.min.x);
		r.max.y = r.min.y + nrand(maxy - r.min.y);

		/* get a random color and random alpha for drawing */
		/*** probably not the best way of doing it ***/
		img = allocimagemix(display,nrand(256)<<24 | nrand(256) << 16 | nrand(256) <<8 | (256 - nrand(256)),nrand(256)<<24 | nrand(256) << 16 | nrand(256) <<8 | (256 - nrand(256)));

	 	draw(screen, r, img, nil, ZP);
		flushimage(display, 1);
		freeimage(img);
		/* slow down the drawing somehow */
		sleep(slp);
	}
}