/*
 *  Smiley
 *  ------
 *  This program draws a smiley inside a window. It uses a drawing
 *  area with a redraw call-back function to ensure the smile is
 *  always drawn.
 *
 *  Note there is a problem with this program: if you resize the
 *  window to be too small, it hangs there forever. Why?
 *  The answer is in the drawarc function drawing the smile.
 *  If the face rectangle r1 gets too small, r2 (which is r1 inset
 *  by 30 pixels) gets a negative width and/or height.
 *
 *  Negative-sized rectangles are no good. The computer hardware
 *  treats rectangle widths and heights as unsigned integers.
 *  A negative number when cast to an unsigned int becomes very large
 *  indeed. The graphics hardware is then trying to draw an impossibly
 *  large arc, hence the program sits there drawing for a long time.
 *
 *  Solution? Add this line before drawarc: r2 = rcanon(r2);
 *  The rcanon function corrects for negative widths and/or heights
 *  and makes them positive again, while preserving the size of the
 *  rectangle.
 */

#include <graphapp.h>

void draw_smile(drawing d, rect r)
{
	rect r1 = insetr(r, 10);	/* inset r1 from edge of drawing */
	rect r2;
	point p;

	setcolour(LightBlue);		/* blue face */
	fillellipse(r1);		/* draw face */

	setcolour(Red);			/* red lips */
	setlinewidth(2);		/* thicker lips */
	r2 = insetr(r1, 30);		/* inset from face rectangle */
	drawarc(r2, 270-60, 270+60);	/* smile between arc angles */

	setcolour(Brown);		/* brown eyes */
	p.x = r1.x + r1.width  * 1/2;
	p.y = r1.y + r1.height * 1/4;

	r2 = rect(p.x - 30, p.y, 20,20);
	fillellipse(r2);		/* draw left eye */

	r2 = rect(p.x + 10, p.y, 20,20);
	fillellipse(r2);		/* draw right eye */
}

void resize_smile(window w, rect r)
{
	/* retrieve remembered drawing */
	drawing d = (drawing) getdata(w);
	resize(d, r);
}

void main(void)
{
	window w;
	drawing d;

	w = newwindow("Smile!", rect(50,50,120,120), StandardWindow);
	d = newdrawing(rect(0,0,120,120), draw_smile);
	setdata(w, d);	/* store the pointer with the window */
	setresize(w, resize_smile);
	show(w);
	mainloop();
}