NAME

draw: example - simple program illustrating image primitives

DESCRIPTION

This manual page presents a self-contained simple program that illustrates most of the feature of the basic draw library. It must be run at the top-level Inferno shell prompt, not within a window system, as it establishes its own connection to the display and writes directly on the display, not in a private window.

The program exercises the drawing primitives, taking particular care to maintain a consistent coordinate system for the combinations of images on the display. Comments in the code introduce each step.

implement Test;
include "sys.m";
include "draw.m";
Test: module
{
	init:	fn(ctxt: ref Draw->Context, argv: list of string);
};
init(nil: ref Draw->Context, nil: list of string)
{
	sys := load Sys Sys->PATH;
	draw := load Draw Draw->PATH;
	Display, Font, Rect, Point, Image, Screen: import draw;
	#
	# Set up connection to display and initialize colours.
	#
	display := draw->Display.allocate(nil);
	disp := display.image;
	red := display.color(Draw->Red);
	blue := display.color(Draw->Blue);
	white := display.color(Draw->White);
	yellow := display.color(Draw->Yellow);
	#
	# Paint the screen red.
	#
	disp.draw(disp.r, red, nil, disp.r.min);
	sys->sleep(5000);
	#
	# Texture a region with rectangular tiles.
	#
	texture := display.newimage(((0,0),(2,3)),
		disp.chans, 1, Draw->Black);
	texture.clipr = ((-10000,-10000),(10000,10000));
	# put something in the texture
	texture.draw(((0,0),(1,3)), white, nil, (0,0));
	texture.draw(((0,0),(2, 1)), white, nil, (0,0));
	# use texture as both source and mask to let
	# destination colour show through
	disp.draw(((100,100),(200,300)), texture,
		texture, (0,0));
	sys->sleep(5000);
	#
	# White-out a quarter of the pixels in a region,
	# to make the region appear shaded.
	#
	stipple := display.newimage(((0,0),(2,2)),
				disp.chans, 1, Draw->Transparent);
	stipple.draw(((0,0),(1,1)), display.opaque,
				nil, (0,0));
	disp.draw(((100,100),(300,250)), white,
				stipple, (0,0));
	sys->sleep(5000);
	#
	# Draw textured characters.
	#
	font := Font.open(display, "*default*");
	disp.text((100,310), texture, (0,0), font,
			"Hello world");
	sys->sleep(5000);
	#
	# Draw picture in elliptical frame.
	#
	delight := display.open("/icons/delight.bit");
	piccenter := delight.r.min.add(delight.r.max).div(2);
	disp.fillellipse((250,250), 150, 50,
		delight, piccenter);
	disp.ellipse((250,250), 150, 50, 3, yellow, (0,0));
	sys->sleep(5000);
	#
	# Draw a parabolic brush stroke using an elliptical brush
	# to reveal more of the picture, consistent with what's
	# already visible.
	#
	dx : con 15;
	dy : con 3;
	brush := display.newimage(((0,0),(2*dx+1,2*dy+1)), disp.chans,


                               0, Draw->Black);
	brush.fillellipse((dx,dy), dx, dy, display.white,
				(0,0));
	for(x:=delight.r.min.x; x<delight.r.max.x; x++){
		y := (x-piccenter.x)*(x-piccenter.x)/80;
		y += 2*dy+1;	# so whole brush is visible at top
		xx := x+(250-piccenter.x)-dx;
		yy := y+(250-piccenter.y)-dy;
		disp.gendraw(((xx,yy),(xx+2*dx+1,yy+2*dy+1)),


                       delight, (x-dx, y-dy), brush,
			(0,0));
	}
}