ref: b5bc6572b0a82c52ab04bcf25e1ed76700deb246
dir: /man/2/draw-example/
.TH DRAW-EXAMPLE 2
.SH NAME
draw: example \-
simple program illustrating image primitives
.SH 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.
.PP
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.
.PP
.EX
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));
}
}
.EE