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);
ones := display.ones;
 #
# Paint the screen red.
#
disp.draw(disp.r, red, ones, disp.r.min);
sys->sleep(5000);
 #
# Texture a region with rectangular tiles.
#
texture := display.newimage(((0,0),(2,3)), disp.ldepth, 1, 0);
texture.clipr = ((-10000,-10000),(10000,10000));
# put something in the texture
texture.draw(((0,0),(1,3)), blue, ones, (0,0));
texture.draw(((0,0),(2, 1)), blue, ones, (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.ldepth, 1, 0);
stipple.draw(((0,0),(1,1)), ones, ones, (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.ldepth,
                               0, 0);
brush.fillellipse((dx,dy), dx, dy, ones, (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));
}
}

Plan 9  —  June 29, 2000