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     DRAW-EXAMPLE(2)                                   DRAW-EXAMPLE(2)

     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);

               #

     DRAW-EXAMPLE(2)                                   DRAW-EXAMPLE(2)

               # 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,

     DRAW-EXAMPLE(2)                                   DRAW-EXAMPLE(2)

                                         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));
               }
          }