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Painting Widgets with Seesaw

The functionality describe here will be in the 1.0.7 release of Seesaw in the next week or so.

Say for some reason, you want a label with a red X on it. A bad, bad label. If you’re working with Swing in Java, you’ll create a new class, extend JLabel, override paintComponent, make some drawing calls, etc. Not terrible, but not that fun either. Something like this:

public class BadLabel extends JLabel {
  public BadLabel(String text) {
  public void paintComponent(Graphics g) {
    final int w = getWidth();
    final int h = getHeight();
    final int d = 5;
    g.drawLine(d, d, w - d, h - d);
    g.drawLine(w-d, d, d, h - d); 

That’s pretty minimal if we ignore imports and stuff. Enabling anti-aliasing would be nice. It’d also be nice to set the width of the lines. And if you wanted to draw the X on a button or something else, you could pull all the drawing code into a function, but you couldn’t avoid a new, possibly anonymous, class for each type of component you want to use it on.

In Seesaw, we use the paintable macro to do all the dirty work for us. Give it a function to handle the painting and a description of the widget you want, and you’re done. It handles anti-aliasing and there’s functions that make styling the lines a little less tedious.

Below is the equivalent Clojure code using Seesaw. Note that here we can easily apply the red X to a label or a button. Of course this also puts the widgets in a frame and displays them too. I’ll spare you that part in Java :)

The code for this example is also here.

(ns seesaw.examples.paintable
  (:use [seesaw core graphics]))

(defn draw-a-red-x 
  "Draw a red X on a widget with the given graphics context"
  [c g]
  (let [w          (width c)
        h          (height c)
        line-style (style :foreground "#FF0000" :stroke 3 :cap :round)
        d 5]
    (draw g
      (line d d (- w d) (- h d)) line-style
      (line (- w d) d d (- h d)) line-style)))

(defn content []
    :border 5
    :items [
      (label           :text "I'm a good label!" :font "ARIAL-BOLD-40" :foreground "#00AA00")
      ; *** Make a label and button with a red X on them ***
      (paintable label :text "I'm a bad label!"  :font "ARIAL-BOLD-40" 
                              :paint draw-a-red-x)
      (paintable button :text "I'm a bad button!"  :font "ARIAL-BOLD-40"
                                :paint draw-a-red-x)]))

(defn -main [& args]
      (frame :title "Seesaw (paintable) example"
             :content (content))

(paintable) is still a macro so it comes with all the limitations associated with them. Unfortunately with Swing you have to sub-class to paint on a widget and in Clojure you can’t (as far as I know) sub-class at run-time.

Categories: clojure, seesaw, swing Tags: , ,
  1. Devin Walters
    March 25th, 2012 at 18:08 | #1

    Note that “paintable” is now deprecated.

    The docstring states that you should just you :paint directly on any widget.

    In addition, you want to use (seesaw.core/canvas) if you just want a panel to draw on.

    Again according to the docstring: Note that *all* seesaw widget types support :paint.

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