<p>Get Processing from <a href="https://processing.org">processing.org</a>. Download, extract, and launch. On Linux, just click the <code>processing</code> file.</p>
<p>Processing requires that <em>either</em> OpenJDK or Java to be installed.</p>
<p>Processing requires a <code>void setup()</code> function, which is a function that Processing expects whenever an application is launched. If you don't have a <code>setup</code> function, your application still launches, but with basic Processing defaults. Try this to start with:</p>
<pre><code>void setup() {
    size(480,720);
}</code></pre>
<p>Click the <strong>Run</strong> button in the top left corner to launch your [very simple] application: an empty window that is 480 pixels wide and 720 pixels tall.</p>
<p>Draw a rectangle on your canvas by invoking Processing's <code>void draw()</code> function:</p>
<pre><code>void draw() {
    rect(10,10,80,80);
}</code></pre>
<p>Click the <strong>Run</strong> button in the top left corner to launch your application.</p>
<p>Add some colour to your rectangle:</p>
<pre><code>void draw() {
    fill(8,120,90);
    rect(10,10,80,80);
}</code></pre>
<p>Click the <strong>Run</strong> button in the top left corner to launch your application.</p>
<p>Make a simple painting app:</p>
<pre><code>void setup() {
    size(480,720);
}

void draw() {
    if (mousePressed) {
        fill(20,120,90);
        ellipse(mouseX,mouseY,25,25);
    } else {
        fill(random(10,120),random(10,80),random(20,200));
    }
}</code></pre>
<p>More Processing tricks: you can export your application as a standalone Java app, or as an Android <code>.apk</code> as long as you have the Android SDK installed.</p>
<p>Processing's <a href="https://processing.org/reference">documentation</a> is excellent. It has examples for all functions, <em>with pictures</em>.</p>
