colorwheel.js: Example on using Canvas to produce the color wheel.

ariya · Feb 17, 2011 · e158345 · e158345
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diff --git a/ChangeLog b/ChangeLog
@@ -18,6 +18,8 @@ Version 1.1.0
 
     Fixed issue #14: enable or disable plugins (Ariya Hidayat).
 
+    Added a new example: using Canvas to produce the color wheel (Ariya Hidayat).
+
 2011-01-17: Version 1.0.0
 
     Initial launch.

diff --git a/examples/colorwheel.js b/examples/colorwheel.js
@@ -0,0 +1,52 @@
+if (phantom.state.length === 0) {
+    phantom.state = 1;
+    phantom.viewportSize = { width: 400, height : 400 };
+    phantom.content = '<html><body><canvas id="surface">' +
+        '</canvas></body></html>';
+} else {
+    var el = document.getElementById('surface'),
+        context = el.getContext('2d'),
+        width = window.innerWidth,
+        height = window.innerHeight,
+        cx = width / 2,
+        cy = height / 2,
+        radius = width  / 2.3,
+        imageData,
+        pixels,
+        hue, sat, value,
+        i = 0, x, y, rx, ry, d,
+        f, g, p, u, v, w, rgb;
+
+    el.width = width;
+    el.height = height;
+    imageData = context.createImageData(width, height);
+    pixels = imageData.data;
+
+    for (y = 0; y < height; y = y + 1) {
+        for (x = 0; x < width; x = x + 1, i = i + 4) {
+            rx = x - cx;
+            ry = y - cy;
+            d = rx * rx + ry * ry;
+            if (d < radius * radius) {
+                hue = 6 * (Math.atan2(ry, rx) + Math.PI) / (2 * Math.PI);
+                sat = Math.sqrt(d) / radius;
+                g = Math.floor(hue);
+                f = hue - g;
+                u = 255 * (1 - sat);
+                v = 255 * (1 - sat * f);
+                w = 255 * (1 - sat * (1 - f));
+                pixels[i] = [255, v, u, u, w, 255, 255][g];
+                pixels[i + 1] = [w, 255, 255, v, u, u, w][g];
+                pixels[i + 2] = [u, u, w, 255, 255, v, u][g];
+                pixels[i + 3] = 255;
+            }
+        }
+    }
+
+    context.putImageData(imageData, 0, 0);
+    document.body.style.backgroundColor = 'white';
+    document.body.style.margin = '0px';
+
+    phantom.render('colorwheel.png');
+    phantom.exit();
+}