o3d-webgl: Allows non-opaque alpha channel for canvas clearColor

samples/o3d-webgl/client.js

 /*
  * Copyright 2010, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 281 matching lines @@
  * @type {!Array.<!o3d.Pack>}
  */
 o3d.Client.prototype.packs_ = [];
 
 /**
  * Keeps track of all counters associated with this client.
  * @type {o3d.CounterManager}
  */
 o3d.Client.prototype.counter_manager_ = null;
 
+/**
+ * Whether or not the client sets the alpha channel of all pixels to 1 in the
+ * final stage of rendering.
+ *
+ * By default, this is set to true to mimic the plugin's behavior. If
+ * a transparent canvas background is desirable, this should be set to false.
+ *
+ * @type {boolean}
+ */
+o3d.Client.prototype.normalizeClearColorAlpha = true;
 
 /**
  * Function that gets called when the client encounters an error.
  */
 o3d.Client.prototype.error_callback = function(error_message) {
   alert(error_message);
 };
 
 
 /**
@@ skipping 153 matching lines @@
   }
   this.then_ = now;
 
   this.gl.colorMask(true, true, true, true);
 
   this.renderTree(this.renderGraphRoot);
 
   // When o3d finally draws to the webpage, the alpha channel should be all 1's
   // So we clear with a color mask to set all alpha bytes to 1 before drawing.
   // Before we draw again, the color mask gets set back to all true (above).
-  this.gl.colorMask(false, false, false, true);
-  this.gl.clearColor(0.0, 0.0, 0.0, 1.0);
-  this.gl.clear(this.gl.COLOR_BUFFER_BIT);
+  if (this.normalizeClearColorAlpha) {
+    this.gl.colorMask(false, false, false, true);
+    this.gl.clearColor(0.0, 0.0, 0.0, 1.0);
+    this.gl.clear(this.gl.COLOR_BUFFER_BIT);
+  }
 };
 
 
 /**
  * An object for various statistics that are gather during the render tree
  * tranversal.
  *
  * @type {Object}
  */
 o3d.Client.prototype.render_stats = {}
@@ skipping 783 matching lines @@
  * Gets info about the client.
  */
 o3d.Client.prototype.clientInfo = null;
 
 
 /**
  * The canvas associated with this client.
  * @type {Element}
  */
 o3d.Client.prototype.canvas = null;