Added useDepthPicking flag from 3d-tiles

CHANGES.md

@@ -5,6 +5,7 @@ Change Log
 
 * Reduced the amount of CPU memory used by terrain by ~25% in Chrome.
 * Fixed a picking problem ([#3386](https://github.com/AnalyticalGraphicsInc/cesium/issues/3386)) that sometimes prevented objects being selected.
+* Added `Scene.useDepthPicking` to enable or disable picking using the depth buffer. [#3390](https://github.com/AnalyticalGraphicsInc/cesium/pull/3390)
 
 ### 1.17 - 2016-01-04
 

Source/Scene/Scene.js

@@ -500,6 +500,14 @@ define([
          */
         this.fxaa = true;
 
+        /**
+         * When <code>true</code>, enables picking using the depth buffer.
+         *
+         * @type Boolean
+         * @default true
+         */
+        this.useDepthPicking = true;
+
         /**
          * The time in milliseconds to wait before checking if the camera has not moved and fire the cameraMoveEnd event.
          * @type {Number}
@@ -1555,7 +1563,7 @@ define([
             commands.length = frustumCommands.indices[Pass.TRANSLUCENT];
             executeTranslucentCommands(scene, executeCommand, passState, commands);
 
-            if (defined(globeDepth) && environmentState.useGlobeDepthFramebuffer) {
+            if (defined(globeDepth) && environmentState.useGlobeDepthFramebuffer && scene.useDepthPicking) {
                 // PERFORMANCE_IDEA: Use MRT to avoid the extra copy.
                 var pickDepth = getPickDepth(scene, index);
                 pickDepth.update(context, globeDepth.framebuffer.depthStencilTexture);
@@ -2013,6 +2021,10 @@ define([
      * @exception {DeveloperError} 2D is not supported. An orthographic projection matrix is not invertible.
      */
     Scene.prototype.pickPosition = function(windowPosition, result) {
+        if (!this.useDepthPicking) {
+            return undefined;
+        }
+
         //>>includeStart('debug', pragmas.debug);
         if(!defined(windowPosition)) {
             throw new DeveloperError('windowPosition is undefined.');

Specs/Scene/SceneSpec.js

@@ -584,6 +584,40 @@ defineSuite([
         expect(position).toBeDefined();
     });
 
+    it('pickPosition returns undefined when useDepthPicking is false', function() {
+        if (!scene.pickPositionSupported) {
+            return;
+        }
+
+        var rectangle = Rectangle.fromDegrees(-100.0, 30.0, -90.0, 40.0);
+        scene.camera.setView({
+            destination : rectangle
+        });
+
+        var canvas = scene.canvas;
+        var windowPosition = new Cartesian2(canvas.clientWidth / 2, canvas.clientHeight / 2);
+
+        var rectanglePrimitive = createRectangle(rectangle);
+        rectanglePrimitive.appearance.material.uniforms.color = new Color(1.0, 0.0, 0.0, 1.0);
+
+        var primitives = scene.primitives;
+        primitives.add(rectanglePrimitive);
+
+        scene.useDepthPicking = false;
+
+        scene.renderForSpecs();
+
+        var position = scene.pickPosition(windowPosition);
+        expect(position).not.toBeDefined();
+
+        scene.useDepthPicking = true;
+
+        scene.renderForSpecs();
+
+        position = scene.pickPosition(windowPosition);
+        expect(position).toBeDefined();
+    });
+
     it('pickPosition throws without windowPosition', function() {
         expect(function() {
             scene.pickPosition();