Merge pull request #4930 from AnalyticalGraphicsInc/ground-primitive-no-frag-depth

Enable GroundPrimitives to render without the fragment depth extension.

Author: mramato

CHANGES.md

@@ -1,6 +1,10 @@
 Change Log
 ==========
 
+### 1.31 - 2017-03-01
+
+* Enable rendering `GroundPrimitives` on hardware without the `EXT_frag_depth` extension; however, this could cause artifacts for certain viewing angles.
+
 ### 1.30 - 2017-02-01
 
 * Deprecated

Source/Scene/GroundPrimitive.js

@@ -84,9 +84,8 @@ define([
      * is supported at this time.
      * </p>
      * <p>
-     * Because of the cutting edge nature of this feature in WebGL, it requires the EXT_frag_depth extension, which is currently only supported in Chrome,
-     * Firefox, Edge, and Safari 10. It's not yet supported in iOS 10. Android support varies by hardware and IE11 will most likely never support
-     * it. You can use webglreport.com to verify support for your hardware.
+     * For correct rendering, this feature requires the EXT_frag_depth WebGL extension. For hardware that do not support this extension, there
+     * will be rendering artifacts for some viewing angles.
      * </p>
      * <p>
      * Valid geometries are {@link CircleGeometry}, {@link CorridorGeometry}, {@link EllipseGeometry}, {@link PolygonGeometry}, and {@link RectangleGeometry}.
@@ -400,7 +399,7 @@ define([
      * @returns {Boolean} <code>true</code> if GroundPrimitives are supported; otherwise, returns <code>false</code>
      */
     GroundPrimitive.isSupported = function(scene) {
-        return scene.context.fragmentDepth && scene.context.stencilBuffer;
+        return scene.context.stencilBuffer;
     };
 
     GroundPrimitive._defaultMaxTerrainHeight = 9000.0;
@@ -1032,8 +1031,7 @@ define([
      * @exception {DeveloperError} Not all of the geometry instances have the same color attribute.
      */
     GroundPrimitive.prototype.update = function(frameState) {
-        var context = frameState.context;
-        if (!context.fragmentDepth || !this.show || (!defined(this._primitive) && !defined(this.geometryInstances))) {
+        if (!this.show || (!defined(this._primitive) && !defined(this.geometryInstances))) {
             return;
         }
 

Source/Shaders/ShadowVolumeFS.glsl

@@ -1,12 +1,16 @@
+#ifdef GL_EXT_frag_depth
 #extension GL_EXT_frag_depth : enable
+#endif
 
 // emulated noperspective
 varying float v_WindowZ;
 varying vec4 v_color;
 
 void writeDepthClampedToFarPlane()
 {
+#ifdef GL_EXT_frag_depth
     gl_FragDepthEXT = min(v_WindowZ * gl_FragCoord.w, 1.0);
+#endif
 }
 
 void main(void)