Fix for 3D Blending. (#440)

* Minimal Fix for 3D Blending.

* Remove culling on layer

src/layers/VolumeLayer/VolumeLayer.js

@@ -1,4 +1,5 @@
 import { CompositeLayer, COORDINATE_SYSTEM } from '@deck.gl/core';
+import GL from '@luma.gl/constants';
 import { TextLayer } from '@deck.gl/layers';
 import { Matrix4 } from 'math.gl';
 import XR3DLayer from '../XR3DLayer';
@@ -168,6 +169,13 @@ const VolumeLayer = class extends CompositeLayer {
       channelData: { data, width, height, depth },
       id: `XR3DLayer-${0}-${height}-${width}-${0}-${resolution}-${id}`,
       physicalSizeScalingMatrix,
+      parameters: {
+        [GL.CULL_FACE]: true,
+        [GL.CULL_FACE_MODE]: GL.FRONT,
+        [GL.DEPTH_TEST]: false,
+        blendFunc: [GL.SRC_ALPHA, GL.ONE],
+        blend: true
+      },
       resolutionMatrix,
       dtype
     });

src/layers/XR3DLayer/XR3DLayer.js

@@ -135,11 +135,6 @@ const XR3DLayer = class extends Layer {
     this.setState({
       model: this._getModel(gl)
     });
-    // Needed to only render the back polygons.
-    setParameters(gl, {
-      [GL.CULL_FACE]: true,
-      [GL.CULL_FACE_MODE]: GL.FRONT
-    });
     // This tells WebGL how to read row data from the texture.  For example, the default here is 4 (i.e for RGBA, one byte per channel) so
     // each row of data is expected to be a multiple of 4.  This setting (i.e 1) allows us to have non-multiple-of-4 row sizes.  For example, for 2 byte (16 bit data),
     // we could use 2 as the value and it would still work, but 1 also works fine (and is more flexible for 8 bit - 1 byte - textures as well).