Using marker as occluder

Hi, whilst pondering over how to implement some "photorealism" into Vuforia AR I came up with following simple shader idea. As basis there would be one marker in the middle of a paper plus a 3D object which is partly "below" the marker. In test implementation I'm about to try this would be a rotating cube which is positioned at (0, 0, 0). In this case you would want to occlude parts of the object that are under the marker.

To implement this I was thinking about following shaders.

uniform mat4 uModelViewMatrix; uniform mat4 uProjectionMatrix; attribute vec3 aPosition; varying vec4 vPosition; void main() {   vPosition = uModelViewMatrix * vec4(aPosition, 1.0);   gl_Position = uProjectionMatrix * vPosition; }

varying vec4 vPosition; void main() {   if (vPosition.z < 0.0) {     discard;   } else {     // Render pixel with actual color.   } }

I still have to try this out but leaving the idea here for comments and future reference.