Using Clutter color paint node with cogl primititives ignores depth test

[Reza Ghassemi <reza robin1 gmail com>]

Hi,

We wanted a color gradient actor so we added a new implementation of ClutterContent.  In its paint_content routine, it creates a ClutterColorNode, then creates a CoglPrimitive of a triangle strip with the desired colors at the vertices and adds the primitive to the paint node.  

This works fine in most cases.  However when cogl_set_depth_test_enabled is set to true (yes, I know this is the deprecated call now, but it was written with an older version of cogl) and other actors are in front of the actor with the gradient, the gradient content shows on top ignoring the depth.  Note that I am using the COGL_EXPERIMENTAL_API here.

Does anyone know why this is happening or what I'm doing wrong or how to fix this problem?  

Thanks,

Reza