Labels/billboards on terrain and depthTestAgainstTerrain

When labels/billboards are clamped to terrain, they require depthTestAgainstTerrain to be false so they do not sink into terrain. However, this allows 3D models and extruded geometries, for example, to come through terrain.

@bagnell and I have brainstormed a few ideas like using an extra depth buffer or stenciling. We’re hoping for something simpler though.

[emackey]

I like the “whole entity” idea. I’ve encountered more than one project where they want an all-or-nothing test for visibility of the entity (point, billboard, and label, together). If the entity’s single location is exposed to the camera, then the point+billboard+label graphics should be visible in their entirety, unfettered by depth-buffering. But if the entity is obscured, even just hidden behind a small hill, then the point+billboard+label graphics are turned off completely. At no time is a partial label or partial marker symbol (billboard) ever shown to the user, nor a marker without a label or vice-versa. Essentially, the 2D elements don’t need to participate in the 3D scene at all, beyond yes-or-no knowledge of whether the object they represent is visible within the scene, and its screen-space location.

Points, billboards, and labels in such a system could even be moved to a separate render pass where FXAA was not applied to them, which would be an added win.

[gooin]

@thw0rted Awesome！Thank you.