HUD post-processing in Godot

Question

I have a project in Godot that renders billboarded quads on top of enemies. The quads(meshinstances) are children nodes of the enemy nodes. I want to render just the quads to a viewport for post-processing, but the quads need to have the same position on screen that the enemies have (like a target reticle). How can I apply a shader effect to the billboards only and not to the rest of the scene?

Answer 1

The Camera has a cull_mask property that lets you filter which layers it will see. And VisualInstances (such as MeshInstances) have a layers property that lets you specify to which layers they belong (by default they all belong to the first layer).

You can configure the layers names in Project Settings -> General -> Layer Names -> 3d Render. Do not confuse them with 3d Physics.

Thus, you can give a different layer to those quad MeshInstance you want, and then setup a new Viewport with a new Camera as child (make sure it is current) with a cull_mask that will only render that layer. That way only those MeshInstance will be rendered on that Viewport.

You probably want to to keep the properties of the Camera in sync with the Camera on main Viewport (not only its global_transform, but also fov or any other property you might change). You can archive this by copying its properties on _process of a script attached to the Camera which is inside the new Viewport.