Surface2D

Surface2D is a Godot 4 plugin adding polygonal surfaces on which decals can drawn.

Installation

1. Copy addons/surface_2d folder into addons directory of your project.

2. Enable this plugin in Project > Project Settings... > Plugins.

Usage

1. Add a new Surface2D node to the scene.

2. Draw the shape of your surface by adding points in the scene view.

3. Choose a rendering layer to use for drawing decals (by default it is layer 2).

4. Set cull_mask of the surface and visibility_layer of the canvas item to that layer.

5. Now when this canvas item intersects with the surface it should be drawn on it.

Tips

visibility_layer and cull_mask of the surface itself should NOT overlap (or the surface will try to draw itself on itself which normally causes a tsunami of errors).

It is a good practice to name rendering layers, similarly to physics layers, in Project Settings.

If a node you want to draw has a parent of CanvasItem type, then that parent has to also have an appropriate visibility_layer set. In other words, visibility_layer propagates down the tree, similarly to how transforms do.

For understanding how mask culling and visibility layers work I recommend this excellent tutorial. Surface2D uses mechanisms mentioned there.