Godot Compute-Shader Image to TextureRect Example

Many resources about how to use compute shaders in Godot 4.6 are insufficient if what you want to do is have compute shaders output/modify something on the GPU every frame (or physics frame) and have that same resource available to regular nodes or the main renderer.

For example, the heightmap example uses a local rendering device and downloads the texture to the CPU just to reupload that texture to the GPU again.

This is fine if it happens occasionally. It is not fine if we are talking about a simulation that modifies large images or particle data that we want to access in our normal rendering outside of the RenderingDevice API.

The project I have provided here contains a toy example that shows how to do this:

• Uses RenderingServer.get_rendering_device() so that Resources allocated can be accessed by nodes
• Uses Texture2DRD to bind a texture created on the RenderingDevice to a standard TextureRect node
• Has example code that handles a change in width/height of the simulation texture in a deferred manner
• Shows the correct Usage Bits for the texture such that Sampling (usage as texture via Texture2DRD or directly in a uniform sampler2D) and Image Load/Store are possible (Storage Bit)
• Shows how to use Push Constants for Shader data that changes frequently
• Shows how to use image2D to write to an image in a compute shader

This toy example queues a compute shader dispatch in _physics_process such that it executes a stable number of times per second, which is what you usually want for simulations. It would work the same way if you want to run it in _process instead. A push constant is set alternating between 0 and 1 which the shader reacts to by either outputting a horizontal or vertical gradient.

There is no submit() or sync() because this is done automatically behind the scenes for the main rendering device.

The reason all the variables are talking about Sand is because I was going to use this as a baseline to implement a sand simulation, but when I had the basic template running I thought that it would be valuable to share with anyone interested in learning about compute shaders in Godot.