Add a RenderingServer method to quickly clone a CanvasItem

[gokiburikin]

Context

I'm making a game where all the graphics are rendered using RenderingServer.canvas_item_add_multiline, RenderingServer.canvas_item_add_rect, and similar calls.

It looks like this.

What I'm doing

I make a CanvasItem for each entity so that I can don't have to call of the draw_* commands every frame for each of them. This also allows me to change their colours and transforms, but the "initial draw" where I add commands to the CanvasItem is being "wastefully" done each and every time I make a new entity resulting in the exact same CanvasItem "state" before modulate and transforms are applied.

These CanvasItems are prepared with an array of lines to draw (with draw_multiline) and every time I make a new bullet, enemy, or particle I call the same series of draw commands on it to get it to its "base" state.

What I want to do

If I could just "clone" the state of an existing CanvasItem or alternatively tell Godot to render a CanvasItem with two different transforms and modulates (like MultiMesh seems to do) I assume there would be a performance gain.

Why I thought about this solution

I originally was using Polyline but it does not handle sharp turns well so I moved to Multilines. Problem with Multilines is that you don't get corner shaping. My original solution was to call draw_circle at each point and that looks great, but draw_circle is the slowest thing in the known universe so it brought my game to a crawl.

Line Points Visual Comparison

In response I made a little benchmark for testing alternatives to draw_circle that still gave me good results at the scale I was using (very small) and at that size draw_rect is mostly good enough. It turned out that a significant amount of time is spent simply calling the draw_circle function to prepare the CanvasItem; not actually doing the drawing.

Thoughts

Granted, if you're not clearing and re-drawing the CanvasItem each update then you only incur this cost the first time (the intended way to use CanvasItems I imagine), but what this does mean is that moments in the game where there is a lot of instantiation (spawning in a bunch of enemies or projectiles on one frame for example) I perform these functions that result in the exact same commands on each separate CanvasItem apart from whatever unique ids have to be allocated.

Technically I could have a pool of CanvasItems with each shape so I can just pluck one from the pool and if this doesn't pan out that's probably what I will do.

Functionally what I hoped I could do is set up "reference" CanvasItems to call something like RenderingServer.canvas_item_copy( target_canvas_item:RID, reference_canvas_item:RID ) on and have the same commands be quickly copied over to the new CanvasItem without doing all the calculations. After these draw_* commands all I ever want to do is set their modulate and transforms anyway which doesn't require calling the commands again.

It's possible of course that I just don't know how to use MultiMesh through the RenderingServer (I don't know how you'd pass it a CanvasItem as the source mesh) and it is exactly what I'm looking for.

There may even already be code to do this since Nodes can be copy pasted, but I don't know how to search the source code for that.