Global illumination doesn't update when force drawing a SubViewport if main viewport is disabled

[ydeltastar]

Tested versions

• 4.4.dev
• 4.3.1.rc

System information

Godot v4.4.dev (e3213aa) - Windows 11 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3070 (NVIDIA; 31.0.15.4633)

Issue description

SDFGI takes some frames to converge the global illumination (setting rendering/global_illumination/sdfgi/frames_to_converge).
However, when force drawing a SubViewport like the below example, global illumination doesn't update if the main viewport is disabled.

func _render_subviewport(subviewport: SubViewport, iterations: int = 30,  disable_main = true) -> Image:
	var scene_tree = Engine.get_main_loop() as SceneTree
	var root_viewport = scene_tree.root.get_viewport_rid()
	if disable_main:
		# Disable main viewport so it doesn't redrawn
		RenderingServer.viewport_set_active(root_viewport, false)
	
 	# Render SubViewport
	for i in iterations:
		await RenderingServer.frame_pre_draw
		RenderingServer.viewport_set_update_mode(render.get_viewport_rid(), RenderingServer.VIEWPORT_UPDATE_ONCE)
		RenderingServer.force_draw(true, 1.0 / iterations)
		await RenderingServer.frame_post_draw

	if disable_main:
		# Enable main viewport again
		RenderingServer.viewport_set_active(root_viewport, true)
		await RenderingServer.frame_post_draw # image data doesn't updates correctly without this..

	return subviewport.get_texture().get_image()

Left: expected. Right: result of multiple force_draw(), lighting didn't iterate and it always looks like the first iteration.

It only updates correclty when the main viewport is enabled during force_draw().

But it slows down rendering since force_draw() draws all active viewports although I don't need the main viewport.

Steps to reproduce

• Open the MRP. It contains the test project of the images above.
• Run the project. The left is a realtime SubViewport. The right creates a SubViewport dynamically, force draw multiple times and shows a TextureRect with the resulting image.
• Toggle "Disable main viewport".
• Rendering only looks correct when the main viewport is enabled.

Minimal reproduction project (MRP)

sdfgi-update.zip

[Deltt]

I was about to post this, glad someone else did already. Any potential workarounds that don't slow down rendering time?

[Calinou]

• Related to Add the ability to update/re-render a Viewport manually godot-proposals#1010.