Vertex colors are assigned incorrectly in quadrilaterals drawn using CommandPrimitive

[Lielay9]

Tested versions

Master as of writing: v4.4.dev.custom_build [76a1359]
Regression after #92797 (bisected)

System information

Godot v4.4.dev (a657ea4) - Windows 10.0.22631 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 4090 (NVIDIA; 31.0.15.3699) - AMD Ryzen 9 7950X 16-Core Processor (32 Threads)

Issue description

Quadrilaterals drawn using CommandPrimitive (RenderingServer.canvas_item_add_primitive(), antialiasing etc.) assign the provided vertex colors incorrectly after #92797 in the RD-renderers. More specifically, the second constructed triangle (top left, bottom right, bottom left in the first image) uses the colors indexed at 0, 1 and 2, when it should use 0, 2 and 3.

func _draw() -> void:
	var uvs: PackedVector2Array = [Vector2.ZERO, Vector2.RIGHT, Vector2.ONE, Vector2.DOWN]
	var colors: PackedColorArray = [Color.WHITE, Color.RED, Color.GREEN, Color.BLUE]
	var points: PackedVector2Array = uvs.duplicate()
	for i: int in points.size():
		points[i] *= 500
		points[i] += Vector2(50, 50)
	draw_primitive(points, colors, uvs)

Incorrect antialiasing of line (drawn with scale 10 to blow out the feather size):

Compatibility for reference:

Steps to reproduce

↕

Minimal reproduction project (MRP)

primitivevertexcolors.zip

[stuartcarnie]

Reproduced it – thanks for the MRP!

Fixed in #97340: