Support tiling AtlasTexture in TextureRect

[kleonc]

Fixes #113691.

Adds support for tiling an AtlasTexture assigned to a TextureRect by drawing it as a nine patch, which already supports tiling a texture region.

Before v4.6.dev6.official [dec5a37]	After this PR

[arkology]

In basic situation (without margins and atlas nesting) works great.

I don't understand how atlas margins supposed to work in this situation, so I just recorded a video.

Godot_v4.6-dev6_win64_kX5jEjY60q.mp4

[kleonc]

I don't understand how atlas margins supposed to work in this situation,

If properly supported, the whole atlas texture should be tiled treated as a single "unit", including the margins. Like this:

Godot_v4.5.1-stable_win64_UYYpo76D5F.mp4

Here's script drawing the above (each "tile" is a separate quad):

@tool
extends Control

@export var texture: AtlasTexture

func _process(delta: float) -> void:
	queue_redraw()

func _draw() -> void:
	var texture_size := texture.get_size()
	var drawable_area := Rect2(Vector2.ZERO, size)
	var repeat_count: Vector2i = (size / texture_size).ceil()
	for y in repeat_count.y:
		for x in repeat_count.x:
			var cell_coords := Vector2(x, y)
			var cell_rect_unclamped := Rect2(cell_coords * texture_size, texture_size)
			var cell_rect_clamped := cell_rect_unclamped.intersection(drawable_area)
			var src_rect := Rect2(Vector2.ZERO, cell_rect_clamped.size)
			draw_texture_rect_region(texture, cell_rect_clamped, src_rect)

so I just recorded a video.

Which clearly shows that margins are nor handled "as expected".

To handle the margins properly the tiling would need to be drawn either:

• As many separate quads.
• As a single quad, but the margins-area would need to be discarded in the fragment shader. This would require modifying the canvas shader for supporting it. But for big margins this would be inefficient (normally for AtlasTextures the margins part is not rendered at all, it's included in the texture size only logically; only the region part is actually rendered / runs the shader).

So for now I'll only add a note that tiling an AtlasTextures with margins is not supported.

In basic situation (without margins and atlas nesting) works great.

Regarding atlas nesting, note that any number of nested atlas textures (assuming no cyclic dependency, which would likely lead to crashing as it's not being prevented / checked against) can be simplified to a single combined region+margin (nesting can't result in holes etc.), aka it's equivalent to considering a single AtlasTexture. For supporting nesting only such cumulated final region needs to be calculated. Updated the PR accordingly (so nesting with no margins should work just fine).

[arkology]

As we started deeper discussion about margins. I have 2 PRs, #101000 and #101024, where I broke my mind and gave up because of margins😄 Not sure I'll ever finish them.

[Repiteo]

Thanks!