Labels with lots of text very slow in Godot 4

[heroofhyla]

Godot version

4.0.3 stable

System information

Windows 10, i5 8600, RTX3060, 64 GB ram

Issue description

In Godot 4, labels with lots of text cause scenes to load extremely slowly, both in the editor and in-game.

I measured a few game starts with different amounts of text in a label:

Text length	Game start time
11323	2.33
22693	7.93
34064	19.69
45431	40.59

In Godot 3, the startup times for all test lengths was almost instantaneous.

The text I used was multiple copies of the license agreement for Google's Roboto font. A "credits" page on a game could easily get well above this length.
Looking at a scatter plot with a best fit, it's pretty clearly increasing at around n^2:

Results are the same whether I'm using the built-in font or a custom font, and results are similar across all renderers. Settings like text wrapping don't seem to affect it either.

Steps to reproduce

Create a scene, add a label to that scene, and fill the label with a large amount of text. Try to launch the game and load that scene.

Minimal reproduction project

Godot3LargeLabel.zip
Godot4LargeLabel.zip

[kleonc]

cc @bruvzg ?

[Calinou]

• Related to Poor performance of 2D Tree View with many items #70869.

Can you check this when using the fallback text server? To do so, compile the editor with the module_text_server_adv_enabled=no module_text_server_fb_enabled=yes SCons options.

[AThousandShips]

Can you compare it to using multiple labels totalling the same amount of text? (Both to pinpoint some details and for workarounds)

[Rindbee]

The size keeps growing to contain all visible text. Increase the height of one line each time.

godot/scene/gui/label.cpp

Lines 275 to 277 in 809a982

	if (autowrap_mode == TextServer::AUTOWRAP_OFF || !clip || overrun_behavior == TextServer::OVERRUN_NO_TRIMMING) {
	update_minimum_size();
	}

godot/scene/gui/label.cpp

Lines 405 to 407 in 809a982

	if (dirty || font_dirty || lines_dirty) {
	_shape();
	}

There seems to be a logic bug in the following code, it's not clear to me why there is a break, it doesn't seem necessary.

godot/scene/gui/label.cpp

Lines 291 to 296 in 809a982

	for (int64_t i = lines_skipped; i < last_line; i++) {
	minsize.height += TS->shaped_text_get_size(lines_rid[i]).y + line_spacing;
	if (minsize.height > (get_size().height - style->get_minimum_size().height + line_spacing)) {
	break;
	}
	}

[MadFlyFish]

I hava a similar problem. It takes a lot of time when add_child a scene with labels.

[Rindbee]

I hava a similar problem. It takes a lot of time when add_child a scene with labels.

This issue does not occur if the initial size is specified to a large value (enough to cover all visible lines of text).

[heroofhyla]

This issue does not occur if the initial size is specified to a large value (enough to cover all visible lines of text).

This is a great catch! I can confirm that it fixes the speed issue. It can be expanded to more complex cases as well. In my case I need the label to be inside a ScrollContainer, and I'm reading the text from files so I don't know exactly how large the label will be.
My scene structure looks like this:

CreditsScene
  ScrollContainer
    Label

I managed to find this solution, expanding off of yours:

1. Set a custom_minimum_size for the label that is much larger than the text you expect to load
2. Load the text from the file into the label
3. Set the custom_minimum_size to 0,0.

Step 1 and 2 go in the Label's _ready function, step 3 goes in the CreditsScene's _ready. If you do it all in the same _ready function you don't get the performance improvement.

The Label's _ready looks like this:

func _ready() -> void:
	custom_minimum_size = Vector2(0,999999)
	text = "\n\n".join(TextFileReader.dir_get_all_text(source_dir))

and the CreditsScene's _ready looks like this:

func _ready():
	$ScrollContainer/Label.custom_minimum_size = Vector2(0,0)

[Calinou]

I can't reproduce this on both 4.0.3 and 4.1.dev 33957ae with the linked MRP for Godot 4 (Linux). The label already appears to be sized to contain all lines of text, so it starts very fast.

[Rindbee]

I can't reproduce this on both 4.0.3 and 4.1.dev 33957ae with the linked MRP for Godot 4 (Linux). The label already appears to be sized to contain all lines of text, so it starts very fast.

Maybe your computer is too powerful. 😄

[Calinou]

Maybe your computer is too powerful. 😄

I mean, I don't even see a difference of 0.1 seconds between master and this PR. While I do have a i9-13900K (which is very fast at single-thread computations), it's not so fast as to make the potential performance difference unnoticeable. IIRC, it's roughly 3-4 times as fast as most Kaby Lake mobile CPUs in terms of single-thread performance. I think something else is going on here.

[Rindbee]

diff --git a/game.tscn b/game.tscn
index 1953d25..9d20ed0 100644
--- a/game.tscn
+++ b/game.tscn
@@ -13,7 +13,7 @@ layout_mode = 0
 offset_left = 16.0
 offset_top = 13.0
 offset_right = 1133.0
-offset_bottom = 623.0
+offset_bottom = 15639.0
 text = "Apache License
                            Version 2.0, January 2004
                         http://www.apache.org/licenses/

I'm guessing the file might have been modified. If it is modified as above, there is no difference.

[Calinou]

I'm guessing the file might have been modified. If it is modified as above, there is no difference.

This was indeed the issue. If I ensure this change isn't made to the scene file, I can reproduce this issue. See #77280 (comment) for results.

Apologies for the false alarm 🙂