I've been looking more into the Godot GUI lags on
tree change issue with the help of a friend in Godot
4.2.2. and we've managed to track down the root
cause to the RichTextLabel
taking a
long time when it is first drawn.
RichTextLabel
uses another class to
draw text called TextParagraph
.
Consider the example below, where
TextParagraph
is used directly:
@toolclass_name CachedTextLabel
extends Control
var text: String:
@export_multiline set(value):
if text != value:
= value
text
var font := get_theme_default_font()
var font_size := get_theme_default_font_size()
= TextParagraph.new()
paragraph add_string(text, font, font_size)
paragraph.
queue_redraw()
var paragraph: TextParagraph
func _draw() -> void:
var start := Time.get_ticks_msec()
= size.x
paragraph.width = TextServer.BREAK_MANDATORY | TextServer.BREAK_WORD_BOUND
paragraph.break_flags = TextServer.JUSTIFICATION_NONE
paragraph.justification_flags = HORIZONTAL_ALIGNMENT_LEFT
paragraph.alignment draw(get_canvas_item(), Vector2.ZERO)
paragraph.var end := Time.get_ticks_msec()
print("_draw: ", end - start, "ms")
Normally, the draw performance is fine. However, also consider that we want to render the following text (like I want to do in no signal):
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Under these conditions, the first draw call takes
about 100ms on my machine to run (and about 300ms)
on my laptop. However, subsequent draw calls take
only 1ms. It seems like TextParagraph
is lazily loading in some data when the first draw
call happens.
We can proactively trigger whatever it is that
TextParagraph
would otherwise do before
the first draw call...
func _ready() -> void:
get_size() paragraph.
...and this fixes the lag that happens on the first draw call.
So, it looks like the performance problem
isn't an issue with tree changes, but
rather something that the RichTextLabel
does when rendered for the first time.