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:
@tool
class_name CachedTextLabel
extends Control
@export_multiline var text: String:
set(value):
if text != value:
text = value
var font := get_theme_default_font()
var font_size := get_theme_default_font_size()
paragraph = TextParagraph.new()
paragraph.add_string(text, font, font_size)
queue_redraw()
var paragraph: TextParagraph
func _draw() -> void:
var start := Time.get_ticks_msec()
paragraph.width = size.x
paragraph.break_flags = TextServer.BREAK_MANDATORY | TextServer.BREAK_WORD_BOUND
paragraph.justification_flags = TextServer.JUSTIFICATION_NONE
paragraph.alignment = HORIZONTAL_ALIGNMENT_LEFT
paragraph.draw(get_canvas_item(), Vector2.ZERO)
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:
paragraph.get_size()...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.