Why doesn't my custom RichTextEffect do anything?

You must extend RichTextEffect, override _process_custom_fx (CharFXTransform), and add an instance to the RichTextLabel's custom_effects array. The bbcode tag must match the resource's bbcode property name.

How do I read parameters from the BBCode tag?

In _process_custom_fx, char_fx.env is a Dictionary of name=value pairs from the tag. [shake amplitude=10] becomes char_fx.env['amplitude'] = 10. Read and apply per-character.

Can I use a CanvasItem shader?

For label-wide post effects, yes — assign a ShaderMaterial to the RichTextLabel. For per-character effects, RichTextEffect is the correct path because it runs per glyph CharFXTransform.

Fix: Godot 4 RichTextEffect Shader Uniform Not Binding

Quick answer: Extend RichTextEffect, set resource_local_to_scene = true and bbcode = "myfx". Override _process_custom_fx(CharFXTransform). Add an instance to RichTextLabel custom_effects.

Custom [shake] tag in your text does nothing. RichTextEffect resource isn’t in the label’s effects list, or the override method isn’t connected.

The Symptom

BBCode tags wrap text but produce no visual effect. Built-in tags like [shake] work. Custom one doesn’t.

The Fix

# Custom effect resource
extends RichTextEffect
class_name RichTextWobble

@export var bbcode := "wobble"

func _process_custom_fx(char_fx: CharFXTransform) -> bool:
    var amp := float(char_fx.env.get("amplitude", 5))
    var speed := float(char_fx.env.get("speed", 2))
    char_fx.offset.y = sin(char_fx.elapsed_time * speed + char_fx.range.x * 0.3) * amp
    return true

Save as res://wobble_effect.tres (a RichTextWobble resource).

On RichTextLabel:

RichTextLabel:
  bbcode_enabled: true
  custom_effects: [wobble_effect.tres]
  text: "Hello [wobble amplitude=8 speed=4]world[/wobble]!"

The bbcode property on the resource matches the tag name. _process_custom_fx fires per character per frame.

Per-Char Color

func _process_custom_fx(c: CharFXTransform) -> bool:
    c.color = Color.from_hsv(fmod(c.elapsed_time + c.range.x * 0.05, 1.0), 1.0, 1.0)
    return true

Rainbow per-character.

Verifying

Run the scene. Text should wobble. If still static, check: bbcode tag matches resource’s bbcode property; resource is in custom_effects; bbcode_enabled is true.

“Resource with bbcode name. _process_custom_fx. Added to custom_effects. Letters dance.”

Related Issues

For BBCode parsing, see BBCode parsing. For shader uniform runtime, see shader uniform.

Effect resource. bbcode name. Process per char.