ui-imgui

name	ui-imgui
description	Unity IMGUI (Immediate Mode GUI) expert for legacy editor tools using OnGUI/immediate mode. Generates and modifies IMGUI EditorWindows, custom Inspectors, PropertyDrawers, and scripts with IMGUI code (OnGUI, OnInspectorGUI). Use when maintaining existing IMGUI editor code or when user explicitly requests IMGUI/OnGUI.
allowed-tools	["Read","Write","Edit","Glob","Grep"]

Before proceeding: If the user is asking about creating a new editor window, custom inspector, or PropertyDrawer without explicitly mentioning IMGUI/OnGUI, recommend using UI Toolkit (CreateGUI) instead, as it's the modern approach. Only proceed with IMGUI if:

• User is modifying existing IMGUI code
• User explicitly requests IMGUI/immediate mode
• The project exclusively uses IMGUI for editor tools

When activated, read the reference files:

• references/templates.md — EditorWindow, Inspector, PropertyDrawer templates
• references/gui-elements.md — GUI elements, layout groups, styling

When to Use This Skill

IMPORTANT: This skill is for legacy IMGUI code only. Use this skill when:

• User is maintaining/updating existing IMGUI editor code (files with OnGUI(), OnInspectorGUI())
• User explicitly requests IMGUI/immediate mode GUI
• Project exclusively uses IMGUI for all editor tools

Do NOT use this skill for:

• New editor windows (use UI Toolkit with CreateGUI() instead)
• New custom inspectors (use UI Toolkit instead)
• Requests that don't explicitly mention IMGUI or OnGUI

Legacy IMGUI is used for:

• Editor windows — EditorWindow classes with OnGUI()
• Custom inspectors — Editor, PropertyDrawer classes with OnInspectorGUI()
• Debug overlays — OnGUI() in MonoBehaviour (runtime)

IMGUI is not for runtime game UI — use UI Toolkit or uGUI instead.

Scope

Generate only what is requested (for legacy IMGUI code):

Request	Output	Note
Editor window (IMGUI/OnGUI)	EditorWindow with OnGUI()	Only if explicitly IMGUI
Custom inspector (IMGUI)	Editor with OnInspectorGUI()	Only if explicitly IMGUI
Property drawer (IMGUI)	PropertyDrawer with OnGUI()	Only if explicitly IMGUI
Debug overlay	MonoBehaviour with OnGUI()	Runtime debugging
Update existing IMGUI script	Modify existing OnGUI code	Always appropriate

Clarify if ambiguous:

• "inspector" → Custom Editor for a specific type, or PropertyDrawer? Also ask: Should this use UI Toolkit (modern) or IMGUI (legacy)?
• "editor window" → First ask: Should this use UI Toolkit (modern/CreateGUI) or IMGUI (legacy/OnGUI)?
• "tool window" → EditorWindow with what functionality? Which UI system?

Conventions

Follow project patterns first. Search existing editor scripts before applying defaults.

Type	Convention	Good	Bad
Script names	PascalCase	MyToolWindow.cs	my-tool-window.cs
EditorWindow	[Name]Window.cs	LevelEditorWindow.cs	LevelEditor.cs
Custom Editor	[Type]Editor.cs	EnemyEditor.cs	EnemyInspector.cs
PropertyDrawer	[Type]Drawer.cs	RangeDrawer.cs	RangePropertyDrawer.cs
Location	Editor folder	Assets/Editor/	Assets/Scripts/

Editor folder is required — Scripts using UnityEditor namespace must be in an Editor folder or they will fail to build.

Workflow

1. Analyze — Determine script type needed (EditorWindow, Editor, PropertyDrawer, etc.)
2. Search — Find existing editor scripts to match patterns
3. Follow project patterns — Match folder structure and naming
4. Create script — Use appropriate base class and attributes
5. Implement OnGUI — Build the interface with layout groups

Script Structure

EditorWindow

[MenuItem attribute] → adds to menu
ShowWindow() static method → opens window
OnGUI() → draws interface
OnEnable/OnDisable → initialization/cleanup

Custom Editor

[CustomEditor attribute] → targets component type
OnInspectorGUI() → draws inspector
OnEnable() → cache SerializedProperties
serializedObject.Update/ApplyModifiedProperties → undo support

PropertyDrawer

[CustomPropertyDrawer attribute] → targets type or attribute
OnGUI(Rect, SerializedProperty, GUIContent) → draws property
GetPropertyHeight() → custom height if needed

Key Rules

• Cache GUIStyle objects — never create new GUIStyle in OnGUI (causes memory allocation every frame)
• Use SerializedProperty — for proper undo/redo support in inspectors
• Call ApplyModifiedProperties() — after any serialized object changes
• Use EditorGUILayout — for editor scripts (auto-layout)
• Use GUILayout — for runtime OnGUI
• Begin/End pairs — always match BeginHorizontal with EndHorizontal, etc.
• Editor folder required — scripts fail to build if not in Editor folder

Layout Basics

Horizontal grouping:

EditorGUILayout.BeginHorizontal();
// elements appear side by side
EditorGUILayout.EndHorizontal();

Vertical grouping:

EditorGUILayout.BeginVertical("box");
// elements appear stacked, with box style
EditorGUILayout.EndVertical();

Scroll view:

scrollPos = EditorGUILayout.BeginScrollView(scrollPos);
// scrollable content
EditorGUILayout.EndScrollView();

Foldout section:

showSection = EditorGUILayout.Foldout(showSection, "Section Name");
if (showSection)
{
    EditorGUI.indentLevel++;
    // section content
    EditorGUI.indentLevel--;
}

Common Patterns

Button with action:

if (GUILayout.Button("Do Something"))
{
    // action here
}

Property field with label:

EditorGUILayout.PropertyField(myProperty, new GUIContent("Label"));

Object reference field:

myObject = (MyType)EditorGUILayout.ObjectField("Label", myObject, typeof(MyType), true);

Disabled group:

EditorGUI.BeginDisabledGroup(condition);
// disabled elements
EditorGUI.EndDisabledGroup();

Best Practices

• Use SerializedObject and SerializedProperty for undo support
• Cache property references in OnEnable()
• Use EditorUtility.SetDirty() only for non-serialized changes
• Use Undo.RecordObject() before modifying objects directly
• Use EditorStyles for consistent appearance
• Use GUILayout.FlexibleSpace() to push elements apart

See references/templates.md for complete script templates. See references/gui-elements.md for full element reference.