ui-imgui

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

Analyze — Determine script type needed (EditorWindow, Editor, PropertyDrawer, etc.)
Search — Find existing editor scripts to match patterns
Follow project patterns — Match folder structure and naming
Create script — Use appropriate base class and attributes
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:

csharp

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

Vertical grouping:

csharp

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

Scroll view:

csharp

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

Foldout section:

csharp

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

Common Patterns

Button with action:

csharp

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

Property field with label:

csharp

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

Object reference field:

csharp

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

Disabled group:

csharp

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.

ui-imgui

NPX Install

Tags

SKILL.md Content

When to Use This Skill

Scope

Conventions

Workflow

Script Structure

EditorWindow

Custom Editor

PropertyDrawer

Key Rules

Layout Basics

Common Patterns

Best Practices