Comparing UI Systems

Unity offers three different UI systems, each suited for different tasks. Choosing the right system depends on your target platform and workflows.

1. UI Toolkit (Modern Standard)

• Inspired by web technologies (HTML/CSS).
• Uses UXML for structure and USS for styling.
• Features a visual UI Builder editor.
• Highly optimized, supports stylesheet reuse, and is the recommended system for new runtime game UIs and editor extensions.

2. Unity UI (UGUI)

• The legacy GameObject-based system.
• Uses Components like Canvas, RectTransform, Image, and Button.
• Positioned in 3D or 2D scene space.
• Highly visual inside the Scene view, but can suffer from performance issues on complex layouts due to Canvas rebuilding.

3. Immediate Mode GUI (IMGUI)

• An old, code-driven UI system.
• Formulated entirely in the OnGUI() script method.
• Re-renders everything every frame (immediate mode).
• Not suitable for game interfaces, but still useful for writing quick, custom editor tools.

TL;DR

• UI Toolkit: Uses HTML/CSS concepts (UXML/USS) and is recommended for new projects.
• UGUI: GameObject-based (Canvas/RectTransform); widely used in older projects.
• IMGUI: Code-driven, immediate mode; used primarily for simple editor tools.