标签：#unityui

Why Is Overdraw Particularly Important in WebGL? When optimizing a Unity WebGL application, developers often focus on polygon count, draw calls, texture size, and shader complexity. But there is another performance problem that can quietly become expensive: UI overdraw . A UI may look simple to the player while the GPU is actually rendering the same pixels several times. A typical game interface might contain: A full-screen background Transparent panels Multiple decorative images Buttons Shadows Icons Text Semi-transparent overlays Popups Individually, these elements may seem harmless. When stacked together, however, they can significantly increase the number of pixels the GPU needs to process. Unity identifies overlapping transparent UI, sprites, and particles as common contributors to overdraw. So, is UI overdraw really killing your WebGL performance? Let's understand when it matters and how to reduce it. What Exactly Is UI Overdraw? Overdraw occurs when the same screen pixel is rendered multiple times during a frame. Imagine a 1920×1080 WebGL game with this UI: Full-screen background ↓ Transparent dark overlay ↓ Semi-transparent panel ↓ Panel decoration ↓ Button background ↓ Button icon ↓ Button text A pixel covered by all these elements may be processed repeatedly. Conceptually: GPU ↓ ┌──────────────┐ │ Background │ ← 1 │ Overlay │ ← 2 │ Panel │ ← 3 │ Decoration │ ← 4 │ Button │ ← 5 │ Icon │ ← 6 │ Text │ ← 7 └──────────────┘ Same pixel processed multiple times This is particularly relevant when your UI contains large transparent elements covering substantial portions of the screen. Unity's graphics documentation specifically recommends identifying and reducing overdraw when fill rate becomes a GPU limitation. Why Is Overdraw Particularly Important in WebGL? WebGL runs inside a browser, so performance has additional constraints compared with a native desktop application. If your application is GPU-bound, rendering unnecessary pixels means the GPU has more work to