When you are building a game world that needs to feel alive - dense forests, sprawling cities, battlefields with hundreds of units - you hit a fundamental rendering bottleneck long before your polygon count becomes the problem. The bottleneck is draw calls.
Every time Unity tells the GPU to render an object, it issues a draw call. Each draw call has CPU overhead: setting up the material, binding textures, configuring the render state. On desktop hardware, you can get away with a few thousand draw calls per frame. On mobile, you often need to stay under 200 to maintain a stable 60 FPS.
This is the challenge we faced when engineering the environment systems for Domi Online - an MMORPG with dense, interactive forests where every single tree can be chopped down. We needed to render 10,000+ trees across the visible world with minimal draw calls on mid-range hardware, while still allowing players to interact with individual objects.
In this article, we will walk through the GPU instancing techniques we use to solve this problem, covering the SRP Batcher, manual GPU instancing, LOD strategies, and the interactive-object swap pattern that makes dense worlds both beautiful and functional.
Understanding the Draw Call Problem
