To draw geometry on the screen, Unity issues draw calls to the graphics API. A draw call tells the graphics API what to draw and how to draw it. Each draw call contains all the information the graphics API needs to draw on the screen, such as information about textures, shaders, and buffers. Draw calls can be resource intensive, but often the preparation for a draw call is more resource intensive than the draw call itself.
To prepare for a draw call, the CPU sets up resources and changes internal settings on the GPU. These settings are collectively called the render state. Changes to the render state, such as switching to a different material, are the most resource-intensive operations the graphics API performs.
Because render-state changes are resource intensive, it is important to optimize them. The main way to optimize render-state changes is to reduce the number of them. There are two ways to do this:
Optimizing draw calls and render-state changes has a number of benefits for your application. Mainly, it improves frame times, but it also:
There are several methods you can use in Unity to optimize and reduce draw calls and render-state changes. Some methods are more suited for certain scenes than others. The following methods are available in Unity:
position
and normal
.You can use multiple draw call optimization methods in the same scene but be aware that Unity prioritizes draw call optimization methods in a particular order. If you mark a GameObject to use more than one draw call optimization method, Unity uses the highest priority method. The only exception to this is the SRP Batcher. When you use the SRP Batcher, Unity also supports static batching for GameObjects that are SRP Batcher compatible. Unity prioritizes draw call optimizations in the following order:
If you mark a GameObject for static batching and Unity successfully batches it, Unity disables GPU instancing for that GameObject, even if the renderer uses an instancing shader. When this happens, the Inspector window displays a warning message that suggests that you disable static batching. Similarly, if Unity can use GPU instancing for a mesh, Unity disables dynamic batching for that mesh.