1 Batching Instances
Instructing the GPU to draw something takes time. Feeding it the data to do so,
including the mesh and material properties, takes time as well. We already know of
two ways to decrease the amount of draw calls, which are static and dynamic
batching.
Unity can merge the meshes of static objects into a larger static mesh, which reduces
draw calls. Only objects that use the same material can be combined in this way. This
comes at the cost of having to store more mesh data. When dynamic batching is
enabled, Unity does the same thing at runtime for dynamic objects that are in view.
This only works for small meshes, otherwise the overhead becomes too great.
There is yet another way to combine draw calls. It is know as GPU instancing or
geometry instancing. Like dynamic batching, this is done at runtime for visible
objects. The idea is that the GPU is told to render the same mesh multiple times in
one go. So it cannot combine di!erent meshes or materials, but it's not restricted to
small meshes. We're going to try out this approach.
1.1 Many Spheres
To test GPU instancing, we need to render the same mesh many times. Let's create a
simple sphere prefab for this, which uses our white material.
White sphere prefab.
To instantiate this sphere, create a test component which spawns a prefab many
times and positions it randomly inside a spherical area. Make the spheres children of
the instantiator so the editor's hierarchy window doesn't have to struggle with
displaying thousands of instances.
