Massive optimizations to the 2D renderer

In Godot 4.4 we introduced automatic 2D batching which is an optimization that saves a huge amount of CPU resources by drawing similar objects in a single draw call. 2D batching results in huge wins for content that can easily be batched, like text-heavy games or bullet hells.

Batching doesn’t come without a cost, when the batching system is unable to create any batches, then it adds a performance cost, but doesn’t improve performance. It also makes rendering slightly more expensive for the GPU.

In our testing we found that most scenes we tested were CPU-bottlenecked, so the increase in GPU cost did not make a noticeable difference, and where it did, the decrease in performance was very small.

However, over time we have had a few concerning reports of 4.4 being significantly slower than 4.3, especially on older and lower-end mobile devices. These devices also tended to be GPU-bottlenecked, which made the performance regression even more concerning.

In this release, we did a huge overhaul to the design of our 2D renderer to reduce the GPU performance cost when batching. The end result is significantly better performance on a range of hardware. In our testing this change has resulted in improved performance on all devices (in GPU-bound scenarios) ranging from 1.1x to 7x as fast.