minimize the number of batches sent to the GPU

[blockspacer]

The set of primitives to be rendered must be properly sorted by shader to minimize the number of batches sent to the GPU. The algorithm is very similar to those used in 3D engines where objects are sorted by material and textures. Avoiding redundant state changes is also relevant for the UI. This is an important detail that is often overlooked. from https://www.gamasutra.com/view/news/315057/Sponsored_Defining_the_next_generation_of_user_interfaces.php