RENDER_BATCHING

A variable controlling whether the 2D render API is compatible or efficient.

This variable can be set to the following values:

• "0" - Don't use batching to make rendering more efficient.
• "1" - Use batching, but might cause problems if app makes its own direct OpenGL calls.

Up to SDL 2.0.9, the render API would draw immediately when requested. Now

it batches up draw requests and sends them all to the GPU only when forced

to (during SDL_RenderPresent, when changing render targets, by updating a

texture that the batch needs, etc). This is significantly more efficient,

but it can cause problems for apps that expect to render on top of the

render API's output. As such, SDL will disable batching if a specific

render backend is requested (since this might indicate that the app is

planning to use the underlying graphics API directly). This hint can

be used to explicitly request batching in this instance. It is a contract

that you will either never use the underlying graphics API directly, or

if you do, you will call SDL_RenderFlush() before you do so any current

batch goes to the GPU before your work begins. Not following this contract

will result in undefined behavior.