Not even that: SDL just provides a pixel buffer, the application draws everything itself per-pixel. Lite uses a technique I refer to as "cached software rendering" which allows the application code to be written as if it's doing a fullscreen-redrawn when it wants to update, the renderer cache (rencache.c) then works out which regions actually need to be redrawn at the end of the frame and redraws only those. You can call `renderer.show_debug(true)` to show these redraw regions: https://youtu.be/KtL9f6bksDQ?t=50
I wrote a short article detailing the technique here: https://rxi.github.io/200402.html