FS#5748 : Fix Skipping Audio in Simulator on OS X (caused by excessive surface blitting in SDL)

Status Closed
Percent Complete
100%
Task Type Patches
Category User Interface → Simulator
Assigned To

safetydan
Operating System All players
Severity Critical
Priority Very Low
Reported Version
Due in Version Undecided
Due Date Undecided
Votes
Private

Attached to Project: Rockbox
Opened by ezephir - 2006-07-31

FS#5748 - Fix Skipping Audio in Simulator on OS X (caused by excessive surface blitting in SDL)

The SDL simulator on OS X when compiled skips while playing audio. The message reported is:

sdl_audio_callback: No Data.

Upon investigation, this behaviour only occurs when the simulator window was visible. Upon closer investigation, the Simulator draws to the screen twice, once with SDL_UpdateRect() and again with SDL_Flip(). According to the SDL Documentation (www.libsdl.org/cgi/docwiki.cgi/SDL_5fFlip), SDL_Flip is equivalent to updating the whole screen with SDL_UpdateRect().

When hardware aceleration is available, SDL_UpdateRect() AFAIK is bad when double buffering is used because the backbuffer is a frame behind the current LCD display. If only a region of it is updated, as the original code did, the output will contain a mixture of the new LCD and the one a frame before it.

Because of the incorrect behavior when the program is double buffered, and the redundancy that keeps the OS X version of the simulator, I removed the call to SDL_UpdateRect(). The program output seems to still be correct, and the OS X version no longer skips on any of the computers I’ve tested on.