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Bug 5097

Summary: Emscripten: connecting and disconnecting real-joysticks can close virtual joysticks
Product: SDL Reporter: David Ludwig <dll>
Component: joystickAssignee: Sam Lantinga <slouken>
Status: NEW --- QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: dll
Version: HG 2.0   
Hardware: Other   
OS: Other   
Attachments: Fix #1: use SDL_GetNextJoystickInstanceID() for alloc'ing joystick-ids in Emscripten joystick backend

Description David Ludwig 2020-04-18 15:52:40 UTC 
SDL2's Emscripten joystick backend appears to be allocating SDL_JoystickIDs using its own, private, integer counter, rather than through SDL_GetNextJoystickInstanceID().  This can have harmful effects if and when a virtual joystick is attached (using functionality new to SDL 2.0.13+).  For example, when connecting and disconnecting real game-controller hardware, Emscripten's joystick backend can assign an SDL_Joystick a SDL_JoystickID that is being used by an active virtual-joystick (which uses a different, joystick-subsystem backend).
Comment 1 David Ludwig 2020-04-18 16:13:38 UTC 
Created attachment 4310 [details]
Fix #1: use SDL_GetNextJoystickInstanceID() for alloc'ing joystick-ids in Emscripten joystick backend

Here is an attempt at a fix.  It seems to work fine for me, however it could, perhaps, use more testing, and maybe review by someone more familiar with SDL2's Emscripten joystick backend.