I've been getting stuck and confused, or confusing myself a couple times over the last eight weeks with my code ~= HMH days 16 - 20. For the most part things had been going really smoothly until the last three weeks, especially the last seven days, I struggled with keyboard input on the SDL2 platform. And turns out there is a good reason why.
For libsdl2 v2.0.4 and 2.0.5, when I pressed and held a key, it would report only one event with the repeat flag set after the system auto-repeat delay (500ms). Then it spammed keydown & pressed - keyup & released events with the repeat flag unset, which continued for up to a couple of seconds after the key was physically released. There's no way I could filter these events
This started after adding the SDL2 equivalent sleep function to return CPU to the system after each frame was processed. Prior to that, the bug wasn't showing (although I recall the event flags in my debug printouts were still wrong). I very soon dropped the idea that the sleep was the root cause (else developing SDL2 on Linux would be completely untenable).
I tried everything. I fiddled with the auto-repeat settings, I tried to get input from X11 instead. I even wrote code to get events directly from the evdev kernel interface. Of course, the kernel events were perfect. But behind a display server that's behind a window manager that's behind <yet another interface> ... that's behind SDL2, polling input directly from the kernel breaks the security model of the GUI stack. Even though my code POC'd my suspicions, I couldn't distribute games that uses it (although a handmade Linux desktop could ;)
Finally, I found a bug report for SDL2 last night. It was exactly this issue.
https://bugzilla.libsdl.org/show_bug.cgi?id=3472
And there is a patch that I tested locally on my system with success.
https://bugzilla-attachments.libsdl.org/attachment.cgi?id=2594
Buggy Example:
Correct Example:
For libsdl2 v2.0.4 and 2.0.5, when I pressed and held a key, it would report only one event with the repeat flag set after the system auto-repeat delay (500ms). Then it spammed keydown & pressed - keyup & released events with the repeat flag unset, which continued for up to a couple of seconds after the key was physically released. There's no way I could filter these events
This started after adding the SDL2 equivalent sleep function to return CPU to the system after each frame was processed. Prior to that, the bug wasn't showing (although I recall the event flags in my debug printouts were still wrong). I very soon dropped the idea that the sleep was the root cause (else developing SDL2 on Linux would be completely untenable).
I tried everything. I fiddled with the auto-repeat settings, I tried to get input from X11 instead. I even wrote code to get events directly from the evdev kernel interface. Of course, the kernel events were perfect. But behind a display server that's behind a window manager that's behind <yet another interface> ... that's behind SDL2, polling input directly from the kernel breaks the security model of the GUI stack. Even though my code POC'd my suspicions, I couldn't distribute games that uses it (although a handmade Linux desktop could ;)
Finally, I found a bug report for SDL2 last night. It was exactly this issue.
https://bugzilla.libsdl.org/show_bug.cgi?id=3472
And there is a patch that I tested locally on my system with success.
https://bugzilla-attachments.libsdl.org/attachment.cgi?id=2594
Buggy Example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 | TS: 4266 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4305 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 4305 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4305 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4332 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4332 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4372 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 4372 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4372 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4399 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4399 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4439 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 4439 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4439 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4467 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4467 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4467 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4506 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4533 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4567 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4606 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4640 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4667 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4700 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4739 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4772 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4800 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4833 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4873 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4906 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 4933 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 4967 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 5005 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 5039 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 5066 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 |
Correct Example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 | TS: 4385 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 TS: 5383 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 0 TS: 5885 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 5919 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 5952 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 5985 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6018 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6051 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6084 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6118 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6151 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6184 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6217 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6250 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6285 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6317 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6350 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6383 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6417 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6450 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6483 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6516 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6551 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6584 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6617 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6650 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6683 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6717 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6751 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6785 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6818 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6851 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6885 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6918 KeyUp: 0 KeyDwn: 1 Pressed: 1 Release: 0 Repeat: 1 TS: 6952 KeyUp: 1 KeyDwn: 0 Pressed: 0 Release: 1 Repeat: 0 |
This was probably my fault, sorry!
I submitted a few patches to SDL in 2.0.4 to correct a couple of XIM related issues, and they were included in 2.0.5. Unfortunately these changes seemed to have some bad interactions with certain input methods and caused the broken key repeats.
I wrote the patch you linked pretty soon after 2.0.5 was released and I was made aware of the problem, but I guess it might not have been included in every distro's copy of 2.0.5 yet.
You said this also happened in 2.0.4 though, so maybe there was some other older issue that my patch fixed? In any case, if you run with XMODIFIERS="@im=none" (or maybe unset) then there shouldn't be any repeat problems - you could setenv() this before initing SDL I suppose.
I submitted a few patches to SDL in 2.0.4 to correct a couple of XIM related issues, and they were included in 2.0.5. Unfortunately these changes seemed to have some bad interactions with certain input methods and caused the broken key repeats.
I wrote the patch you linked pretty soon after 2.0.5 was released and I was made aware of the problem, but I guess it might not have been included in every distro's copy of 2.0.5 yet.
You said this also happened in 2.0.4 though, so maybe there was some other older issue that my patch fixed? In any case, if you run with XMODIFIERS="@im=none" (or maybe unset) then there shouldn't be any repeat problems - you could setenv() this before initing SDL I suppose.
(╯°□°)╯︵ ┻━┻
