DOSBox SVN suffers low graphics performance on macOS with output=opengl

[kjliew]

Homebrew had replaced sdl with sdl12-compat. Vanilla DOSBox SVN r4481 with output=opengl suffers low graphics performance. Tested using MDKDOS and PCPBENCH DOS4GW SVGA benchmarks. The drop in performance is extremely significant that OpenGL seemed Unaccelerated though GL strings returned "Apple M1 OpenGL 2.1 Metal - 76.3"

On modern Linux, sdl12-compat is superb for DOSBox SVN r4481.

MSYS2/mingw-w64 does not seem to endorse sdl12-compat. So this is not tested on Windows 10/11.

Apple M1 macOS Monterey 12.6
SDL2-2.24.0
sdl12-compat 1.2.56

[kjliew]

I figured it out that this is not sdl12-compat to blame, but due to DOSBox SVN handling of SDL_ACTIVEEVENT and changing priority on losing focus. The drop in performance reproduced exactly on Windows 11.

On Linux, DOSBox SVN has hackery that filtered out unwanted SDL_ACTIVEEVENT. The hackery was tagged with comment that this was an SDL1.2 bug on X11 but the same hackery did not fix the problem on Windows 11/macOS. There is a more elegant & easy way to deal with unwanted SDL_ACTIVEEVENT that solves this issue on Windows/macOS.

@icculus Since you had marked this issue with a milestone, perhaps you found other related issues that you planned to fix. Otherwise, feel free to close it as I think the ball should be in the court of DOSBox SVN.

[icculus]

Cool, I hadn't gotten around to debugging this yet, so I appreciate you having done this deeper research!

I'll close this issue now.