#302 Bad input lag in GNOME Wayland when run in fullscreen

[Chong Kai Xiong]

Hi,

Tux Paint exhibits unusable input lag on GNOME (Wayland) when painting with the brush or any tool with a dynamically updated cursor. The problem happens only in fullscreen.

Every mouse motion event during painting triggers brush_draw() and finishes with SDL_RendererPresent() to update the screen. Unfortunately, each call to SDL_RendererPresent() waits for VSync and this produces the horrible lag.

I've tried to use the following without success:

• Disabling VSync in SDL using SDL_SetHint(SDL_HINT_RENDER_VSYNC, "0")and SDL_RenderSetVSync(renderer, 0);
• Switching the SDL video driver between X11 and Wayland

Moving forward, I think Tux Paint's responsiveness could be improved by completing moving away from the rendering assumptions made in SDL 1.2 and decoupling frame rate from input rate.