Relative mouse mode broken on macOS

[rom1v]

The cursor visibility and the state of relative mouse mode are not consistent on macOS.

Here is a minimal sample: https://github.com/rom1v/sample-relativemouse

Run the app from a console (keep the console visible to read the logs), and press Alt while the SDL window is focused to toggle "relative mouse mode".

It is expected that when relative mouse mode is enabled, the cursor is hidden.

With SDL 2.0.20, it works correctly on Linux.

But on macOS, relative mouse mode and cursor visibility are not consistent: sometimes relative mouse mode is enabled but the cursor is still visible.

[rom1v]

FYI, here is a workaround on the client side:

diff --git a/main.c b/main.c
index 50aa372..aa2f2a2 100644
--- a/main.c
+++ b/main.c
@@ -51,6 +51,19 @@ int main() {
                 // Toggle relative mode on Alt
                 if (event.key.keysym.sym == SDLK_LALT) {
                     SDL_bool new_mode = !SDL_GetRelativeMouseMode();
+                    if (new_mode) {
+                        int mouse_x, mouse_y;
+                        SDL_GetGlobalMouseState(&mouse_x, &mouse_y);
+
+                        int x, y, w, h;
+                        SDL_GetWindowPosition(window, &x, &y);
+                        SDL_GetWindowSize(window, &w, &h);
+
+                        if (mouse_x < x || mouse_x >= x + w ||
+                                mouse_y < y || mouse_y >= y + h) {
+                            SDL_WarpMouseInWindow(window, w/2, h/2);
+                        }
+                    }
                     SDL_SetRelativeMouseMode(new_mode);
                     printf("switch relative mode to %s\n",
                            new_mode ? "true" : "false");

Since it fails only when the cursor is not in the window when enabling relative mode, moving the cursor beforehand avoids the problem.