Broken mouse capture on macOS

[slouken]

Repro:

Click the left mouse button within a window and then move out of it with the button held down.

The window will not receive any more MouseMotion events despite being captured, even when moving the cursor back into the window while still holding the mouse button.

Maybe the fix:

Checking for SDL_WINDOW_MOUSE_CAPTURE in SDL_cocoawindow.m and not clearing the focus in case it's set seems to resolve the issue, but I'm not familiar enough with the codebase to consider all potential side effects - so just commenting here :)

Originally posted by @jcomusic in ea642fe

[niuzhaosen]

There is also a similar issue in sdl2, specifically manifested as MouseMotion no longer receiving when the button is held down to remove the window. Release the button and move back into the window, at which point MouseMotion can receive normally, but the MouseButton state is still held down.

[niuzhaosen]

sdl2 中也存在类似的问题，具体表现为当按住按钮以删除窗口时，MouseMotion 不再接收。释放按钮并移回窗口，此时 MouseMotion 可以正常接收，但 MouseButton 状态仍处于按住状态。

The above problem occurs on Windows and has not been attempted on other platforms yet.