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Implement keyboard grab support for Windows

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This is implemented via a low-level keyboard hook. Unfortunately, this is
rather invasive, but it's how Microsoft recommends that it be done [0].
We want to do as little as possible in the hook, so we only intercept a few
crucial modifier keys there, while leaving other keys to the normal event
processing flow.

We will only install this hook if SDL_HINT_GRAB_KEYBOARD=1, which is not
the default. This will reduce any compatibility concerns to just the SDL
applications that explicitly ask for this behavior.

We also remove the hook when the grab is terminated to ensure that we're
not unnecessarily staying involved in key event processing when it's not
required anymore.

[0]: https://docs.microsoft.com/en-us/windows/win32/dxtecharts/disabling-shortcut-keys-in-games
This commit is contained in:
Cameron Gutman
2021-01-22 19:40:26 -06:00
parent fd65aaa9a8
commit 8c921d8201
4 changed files with 93 additions and 0 deletions
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41
src/video/windows/SDL_windowsevents.c
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@@ -428,6 +428,47 @@ static SDL_MOUSE_EVENT_SOURCE GetMouseMessageSource()
return SDL_MOUSE_EVENT_SOURCE_MOUSE;
}
LRESULT CALLBACK
WIN_KeyboardHookProc(int nCode, WPARAM wParam, LPARAM lParam)
{
if (nCode < 0 || nCode != HC_ACTION) {
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
KBDLLHOOKSTRUCT* hookData = (KBDLLHOOKSTRUCT*)lParam;
SDL_Scancode scanCode;
switch (hookData->vkCode) {
case VK_LWIN:
scanCode = SDL_SCANCODE_LGUI;
break;
case VK_RWIN:
scanCode = SDL_SCANCODE_RGUI;
break;
case VK_LMENU:
scanCode = SDL_SCANCODE_LALT;
break;
case VK_RMENU:
scanCode = SDL_SCANCODE_RALT;
break;
case VK_LCONTROL:
scanCode = SDL_SCANCODE_LCTRL;
break;
case VK_RCONTROL:
scanCode = SDL_SCANCODE_RCTRL;
break;
default:
return CallNextHookEx(NULL, nCode, wParam, lParam);
}
if (wParam == WM_KEYDOWN || wParam == WM_SYSKEYDOWN) {
SDL_SendKeyboardKey(SDL_PRESSED, scanCode);
} else {
SDL_SendKeyboardKey(SDL_RELEASED, scanCode);
}
return 1;
}
LRESULT CALLBACK
WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{