WM_INPUT

wm_input.cpp

auto className = "Window Class";
WNDCLASSA windowClass = {
  .lpfnWndProc = WndProc,
  .hInstance = GetModuleHandleA(nullptr),
  .lpszClassName = className,
};
RegisterClassA(&windowClass);
auto hwnd = CreateWindowExA(0, className, "Window Name", 0, 0, 0, 0, 0, HWND_MESSAGE, 0, 0, 0);
RAWINPUTDEVICE device{
  .usUsagePage = HID_USAGE_PAGE_GENERIC,
  .usUsage = HID_USAGE_GENERIC_MOUSE,
  .dwFlags = RIDEV_INPUTSINK,
  .hwndTarget = hwnd,
};
RegisterRawInputDevices(&device, 1, sizeof(device));

LRESULT CALLBACK WndProc(HWND hwnd, UINT event, WPARAM wparam, LPARAM lparam) {
  switch (event) {
    case WM_INPUT: {      
      static struct {
          int dx = 0;
          int dy = 0;
      } mouseInput;
      static vector<BYTE> buffer;
      UINT size{};
      GetRawInputData((HRAWINPUT)lparam, RID_INPUT, nullptr, &size, sizeof(RAWINPUTHEADER));
      buffer.reserve(size);
      auto raw = (RAWINPUT*)buffer.data();
      GetRawInputData((HRAWINPUT)lparam, RID_INPUT, raw, &size, sizeof(RAWINPUTHEADER));
      if (raw->header.dwType == RIM_TYPEMOUSE) {
        mouseInput.dx = raw->data.mouse.lLastX;
        mouseInput.dy = raw->data.mouse.lLastY;
      }
      return 0;
    }
  }
  return DefWindowProcA(hwnd, event, wparam, lparam);
}