Grabbing WM_POINTER events with SDL3 on Windows

sdl3_win32_wmpointer.cpp

// This code does not work as-is. It is a work-in-progress in my application. You need to modify it for your application.

void handle_stylus_event(UINT uMsg, WPARAM wParam)
{
	// Wacom + [DriverSetting: Use Windows Ink] required for these events to happen at all.
	// WinTab mandatory when Windows Ink is disabled in any way.
	
	if (uMsg == WM_POINTERDEVICECHANGE)
	{
		PRINT_INPUT("DEVICE CHANGE\n");
		return;
	}

	const WORD wid = GET_POINTERID_WPARAM(wParam);
	POINTER_INFO info = {NULL};
	POINTER_PEN_INFO pen;

	if (!GetPointerInfo(wid, &info))
	{
		return; // this happens at least with finger touches with no pointer info (just weird)
	}
	else if (info.pointerType == PT_PEN && GetPointerPenInfo(wid, &pen))
	{
		bool stylus_tip = info.ButtonChangeType == POINTER_CHANGE_FIRSTBUTTON_DOWN || info.ButtonChangeType == POINTER_CHANGE_FIRSTBUTTON_UP;
		bool stylus_sidebutton_or_eraser = !stylus_tip && info.ButtonChangeType != POINTER_CHANGE_NONE;
		
		switch (uMsg)
		{
			case WM_POINTERDOWN:
			{
				if (stylus_tip)
				{
					PRINT_INPUT("WM_POINTERDOWN PEN %d\n", info.ButtonChangeType);
					input_set_stylus_pressed(true);
				}
				break;
			}
			case WM_POINTERUP:
			{
				if (stylus_tip)
				{
					PRINT_INPUT("WM_POINTERUP PEN %d\n", info.ButtonChangeType);
					input_set_stylus_pressed(false);
				}
				break;
			}
			case WM_POINTERUPDATE:
			{
				//PRINT_INPUT("WM_POINTERUPDATE PEN %.2f\n", pen.pressure/1024.0f);
				input_set_stylus_pressure(pen.pressure/1024.0f);
				break;
			}
			case WM_POINTERDEVICEINRANGE:
			case WM_POINTERENTER:
			{
				PRINT_INPUT("WM_POINTERENTER/WM_POINTERDEVICEINRANGE PEN\n");
				input_set_stylus_inrange(true);
				break;
			}
			case WM_POINTERDEVICEOUTOFRANGE:
			case WM_POINTERLEAVE:
			{
				PRINT_INPUT("WM_POINTERLEAVE/WM_POINTERDEVICEOUTOFRANGE PEN\n");
				input_set_stylus_inrange(false);
				break;
			}
			default: {}
		}
	}
	else
	{
		// info.pointerType == PT_POINTER, PT_TOUCH, PT_MOUSE, PT_TOUCHPAD
	}
}

// Use with SDL_SetWindowsMessageHook(&sdl_windowproc_callback, nullptr);
bool sdl_windowproc_callback(void *userdata, MSG *msg)
{
	MSG* sdl_msg = (MSG*)msg;
	HWND hwnd = sdl_msg->hwnd;
	UINT uMsg = sdl_msg->message;
	WPARAM wParam = sdl_msg->wParam;
	LPARAM lParam = sdl_msg->lParam;
  
	if (EasyTab && EasyTab_HandleEvent(hwnd, uMsg, lParam, wParam) == EASYTAB_OK)
	{
		input_set_stylus_pressed(EasyTab->Buttons & EasyTab_Buttons_Pen_Touch);
		input_set_stylus_pressure(EasyTab->Pressure);
	}
	else
	{
		switch (uMsg) 
		{
			case WM_POINTERENTER:
			case WM_POINTERLEAVE:
			case WM_POINTERDOWN:
			case WM_POINTERUP:
			case WM_POINTERUPDATE:
			case WM_POINTERDEVICEINRANGE:
			case WM_POINTERDEVICEOUTOFRANGE:
			case WM_POINTERDEVICECHANGE:
			{
				// pointer is triggered by both touch and pen input (we are only interested in pen here)
				handle_stylus_event(uMsg, wParam);
				break;
			}
			default: {}
		}
	}

	return true;
}