Programming Input Devices

Getting the device state Schemes for processing input – Polling – Callbacks Ways to intercept messages from input devices – WM_INPUT – WM_MOUSEMOVE – DirectInput

Basic Mouse Interaction Double Click – WM_LBUTTONDBLCLK – WM_MBUTTONDBLCLK – WM_RBUTTONDBLCLK Button Press – WM_LBUTTONDOWN – WM_MBUTTONDOWN – WM_BBUTTONDOWN Button Release – WM_LBUTTONUP – WM_MBUTTONUP – WM_RBUTTONUP WM_MOUSEMOVE WM_NCMOUSEMOVE

Keyboard Input Key inputs are handled through windows messages: – WM_KEYDOWN – WM_KEYUP – WM_CHAR The way the application uses the keyboard input will dictate which of these three inputs will be used – Using only WM_CHAR can enable Windows to factor in other events or keystrokes such as Ctrl or Shift keys being pressed

Working with Keyboard Character Code – ASCII or Unicode char. It is usually the value returned by the C function getchar() Virtual scan code – This is the value sent in the wParam variable for WM_CHAR, WM_KEYDOWN and WM_KEYUP messages OEM scan code – This is the scan code provided by the OEM. It is useful only if a code is required for a particular type of keyboard.

The lParam Variable This 32-bit variable, with 6 fields, is passed to the WndProc() – Bit 0-15 Repeat count; the number of times of keystroke is repeated – Bit bit OEM scan code – Bit 24 Extended key flag: 1 – extended key; 0 – otherwise – Bit Reserved – Bit 29 Context code: 1 – if Alt key is pressed; 0 – otherwise – Bit 30 Previous key state: 0 -- previous key up, 1 – previous key down – Bit 31 Transition state: 0 – WM_KEYDOWN, 1 – WM_KEYUP

Keystroke Messages Keystroke messages come in the form of – WM_KEYDOWN – WM_KEYUP – WM_SYSKEYDOWN – WM_SYSKEYUP All keys produce WM_KEYDOWN and WM_KEYUP messages, except – Alt and F10

Keystroke Messages cont. OEM – identifies the key to the keyboard BIOS Extended key flag – allows application to recognize duplicate keys. For these, the value is 1 – Ctrl key on right side of keyboard – Home, End, Insert, Delete, Page Up, Page Down – Number and arrow keys – Enter and forward slash (/) Transition state, previous key state, and context code are generally disregarded

Key Handling Notes WM_SYSKEYDOWN and WM_SYSKEYUP should not be processed in most cases by your code – These must eventually get to ::DefWindowProc, system keyboard commands such as Alt-Tab and Alt-Esc will stop working Failure to pass these messages to the system can result in unusual and unreliable behavior

Capturing Special keys Ctrl keys – wParam and extended bit Shift keys – wParam and Virtual key mapping Alt keys – Listen to WM_SYSCOMMAND

LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam) { int x=0,y=0; int repeat=0,extended=0,ext = 0,scanCode =0, wasDown=0; char text[100]; switch(message) {

case WM_CHAR: { repeat = LOWORD(lParam); scanCode = HIWORD(lParam)&0x00FF; extended = (HIWORD(lParam) >>8 ) &1; wasDown = (HIWORD(lParam)>>30)&1; sprintf(text,"WM_CHAR : Code == %d '%c' Repeat == %d SCANCODE == %d Extended = %d wasDown == %d ",wParam,wParam,repeat,extended,wasDown); MessageBox(hWnd, text,"Keyboard Event Handling",MB_OK|MB_ICONINFORMATION); } break;

case WM_KEYDOWN: { repeat = LOWORD(lParam); scanCode = HIWORD(lParam)&0x00FF; extended = (HIWORD(lParam)>>8)&1; wasDown = (HIWORD(lParam)>>30)&1; if(wParam == 17) // for Ctrl key if(extended == 1) MessageBox (hWnd, "Right control key Pressed", "Title", MB_OK|MB_ICONINFORMATION); else MessageBox (hWnd, "Left control key Pressed", "Title", MB_OK|MB_ICONINFORMATION);

if(wParam == 16) {// Shift key UINT virtualKey = MapVirtualKey(scanCode,3); if(virtualKey == VK_RSHIFT) MessageBox( hWnd,"Right Shift key Pressed","Title", MB_OK|MB_ICONINFORMATION); if(virtualKey == VK_LSHIFT) MessageBox(hWnd,"Left Shift key Pressed","Title", MB_OK|MB_ICONINFORMATION); } else { sprintf(text,"WM_KEYDOWN : Code == %d '%c' Repeat == %d scancode = %d Extended = %d ",wParam, wParam, repeat, extended); MessageBox(hWnd, text,"Keyboard Event Handling", MB_OK|MB_ICONINFORMATION); } } break;

case WM_SYSCOMMAND: MessageBox(hWnd,"Alt Key pressed", "Title", MB_OK|MB_ICONINFORMATION); break; case WM_NCMOUSEMOVE: MessageBox(hWnd,"Moved on the Title bar","Mouse Event", MB_OK|MB_ICONINFORMATION); break;

case WM_LBUTTONDOWN:{ x = LOWORD(lParam); y = HIWORD(lParam); sprintf(text,"Mouse left Click x == %d, y == %d",x,y); MessageBox(hWnd, text, "Mouse Event", MB_OK|MB_ICONINFORMATION); } break;