Programming Input Devices

1. Programming Input Devices

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

3. 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

4. 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

5. 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.

6. 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 16-23     8-bit OEM scan code • Bit 24          Extended key flag: 1 – extended key; 0 – otherwise • Bit 25-28     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

7. 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 • AltandF10

8. 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

9. 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

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

11. 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) {

12. 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;

13. 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);

14. 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;

15. 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;

16. 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;