Programming in graphical environment. Introduction

Transcription

1 Programming in graphical environment Introduction

2 The lecture Additional resources available at: Recommended books: Programming Windows - Charles Petzold Developing User Interfaces for Microsoft Windows - Everett N. McKay

3 The lecture and lab Programming Windows applications Tools and interfaces: Visual C++ (version 6.0 and.net) Win 32 Application Programming Interface (Win32 API), without additional libraries like MFC, ATL.

4 Lecture 1 Differences between console (DOS) and event-driven (Windows) application Basic structure of Windows application Message handler function Introduction to drawing

5 Differences between command line and event-driven programs

6 Console application Program flow is hard coded by the programmer Program calls operating system functions Programmer decides when to process input from the user

7 Event-driven application Program flow depends on the user Operating system sends messages to the application calling its functions User input is processed by the operating system and is delivered to the application (as messages) Most of the time application waits for the next message

8 Example Console application To check if a key was pressed, use the kbhit() function and read the key using getch() function Windows application For each key that is pressed Windows sends to your application the WM_KEYDOWN message Your application must extract the character for each message and add them to create a string

9 DOS style readline function void read_string( char *str, int maxlen ) { for ( int i = 0; i < maxlen - 1; i++ ) { str[ i ] = getche(); if ( str[ i ] == '\n' ) { str[ i ] = 0; return; } } str[ i ] = 0; }

10 Windows-style readline function char str[ 256 ]; int counter = 0; LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) { switch (message) { case WM_CHAR: if ( counter < sizeof( str )) break; case... str[ counter++ ] = wparam;

11 Structure of Windows application Initialization (done by Visual C++ wizard) Register and create main application window, direct all messages to Window Procedure Message Loop (done by Visual C++ wizard) Window procedure Every message sent to the window is handled by the window procedure. Empty window procedure is created by Visual C++ wizard. To create simple application, just write your message handlers

12 Window Procedure LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam); Window procedure is called once for each message your window receives HWND hwnd window handle UINT message message identifier WPARAM wparam first message parameter (32 bit integer) LPARAM lparam second message parameter (32 bit integer) Message parameters depend on message type.

13 Typical Window Procedure LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) { switch (message) { case WM_COMMAND: OnCommand( hwnd, wparam, lparam ); break; case WM_PAINT: OnPaint( hwnd, wparam, lparam ); break; case WM_CREATE: OnCreate( hwnd, wparam, lparam ); break; case WM_DESTROY: OnDestroy( hwnd, wparam, lparam ); break; default: return DefWindowProc(hWnd, message, wparam, lparam); } return 0; }

14 Window procedure cont. Four messages are handled: WM_COMMAND, WM_PAINT, WM_CREATE and WM_DESTROY Messages that are not handled go to DefWindowProc - default message handler Usually you will handle more than four messages, so it is better to write separate function for each message to keep the switch instruction small

15 Important messages WM_CREATE WM_DESTROY WM_PAINT WM_LBUTTONDOWN WM_LBUTTONUP WM_MOUSEMOVE WM_TIMER

16 WM_CREATE Sent right after window has been created Application should perform window initialization in WM_CREATE message handler Sample: case WM_CREATE: SetTimer( hwnd, 1, 1000, NULL ); break;

17 WM_LBUTTONDOWN Sent when left mouse button is pressed Sample: case WM_LBUTTONDOWN: int x = LOWORD( lparam ); int y = HIWORD( lparam ); break;

18 WM_TIMER Window can request WM_TIMER messages using SetTimer function UINT SetTimer( HWND hwnd, // - window handle UINT idevent, // - event id UINT uelapse, // - timeout (milisec.) TIMERPROC lptimerproc); WM_TIMER message WPARAM timer ID (used when multiple timers are present) LPARAM equal to lptimerproc

19 WM_PAINT Sent when some portion of the window is invalid and needs to be repainted Windows keeps track of invalid regions Painting is done not on screen or window but on device context

20 WM_PAINT cont. Typical WM_PAINT handler case WM_PAINT: PAINTSTRUCT ps; HDC hdc; // device context hdc = BeginPaint(hWnd, &ps); MoveToEx( hdc, 0, 0, NULL ); LineTo( hdc, 100, 100 ); EndPaint(hWnd, &ps);

21 WM_PAINT cont Windows knows when to repaint a window To force a window to be repainted, Invalidate the window. To repaint your window in response to timer messages, use: LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam) { switch (message) { case WM_TIMER: InvalidateRect( hwnd, NULL, TRUE ); break; case /* handle other messages */... default: return DefWindowProc(hWnd, message, wparam, lparam); } return 0; }