1. 1 Windows GDI Programming CIS 487/587 Bruce R. Maxim UM-Dearborn

2. 2 Validating Whenever either you or Windows disturbs a window a WM_PAINT message is sent The area to be repainted is the invalid rectangle The coordinates of the invalid rectangle are shipped with the WM_PAINT message as part of the validating process

3. 3 Processing WM_PAINT BeginPaint( ) … EndPaint( ) –Advantage: all needed validating done automatically –Disadvantage: invalid rectangle is same as clipping rectangle (can’t draw outside invalid rectangle) –This approach fools Windows into believing you fixed the invalid rectangle whether you have drawn anything or not

4. 4 Processing WM_PAINT GetDC( ) … ReleaseDC( ) –Advantage:you can draw outside the invalid rectangle –Disadvantage: you need to validate every rectangle manually using ValidateRect( ) Note: With either method you need to be sure that windows does not fill in your Background to avoid losing your drawing

5. 5 Invalidating Entire Window case WM_PAINT: { // NULL is pointer to invalid rectangle // meaning entire window ValidateRect(hwnd,NULL); // simply validate the window hdc = BeginPaint(hwnd,&ps); // fixes go here EndPaint(hwnd,&ps); // end painting return(0); // return success } break;

6. 6 Validating Entire Window case WM_PAINT: { // NULL is pointer to invalid rectangle // meaning entire window ValidateRect(hwnd,NULL); // simply validate the window without // doing any drawing return(0); // return success } break;

7. 7 Avoid Repaint case WM_PAINT: { hdc = GetDC(hwnd); // do graphics here ReleaseDC(hwnd,hdc); // validate the window to clear message ValidateRect(hwnd,hdc); return(0); // return success } break;

8. 8 Display Surface Basics Resolutions in pixels 640x480, 800x600, 1024x768, … Color depth (# color bits per pixel) 6, 16, 24, 32 Color space (actual # available colors) 8 bits = 256 colors, 16 bits = 65536

9. 9 Display Modes RGB mode –True RGB values are encoded for each pixel displayed Palletized mode –Color indirection scheme –256 colors available –Value 0 to 255 is stored with each pixel –Color value looked up in CLUT

10. 10 Color Objects Windows uses to data structures –COLOREF: byte structure allows you to create colors on the fly –PALETTEENTRY: all creation of pallets with control flag components Complete control of pallets is best done using DirectX

11. 11 Drawing Text TextOut( ) –No formatting or processing of text string is done before it is displayed DrawText( ) –Allows justification, clipping, etc. prior to displaying text string

12. 12 LaMothe Examples

13. 13 TextOut Example main_window_handle = hwnd; // save main window handle HDC hdc = GetDC(hwnd); // get the dc and hold it // set the foreground color to random SetTextColor(hdc, RGB(rand()%256,rand()%256,rand()%256)); // set the background color to black SetBkColor(hdc, RGB(0,0,0)); // finally set the transparency mode to transparent SetBkMode(hdc, TRANSPARENT); // draw some text at a random location TextOut(hdc,rand()%400,rand()%400, "GDI Text Demo!", strlen("GDI Text Demo!")); ReleaseDC(hwnd,hdc); // release the dc

14. 14 What about WM_PAINT? case WM_PAINT: { // simply validate the window hdc = BeginPaint(hwnd,&ps); // you would do all your painting here EndPaint(hwnd,&ps); // return success return(0); } break;

15. 15 Additional Issues You should consider saving the old values for foreground, ground, and transparency so that you can restore them after you set them Example we might declare the following: COLORREF old_fcolor, // old foreground old_bcolor; // old background int old_tmode; // old transparency

16. 16 TextOut Example 2 main_window_handle = hwnd; // save main window handle HDC hdc = GetDC(hwnd); // get the dc and hold it // save old attributes and set new old_fcolor = SetTextColor(hdc,RGB(255,255,255)); old_bcolor = SetBkColor(hdc, RGB(0,0,0)); old_tmode= SetBkMode(hdc, TRANSPARENT); // draw some text at a random location TextOut(hdc, 120, 200, “Hello", strlen(“Hello")); // Restore the old values SetTextColor(hdc, old_fcolor); SetBkColor(hdc, old_bcolor); SetBkMode(hdc, old_tmode); ReleaseDC(hwnd,hdc); // release the dc

17. 17 Text Metrics The function GetTextMetrics can be used to query the system for things like –Font height –Average width –Max width –First character defined in font –Last character defined in font Set of values returned in fields of a parameter of type tagTEXTMETRIC

18. 18 Drawing Shapes GDI allows you to draw things like –Points –Lines –Circles and ellipses –Rectangles –Curves –Polygons –Bitmaps –Metafiles (instructions that can be “replayed”)

19. 19 Pens Pens are GDI objects used to draw lines Pens have two attributes –RGB color –Styles like PS_DASH - - - - PS_DOT.... PS_DASHDOT _. _. PS_NULL

20. 20 Using a Pen // get the graphics device context hdc = GetDC(hwnd); // create a red colored pen HPEN red_pen = CreatePen(PS_SOLID,1,RGB(255, 0, 0)); // selecting pen and saving old value HPEN old_hpen = (HPEN)SelectObject(hdc,red_pen); // draw with pen // deleting pen SelectObject(hdc,old_hpen); DeleteObject(red_ pen); // release the device context ReleaseDC(hwnd,hdc)

21. 21 Brushes Brushes are used to fill in line objects Examples // creating a solid brush HBRUSH blue_brush = CreateSolidBrush(RGB(0,0,255)); // creating a patterned brush HBRUSH green_brush = CreateHatchBrush(HS_DIAGCROSS, RGB(0,255,0)); // creating a bitmap brush (8x8) HBRUSH bitmap_brush = CreatePatternBrush(hBitMap);

22. 22 Selecting and Destroying Brushes // select brush and save old brush HBRUSH old_brush = SelectObject(hdc, red_brush); // use the brush // restore old brush SelectObject(hdc, old_brush); DeleteObject(red_brush);

23. 23 Plotting Points hdc = GetDC(hwnd); // get the dc for the window // draw 1000 pixels for (int index=0; index < 1000; index++) { // get random position int x = rand()%400; int y = rand()%300; COLORREF color = RGB(rand()%255,rand()%255,rand()%255); SetPixel(hdc, x,y, color); } // end for index ReleaseDC(hwnd, hdc); // release the dc

24. 24 Drawing Lines // create pen HPEN red_pen = CreatePen(PS_SOLID,1,RGB(255, 0, 0)); // selecting pen and saving old value SelectObject(hdc,red_pen); // move to starting point MoveToEx(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT,NULL); // draw the line LineTo(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT);

25. 25 Drawing Rectangles hdc = GetDC(hwnd); // get the graphics device context RECT rect; // used to hold rect info // create a random rectangle rect.left = rand()% WINDOW_WIDTH; rect.top = rand()% WINDOW_HEIGHT; rect.right = rand()% WINDOW_WIDTH; rect.bottom = rand()% WINDOW_HEIGHT; // create a random brush HBRUSH hbrush = CreateSolidBrush(RGB(100, 50, 80)); // draw either a filled rect or a wireframe rect if ((rand()%2)==1) FillRect(hdc,&rect,hbrush); else FrameRect(hdc,&rect,hbrush); DeleteObject(hbrush); // now delete the brush ReleaseDC(hwnd,hdc);// release the device context

26. 26 Drawing Circles and Ellipses Circle is special case of ellipse To draw a circle at (100, 100) with diameter 20 Ellipse(hdc, 90, 90,110, 110); To draw an ellipse centered at (100, 100) with major axis 100 and minor axis 60 Ellipse(hdc, 100-50, 100-30, 100+50, 100+30);

27. 27 Bouncing Ball An old computer animators trick is to – Draw an object using the foreground color –Erase object by redrawing in the background color –Change the object screen coordinates and draw again in the foreground color We can make use of this trick and use Ellipse to draw a bouncing ball

28. 28 Bouncing Ball hdc = GetDC(hwnd); // create the pens and brushes HPEN white_pen = CreatePen(PS_SOLID, 1, RGB(255,255,255)); HPEN black_pen = CreatePen(PS_SOLID, 1, RGB(0,0,0)); HBRUSH green_brush = CreateSolidBrush(RGB(0,255,0)); HBRUSH black_brush = CreateSolidBrush(RGB(0,0,0)); // starting position of ball int ball_x = WINDOW_WIDTH/2; int ball_y = WINDOW_HEIGHT/2; // initial velocity of ball int xv = -4+rand() % 8; int yv = -4+rand() % 8;

29. 29 Bouncing Ball // ERASE the last position of the ball // first select the black pen and brush into context SelectObject(hdc, black_pen); SelectObject(hdc, black_brush); // draw the ball Ellipse(hdc, ball_x, ball_y, ball_x + 32, ball_y + 32); // MOVE the ball ball_x+=xv; ball_y+=yv; // test for collisions, first x-axis if (ball_x WINDOW_WIDTH - 32) { // invert x-velocity of ball xv=-xv; // push ball back ball_x+=xv; } // end if else // test for y-axis collisions if (ball_y WINDOW_HEIGHT - 32) { // invert y-velocity of ball yv=-yv; // push ball back ball_y+=yv; } // end if // now select the green and white colors for brush and pen SelectObject(hdc, white_pen); SelectObject(hdc, green_brush); // DRAW the ball Ellipse(hdc, ball_x, ball_y, ball_x + 32, ball_y + 32); // main game processing goes here if (KEYDOWN(VK_ESCAPE)) SendMessage(hwnd, WM_CLOSE, 0,0); // slow system down a little Sleep(10); } // end while // delete all the objects DeleteObject(white_pen); DeleteObject(black_pen); DeleteObject(green_brush); DeleteObject(black_brush); // release the device context ReleaseDC(hwnd,hdc);

30. 30 Bouncing Ball // ERASE the last position of the ball // first select the black pen and brush into context SelectObject(hdc, black_pen); SelectObject(hdc, black_brush); // draw the ball Ellipse(hdc, ball_x, ball_y, ball_x + 32, ball_y + 32); // MOVE the ball ball_x+=xv; ball_y+=yv;

31. 31 Bouncing Ball // test for collisions, first x-axis if (ball_x WINDOW_WIDTH - 32) { xv=-xv; // invert x-velocity of ball ball_x+=xv; // push ball back } // end if else // test for y-axis collisions if (ball_y WINDOW_HEIGHT - 32) { yv=-yv; // invert y-velocity of ball ball_y+=yv; // push ball back } // end if

32. 32 Bouncing Ball // select the green and white colors for brush and pen SelectObject(hdc, white_pen); SelectObject(hdc, green_brush); // DRAW the ball Ellipse(hdc, ball_x, ball_y, ball_x + 32, ball_y + 32); DeleteObject(white_pen); // delete all the objects DeleteObject(black_pen); DeleteObject(green_brush); DeleteObject(black_brush); ReleaseDC(hwnd,hdc); // release the device context