Go deep into the SetOP2 Function

SetROP2 function: sets the foreground painting mode. The currently drawn pixel value is the inverse of the current screen pixel value, so that the last painting result can be erased:

Simulate the BLOCKOUT program in chapter 7 of windows programming:

Code:

 

[C-sharp]View plaincopyprint?

1. # Include <windows. h>
3. Lresult callback wndproc (HWND, UINT, WPARAM, LPARAM );
5. Int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
6. {
7. Static TCHAR szAppName [] = TEXT ("BlokOut1 ");
8. HWND hwnd;
9. MSG msg;
10. WNDCLASS wndclass;
12. Wndclass. style = CS_HREDRAW | CS_VREDRAW;
13. Wndclass. lpfnWndProc = wndproc;
14. Wndclass. cbClsExtra = 0;
15. Wndclass. cbWndExtra = 0;
16. Wndclass. hInstance = hInstance;
17. Wndclass. hIcon = LoadIcon (NULL, IDI_APPLICATION );
18. Wndclass. hCursor = LoadCursor (NULL, IDC_ARROW );
19. Wndclass. hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH );
20. Wndclass. lpszMenuName = NULL;
21. Wndclass. lpszClassName = szAppName;
23. If (! RegisterClass (& wndclass ))
24. {
25. MessageBox (NULL, TEXT ("Program requires Windows NT! "),
26. SzAppName, MB_ICONERROR );
27. Return 0;
28. }
30. Hwnd = CreateWindow (szAppName, TEXT ("Mouse Button Demo "),
31. WS_OVERLAPPEDWINDOW,
32. CW_USEDEFAULT, CW_USEDEFAULT,
33. CW_USEDEFAULT, CW_USEDEFAULT,
34. NULL, NULL, hInstance, NULL );
36. ShowWindow (hwnd, SW_SHOWNORMAL );
37. UpdateWindow (hwnd );
39. While (GetMessage (& msg, NULL, 0, 0 ))
40. {
41. TranslateMessage (& msg );
42. DispatchMessage (& msg );
43. }
44. Return msg. wParam;
45. }
47. Void Draw (HWND hwnd, POINT ptbeg, POINT ptend)
48. {
49. HDC hdc;
50. Hdc = GetDC (hwnd );
51. SetROP2 (hdc, R2_NOT); // you can comment out this line and check the result.
52. SelectObject (hdc, GetStockObject (NULL_BRUSH ));
53. Rectangle (hdc, ptbeg. x, ptbeg. y, ptend. x, ptend. y );
54. ReleaseDC (hwnd, hdc );
55. }
57. Lresult callback wndproc (HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam)
58. {
59. Static POINT ptbeg, ptend, Boxbeg, Boxend;
60. Static BOOL flag1, flag2;
61. HDC hdc;
62. PAINTSTRUCT ps;
63. Switch (message)
64. {
65. Case WM_LBUTTONDOWN:
66. Ptbeg. x = ptend. x = LOWORD (lparam );
67. Ptbeg. y = ptend. y = HIWORD (lparam );
69. Draw (hwnd, ptbeg, ptend );
70. Flag1 = TRUE;
71. SetCursor (LoadCursor (NULL, IDC_CROSS ));
73. Return 0;
74. Case WM_MOUSEMOVE:
75. If (flag1)
76. {
77. SetCursor (LoadCursor (NULL, IDC_CROSS ));
78. Draw (hwnd, ptbeg, ptend );
79. Ptend. x = LOWORD (lparam );
80. Ptend. y = HIWORD (lparam );
81. Draw (hwnd, ptbeg, ptend );
82. }
83. Return 0;
84. Case WM_LBUTTONUP:
85. If (flag1)
86. {
87. SetCursor (LoadCursor (NULL, IDC_ARROW ));
88. Draw (hwnd, ptbeg, ptend );
89. Boxbeg = ptbeg;
90. Boxend. x = LOWORD (lparam );
91. Boxend. y = HIWORD (lparam );
92. Flag1 = FALSE;
93. Flag2 = TRUE;
94. InvalidateRect (hwnd, NULL, TRUE );
95. }
96. Return 0;
97. Case WM_PAINT:
98. If (flag2)
99. {Hdc = BeginPaint (hwnd, & ps );
100. SelectObject (hdc, GetStockObject (BLACK_BRUSH ));
101. // Draw (hwnd, Boxbeg, Boxend );
102. Rectangle (hdc, Boxbeg. x, Boxbeg. y, Boxend. x, Boxend. y );
103. EndPaint (hwnd, & ps );
104. }
105. Return 0;
106. Case WM_DESTROY:
107. PostQuitMessage (0 );
108. Return 0;
109. }
110. Return DefWindowProc (hwnd, message, wparam, lparam );

}