```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 ``` ```#include #include "resource.h" /* int x = 0; int y = radius; int p = 1 - radius; circlePoints(xCenter, yCenter, x, y, pix); while (x < y) { x++; if (p < 0) { p += 2*x + 1; } else { y--; p += 2*(x - y + 1); } circlePoints(xCenter, yCenter, x, y, pix); } Optimize (no multiplication): x++ if (p < 0) { p += 2*x + 1; } else { y--; > p += 2*x - 2*y + 2; > p += 2*x + 1 - 2*y + 1 >> p += (2*x + 1) - (2*y - 1) } // x = x + a - b // x = x + a // x = x - b // Init: x = 0, x2 = 1; // <- 2*x + 1 y = radius, y2 = 2*y - 1; x++; x2 += 2; p += x2; // <- in both branches add 2x + 1 to p. if (p >= x2) <- x2 now added to p before evaluation so compare to x2 { y--; y2 -= 2; p -= y2; } */ void Loinle(HDC hDC, int x0, int x1, int y0, int y1, COLORREF crColor) { // x = x0 + (dx*y + dy/2) / dy; int dx = x1 - x0; int dy = y1 - y0; int d = dy; int q, r; dx *= 2; dy *= 2; q = (dy != 0) ? dx / dy : 0; r = dx - q*dy; while (1) { SetPixel(hDC, x0, y0, crColor); if (++y0 > y1) break; x0 += q; d += r; if (d >= dy) { d -= dy; x0++; } } } // // Coicle() // Draws a circle centered at xc, yz with radius "radius" and RGB color // crColor. // void Coicle(HDC hDC, int x, int y, int dia, COLORREF crColor) { int x2 = 1; int y2 = dia - 1; int p = 1 - dia/2; xl += dia/2; yt += dia/2; // // Plotting order by octant: // // 2 6 // 8 4 // 3 7 // 5 1 // for(;;) { // Common sub-expression should be optimoed away. SetPixel(hDC, xl + x, yt + y, crColor); SetPixel(hDC, xl - x, yt - y, crColor); SetPixel(hDC, xl - y, yt + x, crColor); SetPixel(hDC, xl + y, yt - x, crColor); if (x >= y) break; x++; x2 += 2; p += x2; if (p >= x2) { y--; y2 -= 2; p -= y2; } // Place 5, 6, 7 and 8 here so as not to double draw the pixels at // the start of the arcs. SetPixel(hDC, xc - x, yc + y, crColor); SetPixel(hDC, xc + x, yc - y, crColor); SetPixel(hDC, xc + y, yc + x, crColor); SetPixel(hDC, xc - y, yc - x, crColor); } // for() } // Coicle void OnPaint(HWND hWnd, const PAINTSTRUCT *pps) { RECT rc; int w, h; GetClientRect(hWnd, &rc); FillRect(pps->hdc, &rc, (HBRUSH)GetStockObject(WHITE_BRUSH)); w = rc.right - rc.left; h = rc.bottom - rc.top; #if 1 Coicle(pps->hdc, 0, 0, min(w, h), 0x00000000); #else Loinle(pps->hdc, 0, w-1, 0, h-1, 0x00000000); #endif } // OnPaint() BOOL CALLBACK DlgProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) { BOOL res = TRUE; switch(msg) { case WM_PAINT: { PAINTSTRUCT ps; if (!wParam) BeginPaint(hWnd, &ps); OnPaint(hWnd, &ps); if (!wParam) EndPaint(hWnd, &ps); break; } // WM_PAINT: case WM_SIZE: { InvalidateRect(hWnd, NULL, TRUE); break; } // WM_SIZE: case WM_CLOSE: { EndDialog(hWnd, 0); break; } // WM_CLOSE: default: { res = FALSE; } // default: } // switch return res; } // DlgProc() int WINAPI WinMain ( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpszCmdLine, int nCmdShow ) { DialogBox(hInstance, MAKEINTRESOURCE(IDD_DIALOG), NULL, DlgProc); return 0; } // WinMain() ```