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1 /*
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2 A simple interactive mandelbrot fractal explorer
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3 Copyright (C) John Tsiombikas <nuclear@member.fsf.org>
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4
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5 This program is free software: you can redistribute it and/or modify
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6 it under the terms of the GNU General Public License as published by
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7 the Free Software Foundation, either version 3 of the License, or
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8 (at your option) any later version.
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9
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10 This program is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU General Public License for more details.
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14
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15 You should have received a copy of the GNU General Public License
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16 along with this program. If not, see <http://www.gnu.org/licenses/>.
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17 */
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18 #include "mbrot.h"
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19 #include "palette.h"
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20
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21 static int mandelbrot(double cx, double cy, int iter);
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22
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23 void draw_mandelbrot(unsigned char *pix, int xsz, int ysz, struct area *area, int iter)
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24 {
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25 int i, j;
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26 double x, y, dx, dy;
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27
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28 dx = area->width / (double)xsz;
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29 dy = area->height / (double)ysz;
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30
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31 y = area->y;
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32 for(i=0; i<ysz; i++) {
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33 x = area->x;
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34 for(j=0; j<xsz; j++) {
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35 int res = mandelbrot(x, y, iter);
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36 /* visualize according to the number of iterations
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37 * required to determine membership in the mandelbrot set.
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38 * Members of the set will have res = iter and so col = PAL_SIZE-1
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39 */
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40 int col = (PAL_SIZE - 1) * res / iter;
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41 *pix++ = palette[col].r;
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42 *pix++ = palette[col].g;
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43 *pix++ = palette[col].b;
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44 *pix++ = 0;
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45
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46 x += dx;
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47 }
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48 y += dy;
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49 }
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50 }
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51
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52 static int mandelbrot(double cx, double cy, int iter)
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53 {
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54 int i;
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55 double zx, zy; /* complex number Z */
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56
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57 /* start with Z0 = C */
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58 zx = cx;
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59 zy = cy;
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60
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61 for(i=0; i<iter; i++) {
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62 /* calculate Zn+1 = Zn * Zn + C */
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63 double x = (zx * zx - zy * zy) + cx;
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64 double y = (zy * zx + zx * zy) + cy;
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65 zx = x;
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66 zy = y;
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67
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68 /* escape if ||Z|| > 2 */
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69 if((x * x + y * y) > 4.0) {
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70 break;
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71 }
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72 }
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73
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74 return i;
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75 }
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