1 /*

2 A simple interactive mandelbrot fractal explorer

3 Copyright (C) John Tsiombikas <nuclear@member.fsf.org>

4

5 This program is free software: you can redistribute it and/or modify

6 it under the terms of the GNU General Public License as published by

7 the Free Software Foundation, either version 3 of the License, or

8 (at your option) any later version.

9

10 This program is distributed in the hope that it will be useful,

11 but WITHOUT ANY WARRANTY; without even the implied warranty of

12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

13 GNU General Public License for more details.

14

15 You should have received a copy of the GNU General Public License

16 along with this program. If not, see <http://www.gnu.org/licenses/>.

17 */

18 #include "mbrot.h"

19 #include "palette.h"

20

21 static int mandelbrot(double cx, double cy, int iter);

22

23 void draw_mandelbrot(unsigned char *pix, int xsz, int ysz, struct area *area, int iter)

24 {

25 int i, j;

26 double x, y, dx, dy;

27

28 dx = area->width / (double)xsz;

29 dy = area->height / (double)ysz;

30

31 y = area->y;

32 for(i=0; i<ysz; i++) {

33 x = area->x;

34 for(j=0; j<xsz; j++) {

35 int res = mandelbrot(x, y, iter);

36 /* visualize according to the number of iterations

37 * required to determine membership in the mandelbrot set.

38 * Members of the set will have res = iter and so col = PAL_SIZE-1

39 */

40 int col = (PAL_SIZE - 1) * res / iter;

41 *pix++ = palette[col].r;

42 *pix++ = palette[col].g;

43 *pix++ = palette[col].b;

44 *pix++ = 0;

45

46 x += dx;

47 }

48 y += dy;

49 }

50 }

51

52 static int mandelbrot(double cx, double cy, int iter)

53 {

54 int i;

55 double zx, zy; /* complex number Z */

56

57 /* start with Z0 = C */

58 zx = cx;

59 zy = cy;

60

61 for(i=0; i<iter; i++) {

62 /* calculate Zn+1 = Zn * Zn + C */

63 double x = (zx * zx - zy * zy) + cx;

64 double y = (zy * zx + zx * zy) + cy;

65 zx = x;

66 zy = y;

67

68 /* escape if ||Z|| > 2 */

69 if((x * x + y * y) > 4.0) {

70 break;

71 }

72 }

73

74 return i;

75 }