101 lines
2.6 KiB
C
101 lines
2.6 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#define XSIZE 2560
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#define YSIZE 2048
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#define MAXITER 255
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double xleft=-2.01;
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double xright=1;
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double yupper,ylower;
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double ycenter=1e-6;
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double step;
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int pixel[XSIZE*YSIZE];
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#define PIXEL(i,j) ((i)+(j)*XSIZE)
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typedef struct {
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double real,imag;
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} complex_t;
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void calculate() {
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for(int i=0;i<XSIZE;i++) {
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for(int j=0;j<YSIZE;j++) {
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/* Calculate the number of iterations until divergence for each pixel.
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If divergence never happens, return MAXITER */
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complex_t c,z,temp;
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int iter=0;
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c.real = (xleft + step*i);
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c.imag = (ylower + step*j);
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z = c;
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while(z.real*z.real + z.imag*z.imag < 4) {
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temp.real = z.real*z.real - z.imag*z.imag + c.real;
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temp.imag = 2*z.real*z.imag + c.imag;
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z = temp;
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if(++iter==MAXITER) break;
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}
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pixel[PIXEL(i,j)]=iter;
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}
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}
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}
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typedef unsigned char uchar;
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/* save 24-bits bmp file, buffer must be in bmp format: upside-down */
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void savebmp(char *name,uchar *buffer,int x,int y) {
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FILE *f=fopen(name,"wb");
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if(!f) {
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printf("Error writing image to disk.\n");
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return;
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}
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unsigned int size=x*y*3+54;
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uchar header[54]={'B','M',size&255,(size>>8)&255,(size>>16)&255,size>>24,0,
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0,0,0,54,0,0,0,40,0,0,0,x&255,x>>8,0,0,y&255,y>>8,0,0,1,0,24,0,0,0,0,0,0,
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0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
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fwrite(header,1,54,f);
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fwrite(buffer,1,XSIZE*YSIZE*3,f);
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fclose(f);
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}
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/* given iteration number, set a colour */
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void fancycolour(uchar *p,int iter) {
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if(iter==MAXITER);
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else if(iter<8) { p[0]=128+iter*16; p[1]=p[2]=0; }
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else if(iter<24) { p[0]=255; p[1]=p[2]=(iter-8)*16; }
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else if(iter<160) { p[0]=p[1]=255-(iter-24)*2; p[2]=255; }
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else { p[0]=p[1]=(iter-160)*2; p[2]=255-(iter-160)*2; }
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}
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int main(int argc,char **argv) {
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if(argc==1) {
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puts("Usage: MANDEL n");
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puts("n decides whether image should be written to disk (1=yes, 0=no)");
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return 0;
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}
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/* Calculate the range in the y-axis such that we preserve the
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aspect ratio */
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step=(xright-xleft)/XSIZE;
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yupper=ycenter+(step*YSIZE)/2;
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ylower=ycenter-(step*YSIZE)/2;
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calculate();
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if(strtol(argv[1],NULL,10)!=0) {
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/* create nice image from iteration counts. take care to create it upside
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down (bmp format) */
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unsigned char *buffer=calloc(XSIZE*YSIZE*3,1);
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for(int i=0;i<XSIZE;i++) {
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for(int j=0;j<YSIZE;j++) {
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int p=((YSIZE-j-1)*XSIZE+i)*3;
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fancycolour(buffer+p,pixel[PIXEL(i,j)]);
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}
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}
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/* write image to disk */
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savebmp("mandel2.bmp",buffer,XSIZE,YSIZE);
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}
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return 0;
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}
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