mandelbrot set issues

[2EURX9L8]

I thought I had this but I most certainly don't.

The code I have written so far does not display anything like what a mandelbrot looks like.

The assignment instructions are to write a program that creates a 512x512-pixel mandelbrot image in ppm format.

The program should accept three doubles as input from a file called "mandelinput.txt": Re0, Im0, and Re1. Im1 should be calculated as Im0 + (Re1-Re0) (i.e.,it should generate a square mandelbrot image).


The code I have is as follows, can anyone please tell me what the hell I am doing?

#include <fstream>
#include <iostream>

using namespace std;

const int maxiters = 500;
const int xpixels = 512;
const int ypixels = 512;


double red(int c){ 
	return ((c)%16)*64;          
}
double blue(int c){
	return 0;
}
double green(int c){
	return c;
}

int getCount(double a0, double b0){
	int count=0;
	double a=a0;
	double b=b0;
	double anext,bnext;

	while(a*a+b*b<4.0 && count < maxiters ){
		anext = a*a - b*b + a0;
		bnext = 2.0*a*b +b0;
		a=anext;
		b=bnext;
		count++;
	}

	return count;
}

int main(){
	ofstream outFile;
	ifstream inFile;
	outFile.open("mandeloutput.ppm");

	
	
	double x0, y0, x1,y1=0;
	double x,y,i,j,c;
	
	inFile.open("mandelinput.txt");
		if(!inFile)
			cout<<"file open error.\n";
		else{
			while(!inFile.eof())
				inFile>>x0>>y0>>x1;}

	 y1=y0+(x1-x0);

	 outFile << "P3\n" << xpixels << " " << ypixels << "\n255\n";

	 for(j=0;j<ypixels; ++j)
	 {
		 x=x0+(x1-x0)/xpixels*j;
	 
		 for(i=0;i<xpixels; ++i)
		 {
		 y=y0+(y1-x0)/ypixels*i;
	 
		c=getCount(x,y);
			if(c==maxiters)
				outFile<<"0 0 0";
			else
				outFile<<red(c)<<" ";
				outFile<<blue(c)<<" ";
				outFile<<green(c)<<" ";
		}
	 outFile<<endl;
	 }
	return 0;
}

[helios]

Could you post mandelinput.txt?

[2EURX9L8]

-2.0
1.0
-1.2

Ok so I must be reading it wrong from the file, cause even though it still dosent look like a mandelbrot, its at least square when I assign values to x0,y0 and x1.

[helios]

That region looks pretty much like that. It's not a particularly interesting region. Try

-3.0
-3.0
3.0

You did have a subtle bug in your code, though:

if(c==maxiters)
	outFile<<"0 0 0 "; // <- missing space screws up color
else{ // <- missing braces
	outFile<<saturate(red(c))<<" ";
	outFile<<saturate(blue(c))<<" ";
	outFile<<saturate(green(c))<<" ";
}

saturate() is simply this:

int saturate(double x){
	if (x<0)
		return 0;
	if (x>255)
		return 255;
	return (int)x;
}

PS: It's also worth noting that you're putting the real axis vertically. By convention, it goes horizontally, so you might want to change that.