Thread: Drawing circle into a bitmap file

I wrote a c++ program in order to draw some shapes bit by bit. But I have difficulties in drawing circle. I couldn't give it's original shape. I think about finding any point on a circle by using the formulas,but i have two unknowns.

for ex: r^2=(x-a)^2-(y-b)^2

where:
x and y are the x,y coordinates for any point on the circle.
a and b are the x,y coordinates for the center of the circle.
r is the radius of the circle

I give the center cordinates,i have the radius... But there are two variables (x,y) which is unknown.How can i get points.

Here is the code that I work for other shapes:

Code:

#include <iostream>
#include <fstream>

class BMP
{
public:
	unsigned char header[1078];
	unsigned char data[640][480];
	BMP()
	{
		for(int i = 0; i<1078; i++)
			header[i] = 0;

		header[0] = 'B';
		header[1] = 'M';
		unsigned char* p = &header[2];	
		*(int*)(p) = 0x4b436; 
		p = &header[6]; 
		*(int*)(p) = 0x0;
		p = &header[10]; 
		*(int*)(p) = 0x436;
		p = &header[14]; 
		*(int*)(p) = 0x28;
		p = &header[18]; 
		*(int*)(p) = 0x280;
		p = &header[22]; 
		*(int*)(p) = 0x1e0;
		p = &header[26]; 
		*(unsigned short*)(p) = 0x1;
		p = &header[28]; 
		*(unsigned short*)(p) = 0x8;
		p = &header[30]; 
		*(int*)(p) = 0x0;
		p = &header[34]; 
		*(int*)(p) = 0x4b000;
		p = &header[38]; 
		*(int*)(p) = 0x0;
		p = &header[42]; 
		*(int*)(p) = 0x0;
		p = &header[46]; 
		*(int*)(p) = 0x0;
		p = &header[50]; 
		*(int*)(p) = 0x0;

		p = &header[54];
		*(int*)(p) = 0x0;
		p = &header[58];
		*(int*)(p) = 0x800000;
		p = &header[62];
		*(int*)(p) = 0x8000;
		p = &header[66];
		*(int*)(p) = 0x808000;
		p = &header[70];
		*(int*)(p) = 0x80;
		p = &header[74];
		*(int*)(p) = 0x800080;
		p = &header[78];
		*(int*)(p) = 0x8080;
		p = &header[82];
		*(int*)(p) = 0x808080;
		p = &header[86];
		*(int*)(p) = 0xC0C0C0;
		p = &header[90];
		*(int*)(p) = 0xFF00000;
		p = &header[94];
		*(int*)(p) = 0xFF00;
		p = &header[98];
		*(int*)(p) = 0xFFFF00;
		p = &header[102];
		*(int*)(p) = 0xFF;
		p = &header[106];
		*(int*)(p) = 0xFF00FF;
		p = &header[110];
		*(int*)(p) = 0xFFFF;
		p = &header[114];
		*(int*)(p) = 0xFFFFFF;

		
		for(int i= 0; i<640; i++)
			for(int j= 0; j<480; j++)
				data[i][j] = 15;
	}

	void save(const std::string str="");

	void line(int x1, int y, int length, int color)
	{
		for(int i=x1;i<x1+length;i++)
			data[i][y] =  color;
	}

	void point(int x, int y, int color)
	{
		data[x][y] = color;
	}
	
	void rectangle(int x1, int x2, int y1, int y2,int color)
	{
		for(int i=x1;i<x2;i++)
			data[i][y1] =  color;
				
		for(int y=y1;y<y2;y++)
			data[x1][y] =  color;

		for(int i=x1;i<x2;i++)
			data[i][y2] =  color;

		for(int y=y1;y<y2;y++)
			data[x2][y] =  color;
					
	}
	void square(int x1, int y1, int length,int color)
	{
		for(int i=x1;i<x1+length;i++)
			data[i][y1] =  color;
				
		for(int y=y1;y<y1+length;y++)
			data[x1][y] =  color;

		for(int i=x1;i<x1+length;i++)
			data[i][y1+length] =  color;

		for(int y=y1;y<y1+length;y++)
			data[x1+length][y] =  color;
	
	}
	
};

void BMP::save(const std::string str)
{
	int i = 0;

	std::ofstream f(str.c_str());

	for(i = 0; i<1078; i++)
		f<<header[i];

	for(int i= 0; i<480; i++)
			for(int j= 0; j<640; j++)
				f<<data[j][i];

	f.close();
}

int main()
{
	BMP bitmap;

	bitmap.line(100, 150, 150, 12);
	bitmap.rectangle(200, 400, 200, 300,12);
	bitmap.square(300, 50, 100,1);
	bitmap.save("renk.bmp");

	return 0;
}

Code:

r^2 = (x - a)^2 - (y - b)^2

(y - b)^2 = (x - a)^2 - r^2

y - b = +- ((x - a)^2 - r^2)^0.5

y = b +- ((x - a)^2 - r^2)^0.5

Then you can plug in points for x from r to -r (x is not unknown, it has a domain that you plug in stuff for). This is not a very good algorithm though, and the circle will be splotchy. Google circle drawing algorithms.