Thread: Bresenham Circle Algorithm

Does anyone have experience with this algo.. i can't seem to get it working right (i converted the code i found on gamedev from pascal to c++)?

Code:

	
PHP Code:
	

    int d,mx,my;

    d = 3 - (2*radius);
    mx = 0;
    my = radius;

    while(my != mx)
    {
        DrawPixel(surface,x+mx,y+my,color);
        DrawPixel(surface,x+mx,y-my,color);
        DrawPixel(surface,x-mx,y+my,color);
        DrawPixel(surface,x-mx,y-my,color);
        DrawPixel(surface,x+my,y+mx,color);
        DrawPixel(surface,x+my,y-mx,color);
        DrawPixel(surface,x-my,y+mx,color);
        DrawPixel(surface,x-my,y-mx,color);

        if(d < 0)
            d += (4*mx)+6;    
        else
        {
            d += 4*(mx-my) + 10;
            my--;
        }
    } 

edit: It is drawing a + sign rather than an O.. I'm trying to figure this one out but so far no luck.

I don't remember if it was Bresenham's or another one, but I got it to work with DirectDraw. I'll try and find it.

Here's the algorithm I used: (it's almost actual code so you should be able to modify it to what you need)

Code:

int x_center;  // the center of the circle
int y_center;

int x;  // used for the algorithm to draw points on the border
int y;

int radius;

int r2 = radius * radius; // the radius sqaured

PutPixel( x_center, y_center + radius );
PutPixel( x_center, y_center - radius );
PutPixel( x_center + radius, y_center );
PutPixel( x_center - radius, y_center );

x = 1;
y = (int)( sqrt( r2 - 1 ) + 0.5 );

while( x < y ) {

  PutPixel( x_center + x, y_center + y );
  PutPixel( x_center + x, y_center - y );
  PutPixel( x_center - x, y_center + y );
  PutPixel( x_center - x, y_center - y );
  PutPixel( x_center + y, y_center + x );
  PutPixel( x_center + y, y_center - x );
  PutPixel( x_center - y, y_center + x );
  PutPixel( x_center - y, y_center - x );

  ++x;
  y = (int)( sqrt( r2 - x * x ) + 0.5 );
}
if (x == y) {

  PutPixel( x_center + x, y_center + y );
  PutPixel( x_center + x, y_center - y );
  PutPixel( x_center - x, y_center + y );
  PutPixel( x_center - x, y_center - y );
}