Circumscribed Circle

MyView.m

#import <Cocoa/Cocoa.h>
@interface MyView : NSView
@end
@implementation MyView
double len(NSPoint p){return sqrt(p.x*p.x+p.y*p.y);}
NSRect bboxOfCircumscribedCircle(NSPoint p0, NSPoint p1, NSPoint p2) {
    double a= len(NSMakePoint(p2.x-p1.x, p2.y-p1.y));
    double b= len(NSMakePoint(p2.x-p0.x, p2.y-p0.y));
    double c= len(NSMakePoint(p1.x-p0.x, p1.y-p0.y));
    double Ca=a*a*(b*b+c*c-a*a);
    double Cb=b*b*(c*c+a*a-b*b);
    double Cc=c*c*(a*a+b*b-c*c);
    double tmp= Ca+Cb+Cc;
    if (tmp<=0.0) return NSZeroRect;
    double S= 1.0/4.0*sqrt(tmp);
    double R= a*b*c/4/S;
    double CS= 1.0/16.0/S/S;
    NSPoint O= NSMakePoint(CS*(Ca*p0.x+Cb*p1.x+Cc*p2.x),CS*(Ca*p0.y+Cb*p1.y+Cc*p2.y));
    return NSMakeRect(O.x-R, O.y-R, 2*R, 2*R);
}
NSRect handle(NSPoint p){return NSMakeRect(p.x-2, p.y-2, 4, 4);}
NSPoint midPoint(NSRect r){return NSMakePoint(NSMidX(r), NSMidY(r));}
- (void)drawRect:(NSRect)dirtyRect {
    [[NSColor whiteColor] set];
    NSRectFill(dirtyRect);
    for(NSUInteger x=50;x<200;x+=25) {
        NSPoint p0= NSMakePoint(100, 300);
        NSPoint p1= NSMakePoint(x, x);
        NSPoint p2= NSMakePoint(300, 100);
        [[NSColor blackColor] set];
        NSFrameRect(handle(p0));
        NSFrameRect(handle(p1));
        NSFrameRect(handle(p2));
        NSRect rect= bboxOfCircumscribedCircle(p0, p1, p2);
        NSFrameRect(rect);
        [[NSColor redColor] set];
        NSRectFill(handle(midPoint(rect)));
        [[NSBezierPath bezierPathWithOvalInRect:rect] stroke];
    }
}
@end