The Bezier curve algorithm in objective-c needs to be tuned

I set up a quick Bezier curve algorithm in objective-c , which seemed to solve my problems. I ask this new question, because I think that it is quite different, and does not repeat the old one.

I have something that looks like a working Bezier algorithm, but NSBezierPaththere are some serious problems compared to the embedded version . It seems that some types of curves are very distorted.

You can see the differences from the above image, the red line is my function, and the lighter color is the built-in version. I do not expect and disagree, pixel for pixel, but as you can see, the red lines from time to time go off course.

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- (void)MakeBezier
{
    int x1 = [self getMegaNumber:2];
    int y1 = self.frame.size.height - [self getMegaNumber:2];
    int x2 = [self getMegaNumber:2];
    int y2 = self.frame.size.height - [self getMegaNumber:2];
    int x3 = [self getMegaNumber:2];
    int y3 = self.frame.size.height - [self getMegaNumber:2];
    int x4 = [self getMegaNumber:2];
    int y4 = self.frame.size.height - [self getMegaNumber:2];
    int cnt = [self getMegaNumber:2]; 

    NSBezierPath *bezierPath = [[NSBezierPath alloc] init];
    [bezierPath setLineWidth:1.0f];
    [bezierPath moveToPoint:NSMakePoint(x1, y1)];
    [bezierPath curveToPoint:NSMakePoint(x4, y4) controlPoint1:NSMakePoint(x2, y2) controlPoint2:NSMakePoint(x3, y3)];

    // Draw path to image with build in NSBezierPath
    [self drawPath:bezierPath fill:NO];

    // Draw path with custom algorithm    
    [self drawBezierFrom:NSMakePoint(x1, y1) to:NSMakePoint(x4, y4) controlA:NSMakePoint(x2, y2) controlB:NSMakePoint(x3, y3) sections:cnt color:4];
}

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- (void)drawBezierFrom:(NSPoint)from to:(NSPoint)to controlA:(NSPoint)a controlB:(NSPoint)b sections:(NSUInteger)cnt color:(NSUInteger)color
{
    float qx, qy;
    float q1, q2, q3, q4;
    int lastx = - 1, lasty;
    int plotx, ploty;
    float t = 0.0;

    while (t <= 1)
    {
        q1 = t*t*t*-1 + t*t*3 + t*-3 + 1;
        q2 = t*t*t*3 + t*t*-6 + t*3;
        q3 = t*t*t*-3 + t*t*3;
        q4 = t*t*t;

        qx = q1*from.x + q2*a.x + q3*to.x + q4*b.x;
        qy = q1*from.y + q2*a.y + q3*to.y + q4*b.y;

        plotx = round(qx);
        ploty = round(qy);

        if (lastx != -1)
            [self drawLineFrom:NSMakePoint(lastx, lasty) to:NSMakePoint(plotx, ploty) color:color];
        else
            [self drawLineFrom:NSMakePoint(from.x, from.y) to:NSMakePoint(plotx, ploty) color:color];

        lastx = plotx;
        lasty = ploty;
        t = t + (1.0/(cnt + 0.0f));
    }
    [self drawLineFrom:NSMakePoint(lastx, lasty) to:NSMakePoint(to.x, to.y) color:color];
}

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