Draw Graph curves with UIBezierPath

Question

I'm drawing a graph in my application. My problem is that I want to draw line joining vertex points as curves. Currently I'm drawing them with UIBezierPath's function addLineToPoint:. I want to draw them as curves. I'm well aware that UIBezierPath has following two functions to support this feature.

Cubic curve:addCurveToPoint:controlPoint1:controlPoint2: Quadratic curve:addQuadCurveToPoint:controlPoint:

But problem is that I don't have control points. All i have is two end points. Neither I found a method/formula to determine control points. Can anyone help me here? I will appreciate if someone can suggest some alternative...

Answer 1

SO I found a work around based on @Fogmeister's answer.

    UIBezierPath *path = [UIBezierPath bezierPath];
    [path setLineWidth:3.0];
    [path setLineCapStyle:kCGLineCapRound];
    [path setLineJoinStyle:kCGLineJoinRound];

    // actualPoints are my points array stored as NSValue

    NSValue *value = [actualPoints objectAtIndex:0];
    CGPoint p1 = [value CGPointValue];
    [path moveToPoint:p1];

    for (int k=1; k<[actualPoints count];k++) {

        NSValue *value = [actualPoints objectAtIndex:k];
        CGPoint p2 = [value CGPointValue];

        CGPoint centerPoint = CGPointMake((p1.x+p2.x)/2, (p1.y+p2.y)/2);

        // See if your curve is decreasing or increasing
        // You can optimize it further by finding point on normal of line passing through midpoint 

        if (p1.y<p2.y) {
             centerPoint = CGPointMake(centerPoint.x, centerPoint.y+(abs(p2.y-centerPoint.y)));
        }else if(p1.y>p2.y){
             centerPoint = CGPointMake(centerPoint.x, centerPoint.y-(abs(p2.y-centerPoint.y)));
        }

        [path addQuadCurveToPoint:p2 controlPoint:centerPoint];
        p1 = p2;
    }

    [path stroke];