Smoothed drawing.

SmoothedBIView.mm

#import "SmoothedBIView.h"
#import "TouchProfiler.h"

@implementation SmoothedBIView
{
    UIBezierPath *path;
    UIImage *incrementalImage;
    CGPoint pts[5]; // we now need to keep track of the four points of a Bezier segment and the first control point of the next segment
    uint ctr;
    TouchProfiler *_profiler;
}
//- (id)initWithCoder:(NSCoder *)aDecoder
//{
//    if (self = [super initWithCoder:aDecoder])
//    {
//        [self setMultipleTouchEnabled:NO];
//        [self setBackgroundColor:[UIColor whiteColor]];
//        path = [UIBezierPath bezierPath];
//        [path setLineWidth:2.0];
//    }
//    return self;
//}
- (id)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame])
    {
        _profiler = new TouchProfiler(); // release
        [self setMultipleTouchEnabled:NO];
        [self setBackgroundColor:[UIColor whiteColor]];
        path = [UIBezierPath bezierPath];
        [path setLineWidth:2.0];
    }
    return self;
}
/*- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        [self setMultipleTouchEnabled:NO];
        path = [UIBezierPath bezierPath];
        [path setLineWidth:2.0];
    }
    return self;
}*/
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
    [incrementalImage drawInRect:rect];
    [path stroke];
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    _profiler->addPoint();
    ctr = 0;
    UITouch *touch = [touches anyObject];
    pts[0] = [touch locationInView:self];
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    _profiler->addPoint();
    UITouch *touch = [touches anyObject];
    CGPoint p = [touch locationInView:self];
    ctr++;
    pts[ctr] = p;
    if (ctr == 4)
    {
        pts[3] = CGPointMake((pts[2].x + pts[4].x)/2.0, (pts[2].y + pts[4].y)/2.0); // move the endpoint to the middle of the line joining the second control point of the first Bezier segment and the first control point of the second Bezier segment
        [path moveToPoint:pts[0]];
        [path addCurveToPoint:pts[3] controlPoint1:pts[1] controlPoint2:pts[2]]; // add a cubic Bezier from pt[0] to pt[3], with control points pt[1] and pt[2]
        [self setNeedsDisplay];
        // replace points and get ready to handle the next segment
        pts[0] = pts[3];
        pts[1] = pts[4];
        ctr = 1;
    }
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    _profiler->addEnd();
    [self drawBitmap];
    [self setNeedsDisplay];
    [path removeAllPoints];
    ctr = 0;
}
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{
    [self touchesEnded:touches withEvent:event];
}
- (void)drawBitmap
{
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, YES, 0.0);
    if (!incrementalImage) // first time; paint background white
    {
        UIBezierPath *rectpath = [UIBezierPath bezierPathWithRect:self.bounds];
        [[UIColor whiteColor] setFill];
        [rectpath fill];
    }
    [incrementalImage drawAtPoint:CGPointZero];
    [[UIColor blackColor] setStroke];
    [path stroke];
    incrementalImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
}
@end