Confusing lag situation - UIBezierPath re-draw going too slaw - ios

Question

I've got a "SLATE2" tablet that allows me to write on a tablet with a special pen and interact with my own app. I'm having some trouble though, and I don't think it's a problem with hardware.
- (void)touchesBegan: (CGPoint)point
{
[path moveToPoint:point];
}
- (void)touchesMoved: (CGPoint)point
{
[path addLineToPoint: point]; // (4)
[Newpath appendPath: path];
pathTwo = [UIBezierPath bezierPath];
pathTwo = [UIBezierPath bezierPathWithCGPath:Newpath.CGPath];
pathTwo = [pathTwo fitInto: self.bounds];
[self setNeedsDisplay];
}
- (void)touchesEnded: (CGPoint)point
{
pathTwo = [UIBezierPath bezierPath];
pathTwo = [UIBezierPath bezierPathWithCGPath:Newpath.CGPath];
pathTwo = [pathTwo fitInto: self.bounds];
[path removeAllPoints];
[self setNeedsDisplay];
}
- (void)drawRect:(CGRect)rect {
[[UIColor whiteColor] setStroke];
[pathTwo stroke];
return;
}
The drawing to the UIView screen is far too slow. I'm looking at the console and the events being raised by the actual tablet are at almost lightspeed. If there is a better way to draw on this UIView faster please show me.
I've dscovered the issue. fitInto is called so frequently and pathTwo is re-drawn every time. I need fitInto to be called everytime theres a new part of the pad that's drawn on to scale how much is shown.
I tried turning off anti-aliasing but that didn't work.
fitInto works like so...
imagine the screen of the iphone
and if you were to draw on a tablet, a square tablet, at the bottom, say a circle, if you were to draw a circle, it would just zoom in on the iphone screen as its the only drawing on the tablet. if you draw at the top of the tablet, the circle at the bottom is now shown to scale of the entire tablet because of the two opposing ends. i don't think this function could be made any faster... but let's try!
func fit(into:CGRect) -> Self {
let bounds = self.cgPath.boundingBox
let sw = into.size.width/bounds.width
let sh = into.size.height/bounds.height
let factor = min (5, min(sw, max(sh, 0.0)))
return scale(x: factor, y: factor, into: into)
}
and here is scale
func scale(x:CGFloat, y:CGFloat, into: CGRect? = nil) -> Self{
var transform = CGAffineTransform(scaleX: x, y: y)
if into != nil {
transform = transform.concatenating(CGAffineTransform(translationX: into!.midX - self.cgPath.boundingBox.midX, y: into!.midY - self.cgPath.boundingBox.midY))
}
let _ = applyCentered(transform: transform)
return self
}

Answer 1

Have you checked how many points are actually in your path? I don't think you want to draw your CGPath pixel by pixel. Instead you should only add a segment when the distance exceeds a certain threshold. You can also simplify the path by drawing curves through the points instead of drawing line segments. See this primer on bezier curves.
EDIT: The Ray Wenderlich sample app looks like its actually doing the same thing, adding points in TouchedMoved. However in touchesEnded they rasterize the curve into a bitmap. I'm not so sure that that will help your case though because it looks like you are deleting all of the points in touchesEnded. I would still look at their code and see if you have any other points that could be a bottle neck.

Answer 2

What effect are you after? Are you trying to let the user trace lines and curves with the pen, or dots if they tap?
The simple fact is that iOS is not fast enough to track the user's pen/finger strokes point-by-point. Instead, you want to collect a series of points and create a UIBezierPath that connects those points with line segments. That will give you something pretty close to what you want. However, if the user traces fast, that will lag behind as well.