iOS DrawRect code optimisation - ios

Question

Most of the time the code below works correctly and draws paths based upon the user's gestures. However, when the app initially launches the drawRect method isn't able to keep pace with the pan gesture, meaning that the pan gesture is sometimes called multiple times before drawrect is able to draw. This results in a space where the path should be drawn. How could I improve this please?
- (void)pan:(UIPanGestureRecognizer *)pan
{
if (pan.state == UIGestureRecognizerStateChanged)
{
inputPathCounter++;
CGPoint velocity = [pan velocityInView:self];
previousPoint2 = previousPoint1;
previousPoint1 = currentPoint;
currentPoint = [pan locationInView:self];
float velocityMagnitude = sqrtf(velocity.x * velocity.x + velocity.y * velocity.y);
float clampedVelocityMagnitude = clamp(VELOCITY_CLAMP_MIN, VELOCITY_CLAMP_MAX, velocityMagnitude);
float normalizedVelocity = (clampedVelocityMagnitude - VELOCITY_CLAMP_MIN) / (VELOCITY_CLAMP_MAX - VELOCITY_CLAMP_MIN);
float lowPassFilterAlpha = STROKE_WIDTH_SMOOTHING;
float newThickness = (STROKE_WIDTH_MAX - STROKE_WIDTH_MIN) * normalizedVelocity + STROKE_WIDTH_MIN;
self.lineWidth = self.lineWidth * lowPassFilterAlpha + newThickness * (1 - lowPassFilterAlpha);
CGPoint mid1 = midPoint(previousPoint1, previousPoint2);
CGPoint mid2 = midPoint(currentPoint, previousPoint1);
CGMutablePathRef subpath = CGPathCreateMutable();
CGPathMoveToPoint(subpath, NULL, mid1.x, mid1.y);
CGPathAddQuadCurveToPoint(subpath, NULL, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y);
CGRect drawBounds = CGPathGetBoundingBox(subpath);
path = [[Path alloc] init];
path.width = self.lineWidth;
[self selectedColor];
path.bezierPath = [UIBezierPath bezierPathWithCGPath:subpath];
path.num = inputPathCounter;
CGPathRelease(subpath);
CGRect drawBox = drawBounds;
drawBox.origin.x -= self.lineWidth * 2.0;
drawBox.origin.y -= self.lineWidth * 2.0;
drawBox.size.width += self.lineWidth * 4.0;
drawBox.size.height += self.lineWidth * 4.0;
[self setNeedsDisplayInRect:drawBox];
}
else if (pan.state == UIGestureRecognizerStateEnded | pan.state == UIGestureRecognizerStateCancelled)
{
[self saveImage];
self.lineWidth = STROKE_WIDTH_MIN;
}
}
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
if(layer == nil)
{
//NSLog(#"reload layer");
layer = CGLayerCreateWithContext(context, bounds.size, NULL);
layerContext = CGLayerGetContext(layer);
CGContextScaleCTM(layerContext, scale, scale);
viewRect = CGRectMake(0, 0, self.bounds.size.width, self.bounds.size.height);
//NSLog(#"viewrect %f %f",viewRect.size.width, viewRect.size.height);
CGContextSaveGState(layerContext);
UIGraphicsBeginImageContext (viewRect.size);
CGContextTranslateCTM(layerContext, 0, self.image.size.height/scale);
CGContextScaleCTM(layerContext, 1.0, -1.0);
CGContextDrawImage(layerContext, viewRect, self.image.CGImage);
UIGraphicsEndImageContext();
CGContextRestoreGState(layerContext);
}
UIBezierPath *bezierPath = path.bezierPath;
CGContextAddPath(layerContext, bezierPath.CGPath);
CGContextSetLineWidth(layerContext, path.width);
CGContextSetStrokeColorWithColor(layerContext, path.color.CGColor);
CGContextSetLineCap(layerContext, kCGLineCapRound);
CGContextStrokePath(layerContext);
CGContextDrawLayerInRect(context, viewRect, layer);
}