Question

 -(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
mouseSwiped = YES;

UITouch *touch = [touches anyObject];   
CGPoint currentPoint = [touch locationInView:scrollView];

//[self drawLine:lastPoint.x :lastPoint.y :currentPoint.x :currentPoint.y]; 
tempShapeLayer = nil;
CGMutablePathRef linePath = nil;
linePath = CGPathCreateMutable();
tempShapeLayer = [CAShapeLayer layer];

tempShapeLayer.lineWidth = 4.0f;
tempShapeLayer.lineCap = kCALineJoinMiter;
tempShapeLayer.strokeColor = [[UIColor redColor] CGColor];


CGPathMoveToPoint(linePath, NULL, lastPoint.x, lastPoint.y);
CGPathAddLineToPoint(linePath, NULL, currentPoint.x, currentPoint.y);


tempShapeLayer.path = linePath;
CGPathRelease(linePath);

[scrollView.layer addSublayer:tempShapeLayer];

lastPoint = currentPoint;

}

i am drawing line by this code . but i want this line remain straight. means when i move my touch the line should not become smooth.line will be remain straight.

i think i have to do something like

  if (currentPoint.x > lastPoint.x){        
    currentPoint.y = lastPoint.y;
} 
else if (currentPoint.x < lastPoint.x) {
    currentPoint.x = lastPoint.x;
}

Answer 1

if you are moving subpixels you will get unwanted antialiasing. I suggest floor/ceil to a non float. This obviously gets more complicated when working with retina vs non retina.