Core graphics drag over pixels instead of points - objective-c

Question

Ok, I haven't found it anywhere. What should I do if i want to draw with core graphics per pixel? Like… I want to draw a line to pixels (45,61) and than (46,63) instead of drawing to point (23,31) or something like that. So what should I do in this case?
Should I use something like:
CGContextAddLineToPoint(context,22.5,30.5);
CGContextAddLineToPoint(context,23,31.5);
Or there is some better way?
I know about contentScaleFactor but should I use it as (when plotting some function for example):
for(int x=bounds.origin.x; x<=bounds.origin.x+bounds.size.width*[self contentScaleFactor]; i++)
CGContextAddLineToPoint(context,x/[self contentScaleFactor],y(x/[self contentScaleFactor]));
I know that the example code is not superb, but I think you'll get the idea.
I'll be vey thankful for help because I'm a bit confused with all this scale factor stuff.

Answer 1

Sounds like you are doing the Assignment3 from the iOS uTunes Stanford Course? :)
I think you are on the right track, as my implementation looks very similar:
for(int x=self.bounds.origin.x; x<=self.bounds.origin.x + (self.bounds.size.width * self.contentScaleFactor); x++) {
// get the scaled X Value to ask dataSource
CGFloat axeX = (x/self.contentScaleFactor - self.origin.x) / self.scale;
// using axeX here for testing, which draws a x=y graph
// replace axeX with the dataSource Y-Point calculation
CGFloat axeY = -1 * ((axeX * self.scale) + self.origin.y);
if (x == self.bounds.origin.x) {
CGContextMoveToPoint(context, x/self.contentScaleFactor, axeY);
} else {
CGContextAddLineToPoint(context, x/self.contentScaleFactor, axeY);
}
}
Tested on iOS-Sim iPhone4 (contentScaleFactor 1.0) + iPhone4S Device (contentScaleFactor 2.0).
Would be happy about possible improvements from other readers, because I am still learning.