On 25.08.2012, at 18:05, Andy Lee <[email protected]> wrote: > hard to speculate since I don't know what this method is used for.
It's for resolution independence and sharp line drawing. Quartz coordinates run *between* pixels, so if you draw a 1px black line from 10,10 to 100,10, you get a 2-pixel-wide 50% grey line (because each pixel should be half white and half black, but since one can't do half pixels, it just averages the two values). To fix this, before resolution independence, you just added 0.5 to the coordinate, which made it run through the middle of each pixel. But with resolution independence, you could (theoretically, if not yet in practice) have a 3x scale factor, in which case adding 0.5 would actually cause inaccurate drawing even though you could just draw that middle line. So they added this call, which you feed resolution-independent point coordinates and it nudges them depending on how many pixels your current context uses per point, to give you a sharp line (at the loss of a bit of precision, but only a little, and only when actually needed). Cheers, -- Uli Kusterer "The Witnesses of TeachText are everywhere..." http://www.masters-of-the-void.com _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
