On May 5, 2012, at 1:12 PM, Peter Teeson wrote: > As to odd number of pixels I was under the impression that the parameters are > in points, > which are a unit of length* whereas pixels are related to hardware specs. > e.g. Line width is in points.
That’s right. But everything you draw is going to be mapped onto pixels by the time it’s onscreen. > So it is not the responsibility of the device driver to map points to pixels > in a device dependent way? It does that, but the results may not always be exactly what you want. :) The default behavior is to antialias, so if you stroke a one-point-wide black rectangle on integer point boundaries (assuming the usual 1pt==1px scaling) you will in fact get a two-pixel wide gray rectangle. Which is probably not what you wanted. This is because the edges are on pixel boundaries so the strokes are going halfway through the pixels on either side. The solution as I said is to add 0.5 to the coordinates so that the stroke edges fall on pixel boundaries. (IIRC there are some AppKit geometry utility functions that will adjust coordinate values to fit pixel boundaries in a resolution-independent way. I don’t remember their names offhand.) Someday every device will have retina-quality graphics and these details won’t matter, but currently they definitely do, especially for UI elements with thin horizontal and vertical lines. (And actually they may matter even on retina displays. These details of pixel rounding are definitely important at 300dpi on printers, which is why PostScript fonts are hinted — hinting consists almost entirely of moving edges of curves onto pixel boundaries. I remember from the old days that unhinted fonts on a 300dpi LaserWriter looked like shit. It turns out that even if your eye can’t distinguish individual pixels 1/300” across, it can easily tell the difference between a 1/300” and a 1/150” thick line.) —Jens _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) 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 arch...@mail-archive.com
