Thanks for looking at this David, The "selection" isn't really there in my application; I added this later to the screen shots to show more clearly what was going on. For those reading along who don't want to download the screen shot, here's what's happening:
I print the string "abcabcabcabcabc" 25 times, each time with an extra period appended, like so: abcabcabcabcabc abcabcabcabcabc. abcabcabcabcabc.. abcabcabcabcabc... etc. The effect I'm seeing is that the "abcabcabcabcabc" part of the string doesn't have the same width when I draw the text via an intermediate CGLayer. The "abcabcabcabcabc" in the last line is a few pixels "tighter" than in the first line (and it's a gradual effect). I can understand that text rendering is (subtly) different depending on the context I'm drawing to, so I could understand that the "direct" version has different (sub-pixel) anti-aliasing and even (as a consequence) different spacing. (By the way, given your explanation I would expect the spacing differences in the "direct" version and not in the CGLayer version.) However, the point is that the spacing is inconsistent _within_ the same context. It sounds nit-picky, but in my "real" app the text is editable, and it is very noticeable that while typing, the characters to the left of the cursor "jitter around". I tried setting CGContextShouldAntialias and CGContextShouldSmoothFonts to NO (in all permutations) and the effect is still there. In case it matters, I am seeing the exact same behavior on an Intel MBP with 10.6 and on a PPC iBook G4 with 10.5. Thanks, Sander On Feb 5, 2010, at 9:06 PM, David Duncan wrote: > On Feb 5, 2010, at 7:46 AM, Sander Stoks wrote: > >> I want to draw rotated text, and I found out that the regular Cocoa Text >> drawing in that case looks surprisingly bad. I posted about this before, >> and got the suggestion of drawing to an offscreen bitmap instead, and >> rotating that. That works, but when I'm editing the text I see the text >> which is already there "jitter" on screen. I pruned this down to a minimal >> project which shows the problem. This can be downloaded at >> http://www.stoks.nl/TextTest.zip - it only contains a single NSView subclass >> which has selectable code paths (via an #if 0) for either drawing directly >> using NSLayoutManager's drawGlyphsForGlyphRange. This looks fine (as long >> as it's not rotated). The other path uses a CGLayer, sets the current >> NSGraphicsContext so it points to this layer, use drawGlyphsForGlyphRange >> again, and finally CGContextDrawLayerAtPoint to display the resulting text. >> >> As you can see in http://www.stoks.nl/TextCompared.png, the text drawn via >> the intermediate CGLayer "shrinks" its intra-glyph-spacing as the string >> gets longer. > > > Its hard to tell because your text is selected in your screen shot, but I > would guess that this has to do with subpixel antialiasing. By default your > text will be drawn without a background. When you draw directly into the > NSView however, there is an established background, that of the window, and > so the text can be blended into it with subpixel antialiasing. When you draw > to the CGLayer however, there is no such background, so the text is drawn > without. > > This typically manifests as the text not appearing as if it has the right > weight (appears thin or not bold enough), although it is harder to tell in > your case due to the selection area. If you see colored highlights when you > zoom in on the image in one but not the other, then it is the issue I'm > describing. > -- > David Duncan > Apple DTS Animation and Printing > > _______________________________________________ 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: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
