NSBezierPath to NSImage with subpixel rendering

FROM : Gregory 'guardian' Pakosz
DATE : Wed Jan 09 12:40:38 2008

Hello,

I am trying to stroke a bezier path into an off-screen buffer.

in the -initWithFrame: method of my custom view, i created an NSImage
instance

image = [[NSImage alloc] initWithSize:frameRect.size];

i created an NSBezierPath and added stuff:

path = [[NSBezierPath alloc] init];
[path *drawStuff*]; // drawing here

then, still inside -initWithFrame: i stroke the path into the image:

[image lockFocus];
[[NScolor whiteColor] set];
[NSBezierPath fillRect:[frameRect]];

[[NScolor blackColor] set];
[path stroke];
[image unlockFocus];

so by now, as part of my custom view initialization the NSImage instance
is supposed to contain my stroked path.

afterwards, in -drawRect: i just do:

[image drawInRect: rect
          fromRect: rect
        operation: NSCompositeCopy
          fraction: 1.0];

by doing that, i don't benefit from subpixel precision :(
the problem is that it seems that subpixel rendering wasn't applied when
rendering into the NSImage, although i painted a white background (by
filling a white rect).

however, if i move the path stroking code into drawRect:

- (void)drawRect:(NSRect)rect
{
  [image lockFocus];
  [[NScolor whiteColor] set];
  [NSBezierPath fillRect:[frameRect]];

  [path stroke];
  [image unlockFocus];

  [image drawInRect: rect
            fromRect: rect
          operation: NSCompositeCopy
            fraction: 1.0];
}

then i get subpixel precision.

so, what's the proper way to achieve offscreen antialising + subpixel
precision in an NSImage that has a background ??? (
http://michelf.com/weblog/2006/subpixel-antialiasing-achilles-heel/
seems to explain why it's impossible to do it with transparent backgrounds)

i guess this is related to graphic contexts but i'm just learning cocoa,
please help :)

regards,
g.