Setting a line width of 0 draws a 1-pixel wide line at the
resolution of the device it draws to, so on screen, that's 1/72 of
an inch (approx) on a printer 1/600 inch, say. It's a useful way to
isolate drawing from any CTM scaling. This is handy for drawing a
selection rect outline on top of a zoomed image where you don't want
the selection itself to be scaled up (among many other uses). So
yes, I'd say it works - and Quartz most definitely does draw strokes
with a line width of 0.
No, Quartz 2D does not draw zero width strokes.
If you use NSBezierPath and supply a stroke width of 0 then Cocoa will
fudge the stroke width on your behalf and come up with something that
approximates a single pixel line, but Quartz 2D itself will not draw a
0 pixel wide line. You can try it yourself:
- (void) drawRect: (NSRect) rectToDraw
{
// This, of course, will draw
NSBezierPath *bezierPath = [NSBezierPath bezierPathWithRect:
NSMakeRect(20, 20, 150, 150)];
[bezierPath setLineWidth: 1];
[[NSColor blueColor] set];
[bezierPath stroke];
// This also will draw because Cocoa is nice and fudges the
underlying Quartz drawing for you
bezierPath = [NSBezierPath bezierPathWithRect: NSMakeRect(10, 10,
200, 200)];
[bezierPath setLineWidth: 0];
[[NSColor redColor] set];
[bezierPath stroke];
// This will not draw anything because Quartz does not draw zero
width lines.
CGContextRef cgContext = (CGContextRef) [[NSGraphicsContext
currentContext] graphicsPort];
CGContextSetLineWidth(cgContext, 0);
CGContextSetRGBStrokeColor(cgContext, 0.0, 1.0, 0.0, 1.0);
CGContextAddRect(cgContext, CGRectMake(5, 5, 150, 150));
CGContextStrokePath(cgContext);
}
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