On 28/04/2009, at 3:54 AM, Tobias Zimmerman wrote:
I think that, at best, the documentation is ambiguous. It would be
clearer
specifically saying "If no value was set explicitly for the
receiver, this
method [lineWidth] returns the default line width ->at the time the
receiver
was created<-" I may file a RADR on that.
Well, it didn't seem too ambiguous to me - but then again additional
clarification wouldn't hurt.
It is further confusing because the actual effect of the lineWidth
property
is dependent on the view in which the drawing takes place -- that
is, a line
width of "1.0" in one view will not necessarily appear the same
width in a
separate view that has a different dot-pitch, pixel ratio, etc.
That's not the case. The whole point of Quartz is that it is
resolution independent. 1.0 points always means 1.0 points, and when
that's rasterized it will set as many pixels as necessary on the
device it's drawing to. Of course if the resolution is such that the
smallest pixel is effectively 2 points, Quartz can only fake it by
drawing the 2pt pixel at half brightness. This happens when you use a
line width of, say 0.5, and the smallest pixel is 1.0 points. However
the appearance of the line will be consistent, within reason (very
coarse resolutions obviously cause problems with this approach, but
these days 72dpi is definitely a minimum). Don't confuse points and
pixels. While by default without scaling, on screen there is a 1:1
correspondence between them they are completely independent.
The only exception to this is when you specify a line width of 0 with
NSBezierPath - that will be resolution dependent but it's a special
case, and doesn't apply to the CGPath functions. If your aim is to
always draw a 1-pixel wide line no matter what the target resolution
is, a line width of 0 will do that. If your aim is to always draw a 2-
pixel line, you'd have to calculate the necessary line width knowing
the resolution of the device and scaling appropriately, as there's no
built-in way to force this kind of resolution dependence.
If you want to use a fixed resolution regardless, you could create a
suitable bitmap and draw into that, then draw that to the target
device as needed (and turn off anti-aliasing for that genuine Windows
3.1 look).
Where a drawn line width will also appear differently is when a view
is scaled (i.e. the view context has a scaling transform in force),
but then you'd expect that I would have thought.
--Graham
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