On 20/03/2009, at 7:39 AM, John Reppy wrote:
I'm building a viewer for event logs that needs to support a wide
range
of scales (say from seconds/inch to nanoseconds/inch). I've got a
custom
subclass of NSView for displaying this information, which I want to
embed
in an NSScrollView. The problem that I'm faced with is that the
floating-point
coordinates used by Cocoa do not have enough precision at full
magnification.
I'm guessing that the best solution is to subclass NSScrollView to
track the
visible rectangle's origin using doubles, but I'm not sure which
NSScrollView
methods I should be overriding. Also, do I need to override
NSClipView too?
Any pointers or suggestions would be appreciated.
Double's are not going to help.
The drawing coordinates are floats. Even if you could persuade
NSScrollView to position your view to double precision, it will get
truncated to single precision for display. You'd have to rewrite all
of Quartz at 64 bit precision to see any benefit.
However, all is not lost.
A float easily exceeds a 10^9 range, so you merely need to scale
everything upwards. e.g. define 1nS to be, say, 10 points, then draw
everything else on that basis. You can then scale the whole view to
show the timeline scale you need. Scaling the view itself is trivial,
see -scaleUnitSquareToSize:
-Graham
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