[Drawkit] Scaling issues

[Brad Larson]

I was able to finish the file import for our XML-based pattern file  
format and tried out loading a few files.  I ran into some issues with  
grid and drawing scaling that we started to touch on earlier.

Our pattern files typically have a large dynamic range.  That is, we  
draw things out in microns, but the structures they make might be  
centimeters across.  This causes a problem with scaling, because we  
either have to start with small units and zoom way in to deal with  
fine features or start with larger units and zoom way out to see the  
whole pattern.

I tried setting the units to match the true dimensions of the objects  
we're drawing using

[currentDrawing setDrawingUnits:@"Microns"  
unitToPointsConversionFactor:(kGCGridDrawingLayerMetricInterval /  
10000)];
DKGridLayer* grid = [[DKGridLayer alloc] init];
[grid setSpan:(kGCGridDrawingLayerMetricInterval/100)  
unitToPointsConversionFactor:(kGCGridDrawingLayerMetricInterval /  
10000) measurementSystem:kGCMetricDrawingGrid drawingUnits:@"Microns"  
divisions:10 majors:2 rulerSteps:2];

and that created a really tiny grid and really tiny structures on  
load, because they were displayed at their real size.  That's not a  
problem, but when you zoom in, because everything is just scaled  
proportionally, the grid lines are so large that there's no white  
space in between.  Also, the object handles take up nearly a quarter  
of the screen and are unusable as a result.

Then I ignored the real dimensions and said that 1 micron equals one  
point

[currentDrawing setDrawingUnits:@"Microns"  
unitToPointsConversionFactor:1];
DKGridLayer* grid = [[DKGridLayer alloc] init];
[grid setSpan:(1 * 100) unitToPointsConversionFactor:1  
measurementSystem:kGCMetricDrawingGrid drawingUnits:@"Microns"  
divisions:10 majors:2 rulerSteps:2];

and that created larger features, but in order to see the whole  
pattern I needed to zoom out quite a bit.  I ran into a problem there  
because I hit the GCZoomView's minimumScale and it wouldn't let me  
zoom out any more.  Why are there minimum and maximum zoom scales?   
They don't seem to serve a purpose.  I tried subclassing DKDrawingView  
to remove them in my subclass, but ran into a "-[NSRulerMarker  
initWithRulerView:markerLocation:image:imageOrigin:]: no image given.   
NSRulerMarkers must have an image." exception when trying to use my  
subclass for the DKDrawingView in IB.  I just gave up and changed the  
minimum zoom to 0.0 in GCZoomView to get around this.

At the large scale, the grid completely disappears.  The selection  
handles are now so small that you can't click on them.  Also, I pegged  
one CPU core at 100% just trying to select a couple objects at that  
zoom factor.

It looks like we might want to consider redrawing the grid on a change  
of scale, to make sure that the linewidth is always 1.0, no matter the  
scale.  I haven't looked into the selection handles (DKKnob?) yet, but  
it seems like making them aware of the scale factor would also allow  
you to redraw them with constant sizes and linewidths.  If you have  
any suggestions, I'd be glad to look into it.

Also, what would be your recommended process for automatically setting  
the scale to fit the drawing size on load of a drawing from disk?


______________________
Brad Larson
SonoPlot, Inc.
3030 Laura Lane, Suite 120
Middleton, WI 53562