[Drawkit] Handling drawing primitives

[Brad Larson]

I'm running into a little difficulty in our drawing application  
regarding primitives, such as arcs, rectangles, and circles.  When  
loading from our simple XML file format, which specifies simple  
shapes, I have no problem creating objects, either by helper functions  
like initWithRect or by creating an NSBezierPath representative of the  
primitive.  Where I'm having problems are the editing and file saving  
operations.

For file saving, the only way I can see to access the geometry of the  
DKDrawableShapes and DKDrawablePaths is through their NSBezierPaths.   
This adds a little challenge, because a rectangle is no longer just a  
rectangle with a length and width, it is now a five-element  
NSBezierPath (an initial NSMoveToBezierPathElement, four  
NSLineToBezierPathElements, and an NSClosePathBezierPathElement).  You  
now have to intelligently parse out this structure and recognize that  
it is a rectangle, calculate the length and width, and write it out to  
a file.  Circles and arcs are even worse, because there are a variable  
number of curve points and you have to calculate the center point and  
radius from the lines defined by the control points.  I'm working on  
this right now, and I think it's doable, it's just taking a bit of  
thought.

The part that's really causing me problems is editing these  
primitives.  The arc drawing tool is really slick, but when it's done  
it leaves behind a bezier path.  It would make more sense to be able  
to edit the arc by dragging the ends for the starting and ending  
angles, as well as the center point.  You could still convert this arc  
to a path if you really wanted a bezier path to work with.  Our  
machine does not handle bezier paths right now, and the most it can  
deal with are arcs, so I'd like to keep editing an arc as an arc.   
Another example is a rounded rectangle.  Once it is drawn, I don't see  
a means for changing the rounding radius short of dealing with it as a  
path.

Could this be handled through subclassing DKDrawableShape?  For  
example, a DKDrawableArc that has a center point, starting and ending  
angles (or points), and maybe a clockwise / counterclockwise boolean  
value could be edited as a shape with specific control points.  The  
arc DKDrawingTool would create one, and it would simplify the loading  
and saving process for this primitive.  Similar subclasses could be  
created for other primitives.  However, I might be missing something  
about the architecture of the framework that would make this  
unnecessary.

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