Handles appear around the perimeter of a selected element as small squares in the selection color. If the cursor is moved over one of these handles, it changes to indicate its proximity to the handle. When clicking on a handle, the user can then resize or reshape the element based on the handle's reshaping rules.
Component footprints can also have handles which can be specified in the footprint editor. These handles can likewise be used to reshape a component footprint, and at the same time altering one or more of its electrical parameters. In other words, the user can use handles to directly manipulate an element's geometry corresponding to electrical parameters.
Defining a Handle
Open the footprint editor for the footprint appropriate. From the Draw menu, choose Handle. Next, click to place the handle anywhere in the drawing, exact placement does not matter.
Editing Handle Location
Next, open the property window (Edit > Properties). There is one property listed: location. For this property, edit the X & Y locations to place the handle in the correct position based on the parameters.
Specifying Parameters to Change
Next, click Add in the Property window. In the responding window, specify the name of the electrical parameter, and the expression, based on the X & Y location of the handle that sets this parameter. For example:
Edit the footprint for the MSTRL component. Place a handle that is on the top edge of the line. The component has the parameters P for length and W for width. The handle has its location (X,Y) set to: (P/2, W/2). One property is added called "W" and its expression is "abs(Y*2)". The "abs" (absolute value) of "Y*2" ensures that as Y approaches zero, the line width stays positive. The two entries in the window should look like the following:
Location: P/2, W/2
W: abs(Y*2)
How it works
When the user drags the handle, for each new location of the cursor, each of the handles properties are recalculated for that new position. For the TRL example, the y position of the top-side handle is used to set the line's "w", which of course is twice that of y. After the new parameter values are calculated, the handle's own position is recalculated based on the updated parameters and the expressions for its location. Thus, as the cursor goes up, the line gets wider, and the handle tracks with the new width.