The same, with an undo checkpoint taken first. Which of the two to use is decided by whether the operation has already pushed one: an edit that took a checkpoint before changing anything wants that ONE entry to cover the whole thing, re-routing included, so that Ctrl-Z puts back what the user was looking at rather than an intermediate state they never saw. Use this one where the operation takes no checkpoint of its own - the menu redraws, and anything that only re-routes.

Whether a mouse-down at this point leaves a symbol edit mode running. Clicking the symbol itself, or one of its ports or corners, is part of using the mode; anything else is the user moving on, which is what ends it.

Fit the circuit to `winOpt`, which is the drawing area less anything covering it - see Sheet.fitWindowFor, which works it out from the whole Issie model. None when there is no canvas to measure, and so nothing to fit to.

Geometric helper used for testing. Probably needs a better name, and to be collected with other This should perhaps be generalised for all orientations and made a helper function. However different testing may be needed, so who knows? Return the vertical channel between two bounding boxes, if they do not intersect and their vertical coordinates overlap.

Mouse Down Update, Can have clicked on: Label, InputPort / OutputPort / Component / Wire / Canvas. Do correct action for each.

Mouse Drag Update, can be: drag-to-selecting, moving symbols, connecting wire between ports.

Mouse Move Update, looks for nearby components and looks if mouse is on a port

Mouse Up Update, can have: finished drag-to-select, pressed on a component, finished symbol movement, connected a wire between ports

Update function to move symbols in model.SelectedComponents

True when this port belongs to the symbol whose ports the user has asked to move. Ports of every other symbol keep their normal behaviour of starting a wire.

Route every floating wire again from nothing and separate the whole sheet. **What a UI operation ends with**, once it has finished changing the sheet - not while it is changing it. A delete removes several things, a rotate turns a whole selection, a drag moves a symbol through a hundred positions: each is one change as far as the drawing is concerned, and re-routing part of the way through would lay wires out for a sheet that is about to be different. So this goes at the END, once, and a drag calls it on mouse-UP. Hand-routed wires are not re-routed - see redrawFloatingWires - but the whole sheet, including them, is separated.

Inputs are segment ID being dragged and new mouse position. Performs the Segment Drag operation implementing snaps. This function must be in update and creates additional commands to implement the drag oeporation.