Although removing the dragComputation lets me move there, but even lets me overlap groups, which I do not want. Below is my implementation for dragComputation. Is it possible to not allow it to overlap polygonal group into its actual boundary by calculating non-rectangular boundaries ?
function isUnoccupied(r, node) {
var diagram = node.diagram;
// nested function used by Layer.findObjectsIn, below
// only consider Parts, and ignore the given Node and any Links
function navig(obj) {
var part = obj.part;
if (part === node) return null;
if (part instanceof go.Link) return null;
// add these two checks:
if (part.isMemberOf(node)) return null;
if (node.isMemberOf(part)) return null;
return part;
}
// only consider non-temporary Layers
var lit = diagram.layers;
while (lit.next()) {
var lay = lit.value;
if (lay.isTemporary) continue;
if (lay.findObjectsIn(r, navig, null, true).count > 0) return false;
}
return true;
}
// a Part.dragComputation function that prevents a Part from being dragged to overlap another Part
function avoidNodeOverlap(node, pt, gridpt) {
if (node.diagram instanceof go.Palette) return gridpt;
// this assumes each node is fully rectangular
var bnds = node.actualBounds;
var loc = node.location;
// use PT instead of GRIDPT if you want to ignore any grid snapping behavior
// see if the area at the proposed location is unoccupied
var r = new go.Rect(
gridpt.x - (loc.x - bnds.x),
gridpt.y - (loc.y - bnds.y),
bnds.width,
bnds.height
);
// maybe inflate R if you want some space between the node and any other nodes
r.inflate(-0.5, -0.5); // by default, deflate to avoid edge overlaps with "exact" fits
// when dragging a node from another Diagram, choose an unoccupied area
if (
!(node.diagram.currentTool instanceof go.DraggingTool) &&
(!node._temp || !node.layer.isTemporary)
) {
// in Temporary Layer during external drag-and-drop
node._temp = true; // flag to avoid repeated searches during external drag-and-drop
while (!isUnoccupied(r, node)) {
r.x += 10; // note that this is an unimaginative search algorithm --
r.y += 10; // you can improve the search here to be more appropriate for your app
}
r.inflate(0.5, 0.5); // restore to actual size
// return the proposed new location point
return new go.Point(r.x - (loc.x - bnds.x), r.y - (loc.y - bnds.y));
}
if (isUnoccupied(r, node)) return gridpt; // OK
return loc; // give up -- don't allow the node to be moved to the new location
}