[DiaCanvas] to myself, about connecting objects off-canvas

[<aur...@wa...>]

En principe, 

to connect some Line-ish object to an Element-ish object, you pick one
line's handle, drag it onto the Element's bounding box and just drop !
it's connected.

which translates to :

- a lot of calc_glue_point on the Element side (in fact, any Element
already on the canvas**),
- at drop time, the Line handle is connected to the closest glue point
of the bounding box of the Element,
- one add_line_constraint is issued (to ensure the line handle remains
glued to its landing place)

as shown on this trace (with NODE & EDGE playing for Element & Line) :
note that there are 2 nodes here, but obiously only one shall be
connected,

NODE glue
NODE calc_glue_point, dist = 166.087326
NODE glue
NODE calc_glue_point, dist = 1.414214
NODE glue
NODE calc_glue_point, dist = 166.379085
NODE glue
NODE calc_glue_point, dist = 1.000000
NODE glue
NODE calc_glue_point, dist = 166.676333
NODE glue
NODE calc_glue_point, dist = 0.000000
NODE glue
NODE calc_glue_point, dist = 165.722660

then...

NODE connect
NODE calc_glue_point, dist = 0.000000
handle add_point_constraint

The problem is : what is going on under the hood that makes things
actually work ?

When I try to programatically replicate this, typing in a pythonesque
way :


class VcEdge (dia.CanvasEdge, dia.CanvasAbstractGroup):
    def __init__(self):
        self.__gobject_init__()

    def attach (self, from_node, to_node):
        self.from_node = from_node
        self.to_node = to_node

	#two point constraints will be added :
        from_node.connect_handle (self.handles[0])  
        to_node.connect_handle (self.handles[1])

        self.request_update()
        from_node.request_update()
        to_node.request_update()


any call to attach won't really connect the edge to the nodes.
HINT : the edge is not yet on the canvas.

What's missing here ...?

Aurélien.


** this is not a good thing. It won't work with huge graphs (or
drawings). This O(n) calculus could be done just at drop-time (or
MOUSE_RELEASE time) instead of being incessantly recomputed.