如何在python-pptx中获取给定形状的连接点坐标

Question

My task is to connect an arrow/line from shape1 to shape2. While doing so, I need to get the exact co-ordinates of connecting points along the perimeter of shape. To be clear, by connecting points I mean the small green bubbles you see along the perimeter of a shape when you try to connect an arrow/line to it in the powerpoint tool. I am interested only in these points as the PPT software adds visually appealing alignments if connected to those points.

In existing code, there are two functions _move_begin_to_cxn() and _move_end_to_cxn() , which share common logic, where they get the connecting points' coordinates. But this works only in case of a rectangle. This is since we only have top-left location and width-height of the shape.

    def _move_end_to_cxn(self, shape, cxn_pt_idx):
        """
        Move the end point of this connector to the coordinates of the
        connection point of *shape* specified by *cxn_pt_idx*.
        """
        x, y, cx, cy = shape.left, shape.top, shape.width, shape.height
        self.end_x, self.end_y = {
            0: (int(x + cx / 2), y),
            1: (x, int(y + cy / 2)),
            2: (int(x + cx / 2), y + cy),
            3: (x + cx, int(y + cy / 2)),
        }[cxn_pt_idx]

This is difficult to compute for complicated shapes - such as oval, pentagon, parallelogram - with just the top-left location and width-height.

Is there any efficient way to get the accurate location of the connectable points? Any help would be appreciated.

Thanks in advance!

Answer 1

There is no smooth equation to get those points for an arbitrary shape. PPT hard-codes those points, parameterized to the bounding box, and simply activates them when appropriate.

Fortunately, you don't have to compute them to thirteen significant figures. One simple-but-tedious way to get the points is to hard-code them yourself. Create a desired shape in PPT, enlarge it as far as you can, and read the relative coordinates from that enlargement. Store those parameters in a list with each shape.

Another straightforward way is to examine the connection points for each shape; they're all extreme points and midpoints of edges or arcs. Use basic analytic geometry to compute the relative coordinates of each point. Again, hard-code these into your application.

Whichever way you pick, you might be off by a pixel or two, but that will be close enough for PPT to recognize that you want the connection.