Cutting holes in PathGeometry

Question

I have a PathGeometry defining some path like this:

source path http://devblog.ailon.org/devblog/_stuff/wpfpathgeoquestion/original.gif

This is a simplified example. In fact, it can have segments of any type (Line, Arc, Bezier).

Now I need to cut out a hole of some kind and size (square, circle, etc.) in the nodes of the segment, so the final result looks something like this:

with holes http://devblog.ailon.org/devblog/_stuff/wpfpathgeoquestion/with_holes.gif

My initial idea was to combine the original PathGeometry with other geometries containing squares (or something else) at the joint points using GeometryCombineMode.Exclude. Unfortunately, this creates empty geometry if the path is not filled. And if it is full, it produces the wrong result.

So I'm stuck. In a simple example with line segments, I could calculate the boundary points in advance and make my line segments complete there, but with arcs and beziers it would be a sort of sorting.

Does anyone have an idea how to do this?

Note. I need these holes to be erased (transparent), so placing a white square above it will not work.

Answer 1

A. Did it. The idea is to create an OpacityMask from your holes using a DrawingBrush, and then click on the drawing context before drawing the PathGeometry. Something like that.

RectangleGeometry r = new RectangleGeometry(graphVisual.Bounds); GeometryDrawing dr = new GeometryDrawing(Brushes.Black, null, Geometry.Combine(r, bulletHoles, GeometryCombineMode.Exclude, null)); DrawingBrush br = new DrawingBrush(dr); drawingContext.PushOpacityMask(br); drawingContext.DrawGeometry(null, new Pen(Brushes.Green, 2), graphVisual); drawingContext.Pop();