How can I subtract two shapes and get resulting points of the new shape in C#?

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I have (x,y) points of two 2D shapes, which might be any type polygon but mostly rectangles. The small rectangle is inside the big one and always tangent to its circumference. I would like to subtract them (programmatically) and get resulting (x,y) points of the new polygon (but not on screen).

Can anyone give any clues on how I might accomplish this?

What I have tried:

I tried to use the System.Windows.Media.Geometry.Combine method, but to be honest I didn't understand how it works in my case.

Posted 30-Mar-19 0:55am

Mazin78

Updated 30-Mar-19 1:08am

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Patrice T 30-Mar-19 12:27pm

"I would like to subtract them"
what do you mean by subtract ?
show a sample data and expected result.

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OriginalGriff · Accepted Answer · 2019-03-30T01:09:00

Solution 1

Convert your Points to a Region (easiest way is via a GraphicsPath or a Rectangle) and you can use the various methods to get a new "shape":
Region Class (System.Drawing) | Microsoft Docs[^]
It includes useful methods like Intersect, Union, and Exclude.

Posted 30-Mar-19 1:09am

OriginalGriff

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Mazin78 31-Mar-19 8:12am

Thank you, I have used both (PathFigure and RectangleGeometry), and I got the new shape using:
CombinedGeometry(GeometryCombineMode.Exclude, myRectGeometry, myPathGeometry);
The issue now is how to get the points of the new shape? I don't want only to see the new shape on screen, but also I need the points for more processing.

OriginalGriff 31-Mar-19 8:25am

The problem is that a "shape" doesn't have "Points" - it's an "area" instead - so the bare points (which are what you used to generate the shape) don't define it in any meaningful way, because bare points don't indicate "hollowness" which is the shape your description implies.

What - exactly - are you trying to use this for?

Mazin78 31-Mar-19 8:34am

I need the points of the new shape for two reasons:
1- Exporting them to an application that draw 3D shapes based on 2D points.
2- I can use the new shape as an original one, then exclude another shape from it.