Understanding hatches algorithm

NikhilPundir — Wed, 13 Mar 2024 20:23:47 GMT

I am implementing a dxf viewer for hatches and to do that I am trying to understand the algorithm used by AutoCAD for island and boundary detection. I am able to load the data correctly from dxf code.

My research showed me that Autocad uses ray casting, island detection and flood fill method to create hatch boundaries.

There are 3 different type of hatches

1. Simple hatches which only contain single close boundary. These are simple to implement but becomes complex if the boundary self intersect

2. Hatches formed by intersection of multiple entities and use a seed point & flood fill method to find the close boundary.

3. Open hatches created by selecting entities instead of seed point. I am guessing AutoCad uses flood fill for this too.

Is this info correct? Can someone provide more information and specific algorithm names that is used by AutoCad ?

It will be really helpful for me. Thanks!!

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Understanding hatches algorithm