Problem creating a concave polygon #35187

New Issue

Ondrej Vencovsky · 2013-05-02T11:23:50+02:00

Ondrej Vencovsky commented

2013-05-02 11:23:50 +02:00

%%%--- Operating System, Graphics card ---
OS: Windows 7 Ultimate (x64) - Czech Regional Settings
GC: Not important, the same happens on different configurations (Nvidia GTX570 | ATI HD 3000)

- Blender version with error, and version that worked ---

Blender 2.66 & Blender 2.67RC - both causes the same behavior.

- Short description of error ---

I have a problem creating the "concave" four-sided polygon in Blender.

The best is to see the picture.
I want to fill the arrow-shaped, 4 vertex hole with a polygon so I select all those 4 vertices and hit "F"
What Blender creates you can see in the right part of the picture - a triangle. Like if it ignored that "inside" vertex.
The same thing happens when I try to create the polygon of this shape using "knife" tool.
However, when I create two 3-point polygons first and then dissolve the middle edge, Blender holds the polygon well.

- Steps for others to reproduce the error (preferably based on attached .blend file) ---

Select all four vertices in the hole and hit "F".
%%%

%%%--- Operating System, Graphics card --- OS: Windows 7 Ultimate (x64) - Czech Regional Settings GC: Not important, the same happens on different configurations (Nvidia GTX570 | ATI HD 3000) - Blender version with error, and version that worked --- Blender 2.66 & Blender 2.67RC - both causes the same behavior. - Short description of error --- I have a problem creating the "concave" four-sided polygon in Blender. The best is to see the picture. I want to fill the arrow-shaped, 4 vertex hole with a polygon so I select all those 4 vertices and hit "F" What Blender creates you can see in the right part of the picture - a triangle. Like if it ignored that "inside" vertex. The same thing happens when I try to create the polygon of this shape using "knife" tool. However, when I create two 3-point polygons first and then dissolve the middle edge, Blender holds the polygon well. - Steps for others to reproduce the error (preferably based on attached .blend file) --- Select all four vertices in the hole and hit "F". %%%

Ondrej Vencovsky commented

2013-05-02 11:23:50 +02:00

Changed status to: 'Open'

Sergey Sharybin commented

2013-05-02 12:03:08 +02:00

%%%In this particular case face is not just concave, but it's non-flat as well. It's just mathematically not defined what's the right behavior here. You need to use smaller concave/flat faces instead.

It is probably fair to expect concave flat faces to always be tesselated fine, but this also a tricky thing -- for example if your mesh is animated, preserving nice concave faces will lead to flickering.

Leaving to Campbell for final decision here.%%%

%%%In this particular case face is not just concave, but it's non-flat as well. It's just mathematically not defined what's the right behavior here. You need to use smaller concave/flat faces instead. It is probably fair to expect concave flat faces to always be tesselated fine, but this also a tricky thing -- for example if your mesh is animated, preserving nice concave faces will lead to flickering. Leaving to Campbell for final decision here.%%%

Ondrej Vencovsky commented

2013-05-02 13:34:43 +02:00

%%%Well, you're right it's not planar. But the same happens with planar polygons.
I tried to quickly create the blender file for you and I accidentaly rotated the center polygon in perspective view instead of in orthographics view. I'm sorry.
But I'm sure it happens in 100% planar polygons too.
%%%

%%%Well, you're right it's not planar. But the same happens with planar polygons. I tried to quickly create the blender file for you and I accidentaly rotated the center polygon in perspective view instead of in orthographics view. I'm sorry. But I'm sure it happens in 100% planar polygons too. %%%

Campbell Barton commented

2013-05-02 22:37:35 +02:00

%%%This is a know limitation in blender at the moment,
Added TODO.

http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Tools#Mesh_Editing

Concave quads are currently not supported (but convex ngons are).

%%%

%%%This is a know limitation in blender at the moment, Added TODO. http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/Tools#Mesh_Editing - Concave quads are currently not supported (but convex ngons are). %%%

Campbell Barton commented

2013-05-02 22:37:35 +02:00

Changed status from 'Open' to: 'Archived'

Campbell Barton closed this issue

2013-05-02 22:37:35 +02:00

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Problem creating a concave polygon #35187