some wrong edges selected after knife project #45009

New Issue

mathieu menuet · 2015-06-09T21:52:30+02:00

mathieu menuet commented

2015-06-09 21:52:30 +02:00

System Information
Win7 x64

Blender Version
Broken: 94e7ac5

Short description of error
After calling "knife project" some edges are in the selection although they shouldn't.

Exact steps for others to reproduce the error
Open Attached file, call "knife project"
bug_knife_project_selection.blend
You get this:

Notice the triangle in red circle which shouldn't be selected.

**System Information** Win7 x64 **Blender Version** Broken: 94e7ac5 **Short description of error** After calling "knife project" some edges are in the selection although they shouldn't. **Exact steps for others to reproduce the error** Open Attached file, call "knife project" [bug_knife_project_selection.blend](https://archive.blender.org/developer/F188429/bug_knife_project_selection.blend) You get this: ![bug knife project selection.png](https://archive.blender.org/developer/F188430/bug_knife_project_selection.png) Notice the triangle in red circle which shouldn't be selected.

mathieu menuet commented

2015-06-09 21:52:30 +02:00

Changed status to: 'Open'

mathieu menuet commented

2015-06-09 21:52:30 +02:00

Added subscriber: @bliblubli

Bastien Montagne commented

2015-06-10 13:29:22 +02:00

Added subscribers: @ideasman42, @mont29

Bastien Montagne self-assigned this 2015-06-10 13:29:22 +02:00

Bastien Montagne commented

2015-06-10 13:29:22 +02:00

Hehe, was fun to track down… So, issue comes from erroneous code to chose a point inside a 'knife face' (edbm_mesh_knife_face_point()) - computing the area of triangulated face is rather fantasist, this oneliner patch fixes it:

P232: #45009

diff --git a/source/blender/editors/mesh/editmesh_knife.c b/source/blender/editors/mesh/editmesh_knife.c
index cfd0d3f..b7e1128 100644
--- a/source/blender/editors/mesh/editmesh_knife.c
+++ b/source/blender/editors/mesh/editmesh_knife.c
@@ -3371,9 +3371,7 @@ static void edbm_mesh_knife_face_point(BMFace *f, float r_cent[3])
 		const float *p3 = loops[index- [x]- [x]]->v->co;
 		float area;
 
-		float cross[3];
-		cross_v3_v3v3(cross, p2, p3);
-		area = fabsf(dot_v3v3(p1, cross));
+		area = area_squared_tri_v3(p1, p2, p3);
 		if (area > area_best) {
 			j_best = j;
 			area_best = area;

Note that the issue only appears when triangulation of the face produces degenerated triangles, with all three points aligned on a cutting edge, which is the case in this example. Quite a nice corner case. ;)

@ideasman42 see anything wrong in proposed patch?

Hehe, was fun to track down… So, issue comes from erroneous code to chose a point inside a 'knife face' (`edbm_mesh_knife_face_point()`) - computing the area of triangulated face is rather fantasist, this oneliner patch fixes it: [P232: #45009](https://archive.blender.org/developer/P232.txt) ``` diff --git a/source/blender/editors/mesh/editmesh_knife.c b/source/blender/editors/mesh/editmesh_knife.c index cfd0d3f..b7e1128 100644 --- a/source/blender/editors/mesh/editmesh_knife.c +++ b/source/blender/editors/mesh/editmesh_knife.c @@ -3371,9 +3371,7 @@ static void edbm_mesh_knife_face_point(BMFace *f, float r_cent[3]) const float *p3 = loops[index- [x]- [x]]->v->co; float area; - float cross[3]; - cross_v3_v3v3(cross, p2, p3); - area = fabsf(dot_v3v3(p1, cross)); + area = area_squared_tri_v3(p1, p2, p3); if (area > area_best) { j_best = j; area_best = area; ``` Note that the issue only appears when triangulation of the face produces degenerated triangles, with all three points aligned on a cutting edge, which is the case in this example. Quite a nice corner case. ;) @ideasman42 see anything wrong in proposed patch?

Bastien Montagne commented

2015-06-10 13:30:44 +02:00

Btw, this code can still theoretically generate points outside of actual quad face...