[Bf-blender-cvs] [40ef25d] master: Fix T43891: Skin modifier inverts some faces

[Campbell Barton]

Commit: 40ef25d000b3708ee1fb408077ac591ed59158d6
Author: Campbell Barton
Date:   Mon Mar 9 20:23:32 2015 +1100
Branches: master
https://developer.blender.org/rB40ef25d000b3708ee1fb408077ac591ed59158d6

Fix T43891: Skin modifier inverts some faces

===================================================================

M       source/blender/modifiers/intern/MOD_skin.c

===================================================================

diff --git a/source/blender/modifiers/intern/MOD_skin.c 
b/source/blender/modifiers/intern/MOD_skin.c
index 2bde963..4a99168 100644
--- a/source/blender/modifiers/intern/MOD_skin.c
+++ b/source/blender/modifiers/intern/MOD_skin.c
@@ -965,23 +965,51 @@ static void add_poly(SkinOutput *so,
        f->mat_nr = so->mat_nr;
 }
 
-static void connect_frames(SkinOutput *so,
-                           BMVert *frame1[4],
-BMVert *frame2[4])
+static void connect_frames(
+        SkinOutput *so,
+        BMVert *frame1[4],
+        BMVert *frame2[4])
 {
        BMVert *q[4][4] = {{frame2[0], frame2[1], frame1[1], frame1[0]},
                           {frame2[1], frame2[2], frame1[2], frame1[1]},
                           {frame2[2], frame2[3], frame1[3], frame1[2]},
                           {frame2[3], frame2[0], frame1[0], frame1[3]}};
-       float p[3], no[3];
-       int i, swap;
+       int i;
+       bool swap;
 
        /* Check if frame normals need swap */
-       sub_v3_v3v3(p, q[3][0]->co, q[0][0]->co);
-       normal_quad_v3(no,
-                      q[0][0]->co, q[0][1]->co,
-                      q[0][2]->co, q[0][3]->co);
-       swap = dot_v3v3(no, p) > 0;
+#if 0
+       {
+               /* simple method, works mostly */
+               float p[3], no[3];
+               sub_v3_v3v3(p, q[3][0]->co, q[0][0]->co);
+               normal_quad_v3(no,
+                       q[0][0]->co, q[0][1]->co,
+                       q[0][2]->co, q[0][3]->co);
+               swap = dot_v3v3(no, p) > 0;
+       }
+#else
+       {
+               /* comprehensive method, accumulate flipping of all faces */
+               float cent_sides[4][3];
+               float cent[3];
+               float dot = 0.0f;
+
+               for (i = 0; i < 4; i++) {
+                       mid_v3_v3v3v3v3(cent_sides[i], UNPACK4_EX(,q[i],->co));
+               }
+               mid_v3_v3v3v3v3(cent, UNPACK4(cent_sides));
+
+               for (i = 0; i < 4; i++) {
+                       float p[3], no[3];
+                       normal_quad_v3(no, UNPACK4_EX(,q[i],->co));
+                       sub_v3_v3v3(p, cent, cent_sides[i]);
+                       dot += dot_v3v3(no, p);
+               }
+
+               swap = dot > 0;
+       }
+#endif
 
        for (i = 0; i < 4; i++) {
                if (swap)

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