Fix T77261: Multires creates spikes when subdividing ngons

The spikes were caused by non-initialized tangent matrix used during
smoothing process. The reason tangent matrix was not initialized was
because wrong usage of API: n-gons should pass corner of 0 to the
matrix construction function.

Corrected usage of the API and added assert() to help catching such
kind of non-initialized issues easier.

1 files changed, 4 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/multires_inline.h b/source/blender/blenkernel/intern/multires_inline.h
index 49329698b3a..e85aa12781e 100644
--- a/source/blender/blenkernel/intern/multires_inline.h
+++ b/source/blender/blenkernel/intern/multires_inline.h
@@ -25,6 +25,7 @@
 
 #include "BKE_multires.h"
 #include "BLI_math_vector.h"
+#include "BLI_utildefines.h"
 
 BLI_INLINE void BKE_multires_construct_tangent_matrix(float tangent_matrix[3][3],
                                                       const float dPdu[3],
@@ -51,6 +52,9 @@ BLI_INLINE void BKE_multires_construct_tangent_matrix(float tangent_matrix[3][3]
     copy_v3_v3(tangent_matrix[1], dPdv);
     mul_v3_fl(tangent_matrix[0], -1.0f);
   }
+  else {
+    BLI_assert(!"Unhandled corner index");
+  }
   cross_v3_v3v3(tangent_matrix[2], dPdu, dPdv);
   normalize_v3(tangent_matrix[0]);
   normalize_v3(tangent_matrix[1]);