[Bf-blender-cvs] [b30d103cf63] blender2.8: Cloth: Fix mistake in big matrix multiplication

[Luca Rood]

Commit: b30d103cf63ced54473b49b4160faf3e53a9a530
Author: Luca Rood
Date:   Fri Aug 17 13:08:47 2018 +0200
Branches: blender2.8
https://developer.blender.org/rBb30d103cf63ced54473b49b4160faf3e53a9a530

Cloth: Fix mistake in big matrix multiplication

Only the upper triangle of the block matrix is stored, thus when
executing operations on the lower triangle, each block must be
transposed. This transposition was not ocurring in the matrix-vector
multiplication function, which is fixed by this commit.

Reviewed By: brecht

Differential Revision: http://developer.blender.org/D3619

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

M	source/blender/physics/intern/implicit_blender.c

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

diff --git a/source/blender/physics/intern/implicit_blender.c b/source/blender/physics/intern/implicit_blender.c
index 5fd9c6b50de..ddd71eb93e3 100644
--- a/source/blender/physics/intern/implicit_blender.c
+++ b/source/blender/physics/intern/implicit_blender.c
@@ -456,6 +456,13 @@ DO_INLINE void muladd_fmatrix_fvector(float to[3], float matrix[3][3], float fro
 	to[2] += dot_v3v3(matrix[2], from);
 }
 
+DO_INLINE void muladd_fmatrixT_fvector(float to[3], float matrix[3][3], float from[3])
+{
+	to[0] += matrix[0][0] * from[0] + matrix[1][0] * from[1] + matrix[2][0] * from[2];
+	to[1] += matrix[0][1] * from[0] + matrix[1][1] * from[1] + matrix[2][1] * from[2];
+	to[2] += matrix[0][2] * from[0] + matrix[1][2] * from[1] + matrix[2][2] * from[2];
+}
+
 BLI_INLINE void outerproduct(float r[3][3], const float a[3], const float b[3])
 {
 	mul_v3_v3fl(r[0], a, b[0]);
@@ -599,7 +606,9 @@ DO_INLINE void mul_bfmatrix_lfvector( float (*to)[3], fmatrix3x3 *from, lfVector
 #pragma omp section
 		{
 			for (i = from[0].vcount; i < from[0].vcount+from[0].scount; i++) {
-				muladd_fmatrix_fvector(to[from[i].c], from[i].m, fLongVector[from[i].r]);
+				/* This is the lower triangle of the sparse matrix,
+				 * therefore multiplication occurs with transposed submatrices. */
+				muladd_fmatrixT_fvector(to[from[i].c], from[i].m, fLongVector[from[i].r]);
 			}
 		}
 #pragma omp section
@@ -612,8 +621,6 @@ DO_INLINE void mul_bfmatrix_lfvector( float (*to)[3], fmatrix3x3 *from, lfVector
 	add_lfvector_lfvector(to, to, temp, from[0].vcount);
 
 	del_lfvector(temp);
-
-
 }
 
 /* SPARSE SYMMETRIC sub big matrix with big matrix*/