New math function to add small bias to zero axis

In some situations the zero axis can produce problems and need to add a small bias.

This function adds a small bias using the orthogonal result of the others valid axis.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D16158
6d

2 files changed, 30 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_math_matrix.h b/source/blender/blenlib/BLI_math_matrix.h
index 19943614881..7e1b7c2ba56 100644
--- a/source/blender/blenlib/BLI_math_matrix.h
+++ b/source/blender/blenlib/BLI_math_matrix.h
@@ -367,6 +367,8 @@ void pseudoinverse_m4_m4(float inverse[4][4], const float mat[4][4], float epsil
 void pseudoinverse_m3_m3(float inverse[3][3], const float mat[3][3], float epsilon);
 
 bool has_zero_axis_m4(const float matrix[4][4]);
+/** Fix any zero scale axis adding a small bias orthogonal to the other valid axis. */
+void zero_axis_bias_m4(float mat[4][4]);
 
 void invert_m4_m4_safe(float inverse[4][4], const float mat[4][4]);
 
diff --git a/source/blender/blenlib/intern/math_matrix.c b/source/blender/blenlib/intern/math_matrix.c
index 221ae84e74d..d997eae26fb 100644
--- a/source/blender/blenlib/intern/math_matrix.c
+++ b/source/blender/blenlib/intern/math_matrix.c
@@ -3116,6 +3116,34 @@ bool has_zero_axis_m4(const float matrix[4][4])
          len_squared_v3(matrix[2]) < FLT_EPSILON;
 }
 
+void zero_axis_bias_m4(float mat[4][4])
+{
+  const bool axis_x_degenerate = len_squared_v3(mat[0]) < FLT_EPSILON;
+  const bool axis_y_degenerate = len_squared_v3(mat[1]) < FLT_EPSILON;
+  const bool axis_z_degenerate = len_squared_v3(mat[2]) < FLT_EPSILON;
+
+  /* X Axis. */
+  if (axis_x_degenerate && !axis_y_degenerate && !axis_z_degenerate) {
+    cross_v3_v3v3(mat[0], mat[1], mat[2]);
+    mul_v3_fl(mat[0], FLT_EPSILON);
+    return;
+  }
+
+  /* Y Axis. */
+  if (!axis_x_degenerate && axis_y_degenerate && !axis_z_degenerate) {
+    cross_v3_v3v3(mat[1], mat[2], mat[0]);
+    mul_v3_fl(mat[1], FLT_EPSILON);
+    return;
+  }
+
+  /* Z Axis. */
+  if (!axis_x_degenerate && !axis_y_degenerate && axis_z_degenerate) {
+    cross_v3_v3v3(mat[2], mat[0], mat[1]);
+    mul_v3_fl(mat[2], FLT_EPSILON);
+    return;
+  }
+}
+
 void invert_m4_m4_safe(float inverse[4][4], const float mat[4][4])
 {
   if (!invert_m4_m4(inverse, mat)) {