Knife tool: simplify hit-depth calculation

source/blender/blenlib/intern/math_vector_inline.c

@@ -466,7 +466,7 @@ MINLINE float mul_project_m4_v3_zfac(float mat[4][4], const float co[3])
 }
 
 /**
- * Has the effect of mul_m3_v3(), on a single axis.
+ * Has the effect of #mul_m3_v3(), on a single axis.
  */
 MINLINE float dot_m3_v3_row_x(float M[3][3], const float a[3])
 {
@@ -482,7 +482,8 @@ MINLINE float dot_m3_v3_row_z(float M[3][3], const float a[3])
 }
 
 /**
- * Almost like mul_m4_v3(), misses adding translation.
+ * Has the effect of #mul_mat3_m4_v3(), on a single axis.
+ * (no adding translation)
  */
 MINLINE float dot_m4_v3_row_x(float M[4][4], const float a[3])
 {