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-rw-r--r--libdimension/geometry.c60
1 files changed, 32 insertions, 28 deletions
diff --git a/libdimension/geometry.c b/libdimension/geometry.c
index e9c2122..edb73cd 100644
--- a/libdimension/geometry.c
+++ b/libdimension/geometry.c
@@ -80,35 +80,39 @@ dmnsn_rotation_matrix(dmnsn_vector theta)
dmnsn_vector axis, n1, n2, n3;
double angle, s, t, x, y, z;
- axis = dmnsn_vector_normalize(theta);
angle = dmnsn_vector_norm(theta);
-
- /* Shorthand to fit logical lines on one line */
-
- s = sin(angle);
- t = 1.0 - cos(angle);
-
- x = axis.x;
- y = axis.y;
- z = axis.z;
-
- /* Construct vectors, then a matrix, so our dmnsn_matrix_construct() call
- is reasonably small */
-
- n1 = dmnsn_vector_construct(1.0 + t*(x*x - 1.0),
- z*s + t*x*y,
- -y*s + t*x*z);
- n2 = dmnsn_vector_construct(-z*s + t*x*y,
- 1.0 + t*(y*y - 1.0),
- x*s + t*y*z);
- n3 = dmnsn_vector_construct(y*s + t*x*z,
- -x*s + t*y*z,
- 1.0 + t*(z*z - 1.0));
-
- return dmnsn_matrix_construct(n1.x, n2.x, n3.x, 0.0,
- n1.y, n2.y, n3.y, 0.0,
- n1.z, n2.z, n3.z, 0.0,
- 0.0, 0.0, 0.0, 1.0);
+ if (angle != 0.0) {
+ axis = dmnsn_vector_normalize(theta);
+
+ /* Shorthand to fit logical lines on one line */
+
+ s = sin(angle);
+ t = 1.0 - cos(angle);
+
+ x = axis.x;
+ y = axis.y;
+ z = axis.z;
+
+ /* Construct vectors, then a matrix, so our dmnsn_matrix_construct() call
+ is reasonably small */
+
+ n1 = dmnsn_vector_construct(1.0 + t*(x*x - 1.0),
+ z*s + t*x*y,
+ -y*s + t*x*z);
+ n2 = dmnsn_vector_construct(-z*s + t*x*y,
+ 1.0 + t*(y*y - 1.0),
+ x*s + t*y*z);
+ n3 = dmnsn_vector_construct(y*s + t*x*z,
+ -x*s + t*y*z,
+ 1.0 + t*(z*z - 1.0));
+
+ return dmnsn_matrix_construct(n1.x, n2.x, n3.x, 0.0,
+ n1.y, n2.y, n3.y, 0.0,
+ n1.z, n2.z, n3.z, 0.0,
+ 0.0, 0.0, 0.0, 1.0);
+ } else {
+ return dmnsn_identity_matrix();
+ }
}
/* Add two vectors */