Cycles: Fix issues with quick inverse of degenerate matrix

This fixes part of the issues reported in T46322. Still need to solve
issue with wrong intersection distance scaling.

1 files changed, 6 insertions, 1 deletions

diff --git a/intern/cycles/util/util_transform.h b/intern/cycles/util/util_transform.h
index ba8d04b5c16..44502737ec6 100644
--- a/intern/cycles/util/util_transform.h
+++ b/intern/cycles/util/util_transform.h
@@ -347,7 +347,12 @@ ccl_device_inline Transform transform_quick_inverse(Transform M)
 	 * scale can be inverted but what about shearing? */
 	Transform R;
 	float det = M.x.x*(M.z.z*M.y.y - M.z.y*M.y.z) - M.y.x*(M.z.z*M.x.y - M.z.y*M.x.z) + M.z.x*(M.y.z*M.x.y - M.y.y*M.x.z);
-
+	if(det == 0.0f) {
+		M[0][0] += 1e-8f;
+		M[1][1] += 1e-8f;
+		M[2][2] += 1e-8f;
+		det = M.x.x*(M.z.z*M.y.y - M.z.y*M.y.z) - M.y.x*(M.z.z*M.x.y - M.z.y*M.x.z) + M.z.x*(M.y.z*M.x.y - M.y.y*M.x.z);
+	}
 	det = (det != 0.0f)? 1.0f/det: 0.0f;
 
 	float3 Rx = det*make_float3(M.z.z*M.y.y - M.z.y*M.y.z, M.z.y*M.x.z - M.z.z*M.x.y, M.y.z*M.x.y - M.y.y*M.x.z);