Cycles: Fix for watertight intersection

It was possible to miss some intersection caused by wrong barycentric
coordinates sign.

Cases when one of the coordinate is zero and other are negative was not
handled correct.

1 files changed, 5 insertions, 8 deletions

diff --git a/intern/cycles/kernel/geom/geom_triangle_intersect.h b/intern/cycles/kernel/geom/geom_triangle_intersect.h
index ba309a1dc53..1ce4eea48f4 100644
--- a/intern/cycles/kernel/geom/geom_triangle_intersect.h
+++ b/intern/cycles/kernel/geom/geom_triangle_intersect.h
@@ -142,12 +142,8 @@ ccl_device_inline bool triangle_intersect(KernelGlobals *kg,
 	float U = Cx * By - Cy * Bx;
 	float V = Ax * Cy - Ay * Cx;
 	float W = Bx * Ay - By * Ax;
-	const int sign_mask = (__float_as_int(U) & 0x80000000);
-	/* TODO(sergey): Check if multiplication plus sign check is faster
-	 * or at least same speed (but robust for endian types).
-	 */
-	if(sign_mask != (__float_as_int(V) & 0x80000000) ||
-	   sign_mask != (__float_as_int(W) & 0x80000000))
+	if ((U < 0.0f || V < 0.0f || W < 0.0f) &&
+	    (U > 0.0f || V > 0.0f || W > 0.0f))
 	{
 		return false;
 	}
@@ -162,9 +158,10 @@ ccl_device_inline bool triangle_intersect(KernelGlobals *kg,
 	 * the hit distance.
 	 */
 	const float T = (U * A_kz + V * B_kz + W * C_kz) * Sz;
-	const float sign_T = xor_signmask(T, sign_mask);
+	const int sign_det = (__float_as_int(det) & 0x80000000);
+	const float sign_T = xor_signmask(T, sign_det);
 	if((sign_T < 0.0f) ||
-	   (sign_T > isect->t * xor_signmask(det, sign_mask)))
+	   (sign_T > isect->t * xor_signmask(det, sign_det)))
 	{
 		return false;
 	}