Cycles: some tiny hair intersection optimizations that help maybe 2%.

1 files changed, 41 insertions, 32 deletions

diff --git a/intern/cycles/kernel/geom/geom_curve.h b/intern/cycles/kernel/geom/geom_curve.h
index 57fa0388842..32f6a88dce2 100644
--- a/intern/cycles/kernel/geom/geom_curve.h
+++ b/intern/cycles/kernel/geom/geom_curve.h
@@ -152,48 +152,47 @@ ccl_device_inline void curvebounds(float *lower, float *upper, float *extremta,
 	float halfdiscroot = (p2 * p2 - 3 * p3 * p1);
 	float ta = -1.0f;
 	float tb = -1.0f;
+
 	*extremta = -1.0f;
 	*extremtb = -1.0f;
 	*upper = p0;
-	*lower = p0 + p1 + p2 + p3;
+	*lower = (p0 + p1) + (p2 + p3);
 	*extrema = *upper;
 	*extremb = *lower;
+
 	if(*lower >= *upper) {
 		*upper = *lower;
 		*lower = p0;
 	}
 
 	if(halfdiscroot >= 0) {
+		float inv3p3 = (1.0f/3.0f)/p3;
 		halfdiscroot = sqrt(halfdiscroot);
-		ta = (-p2 - halfdiscroot) / (3 * p3);
-		tb = (-p2 + halfdiscroot) / (3 * p3);
+		ta = (-p2 - halfdiscroot) * inv3p3;
+		tb = (-p2 + halfdiscroot) * inv3p3;
 	}
 
 	float t2;
 	float t3;
+
 	if(ta > 0.0f && ta < 1.0f) {
 		t2 = ta * ta;
 		t3 = t2 * ta;
 		*extremta = ta;
 		*extrema = p3 * t3 + p2 * t2 + p1 * ta + p0;
-		if(*extrema > *upper) {
-			*upper = *extrema;
-		}
-		if(*extrema < *lower) {
-			*lower = *extrema;
-		}
+
+		*upper = fmaxf(*extrema, *upper);
+		*lower = fminf(*extrema, *lower);
 	}
+
 	if(tb > 0.0f && tb < 1.0f) {
 		t2 = tb * tb;
 		t3 = t2 * tb;
 		*extremtb = tb;
 		*extremb = p3 * t3 + p2 * t2 + p1 * tb + p0;
-		if(*extremb >= *upper) {
-			*upper = *extremb;
-		}
-		if(*extremb <= *lower) {
-			*lower = *extremb;
-		}
+
+		*upper = fmaxf(*extremb, *upper);
+		*lower = fminf(*extremb, *lower);
 	}
 }
 
@@ -483,10 +482,11 @@ ccl_device_inline bool bvh_cardinal_curve_intersect(KernelGlobals *kg, Intersect
 					float d = sqrtf(p_curr.x * p_curr.x + p_curr.y * p_curr.y);
 					float d0 = d - r_curr;
 					float d1 = d + r_curr;
+					float inv_mw_extension = 1.0f/mw_extension;
 					if (d0 >= 0)
-						coverage = (min(d1 / mw_extension, 1.0f) - min(d0 / mw_extension, 1.0f)) * 0.5f;
+						coverage = (min(d1 * inv_mw_extension, 1.0f) - min(d0 * inv_mw_extension, 1.0f)) * 0.5f;
 					else // inside
-						coverage = (min(d1 / mw_extension, 1.0f) + min(-d0 / mw_extension, 1.0f)) * 0.5f;
+						coverage = (min(d1 * inv_mw_extension, 1.0f) + min(-d0 * inv_mw_extension, 1.0f)) * 0.5f;
 				}
 				
 				if (p_curr.x * p_curr.x + p_curr.y * p_curr.y >= r_ext * r_ext || p_curr.z <= epsilon || isect->t < p_curr.z) {
@@ -496,12 +496,19 @@ ccl_device_inline bool bvh_cardinal_curve_intersect(KernelGlobals *kg, Intersect
 				}
 
 				t = p_curr.z;
+
+				/* stochastic fade from minimum width */
+				if(difl != 0.0f && lcg_state) {
+					if(coverage != 1.0f && (lcg_step_float(lcg_state) > coverage))
+						return hit;
+				}
 			}
 			else {
 				float l = len(p_en - p_st);
 				/* minimum width extension */
 				float or1 = r1;
 				float or2 = r2;
+
 				if(difl != 0.0f) {
 					mw_extension = min(len(p_st - P) * difl, extmax);
 					or1 = r1 < mw_extension ? mw_extension : r1;
@@ -509,12 +516,14 @@ ccl_device_inline bool bvh_cardinal_curve_intersect(KernelGlobals *kg, Intersect
 					or2 = r2 < mw_extension ? mw_extension : r2;
 				}
 				/* --- */
-				float3 tg = (p_en - p_st) / l;
-				gd = (or2 - or1) / l;
+				float invl = 1.0f/l;
+				float3 tg = (p_en - p_st) * invl;
+				gd = (or2 - or1) * invl;
 				float difz = -dot(p_st,tg);
 				float cyla = 1.0f - (tg.z * tg.z * (1 + gd*gd));
+				float invcyla = 1.0f/cyla;
 				float halfb = (-p_st.z - tg.z*(difz + gd*(difz*gd + or1)));
-				float tcentre = -halfb/cyla;
+				float tcentre = -halfb*invcyla;
 				float zcentre = difz + (tg.z * tcentre);
 				float3 tdif = - p_st;
 				tdif.z += tcentre;
@@ -529,7 +538,7 @@ ccl_device_inline bool bvh_cardinal_curve_intersect(KernelGlobals *kg, Intersect
 				}
 				
 				float rootd = sqrtf(td);
-				float correction = ((-tb - rootd)/(2*cyla));
+				float correction = (-tb - rootd) * 0.5f * invcyla;
 				t = tcentre + correction;
 
 				float3 dp_st = (3 * curve_coef[3] * i_st + 2 * curve_coef[2]) * i_st + curve_coef[1];
@@ -540,7 +549,7 @@ ccl_device_inline bool bvh_cardinal_curve_intersect(KernelGlobals *kg, Intersect
 					dp_en *= -1;
 
 				if(flags & CURVE_KN_BACKFACING && (dot(dp_st, -p_st) + t * dp_st.z < 0 || dot(dp_en, p_en) - t * dp_en.z < 0 || isect->t < t || t <= 0.0f)) {
-					correction = ((-tb + rootd)/(2*cyla));
+					correction = (-tb + rootd) * 0.5f * invcyla;
 					t = tcentre + correction;
 				}			
 
@@ -550,22 +559,22 @@ ccl_device_inline bool bvh_cardinal_curve_intersect(KernelGlobals *kg, Intersect
 					continue;
 				}
 
-				float w = (zcentre + (tg.z * correction))/l;
+				float w = (zcentre + (tg.z * correction)) * invl;
 				w = clamp((float)w, 0.0f, 1.0f);
 				/* compute u on the curve segment */
 				u = i_st * (1 - w) + i_en * w;
-				r_curr = r1 + (r2 - r1) * w;
-				r_ext = or1 + (or2 - or1) * w;
-				coverage = r_curr/r_ext;
 
-			}
-			/* we found a new intersection */
+				/* stochastic fade from minimum width */
+				if(difl != 0.0f && lcg_state) {
+					r_curr = r1 + (r2 - r1) * w;
+					r_ext = or1 + (or2 - or1) * w;
+					coverage = r_curr/r_ext;
 
-			/* stochastic fade from minimum width */
-			if(lcg_state && coverage != 1.0f) {
-				if(lcg_step_float(lcg_state) > coverage)
-					return hit;
+					if(coverage != 1.0f && (lcg_step_float(lcg_state) > coverage))
+						return hit;
+				}
 			}
+			/* we found a new intersection */
 
 #ifdef __VISIBILITY_FLAG__
 			/* visibility flag test. we do it here under the assumption