Fix for slow deformation-motionblur in Cycles using the new spiral kink

mode.

This was caused by variation of the number of keys on child hairs due
to shortening of hair curves based on euclidian distances. The other
kink modes also shorten hairs, but use the parametric distance instead,
which does not vary with deformation of hairs.

1 files changed, 6 insertions, 13 deletions

diff --git a/source/blender/blenkernel/intern/particle_child.c b/source/blender/blenkernel/intern/particle_child.c
index 5bc79d132d5..fb877e44eb6 100644
--- a/source/blender/blenkernel/intern/particle_child.c
+++ b/source/blender/blenkernel/intern/particle_child.c
@@ -199,10 +199,11 @@ static void do_kink_spiral(ParticleThreadContext *ctx, ParticleTexture *ptex, co
 	float spiral_par_co[3] = {0.0f, 0.0f, 0.0f};
 	float spiral_par_vel[3] = {0.0f, 0.0f, 0.0f};
 	float spiral_par_rot[4] = {1.0f, 0.0f, 0.0f, 0.0f};
-	float len, totlen, cutlen;
+	float totlen;
+	float cut_time;
 	int start_index = 0, end_index = 0;
 	float kink_base[3];
-
+	
 	if (ptex) {
 		kink_amp *= ptex->kink_amp;
 		kink_freq *= ptex->kink_freq;
@@ -211,19 +212,12 @@ static void do_kink_spiral(ParticleThreadContext *ctx, ParticleTexture *ptex, co
 		rough_end *= ptex->roughe;
 	}
 	
-	totlen = 0.0f;
-	for (k = 0, key = keys; k < totkeys-1; k++, key++)
-		totlen += len_v3v3((key+1)->co, key->co);
-	
-	cutlen = max_ff(ptex->length * totlen - fabsf(kink_amp), 0.0f);
+	cut_time = (totkeys - 1) * ptex->length;
 	zero_v3(spiral_start);
 	
-	len = 0.0f;
 	for (k = 0, key = keys; k < totkeys-1; k++, key++) {
-		float seglen = len_v3v3((key+1)->co, key->co);
-		
-		if (seglen > 0.0f && len + seglen >= cutlen) {
-			float fac = (cutlen - len) / seglen;
+		if ((float)(k + 1) >= cut_time) {
+			float fac = cut_time - (float)k;
 			ParticleCacheKey *par = parent_keys + k;
 			
 			start_index = k + 1;
@@ -238,7 +232,6 @@ static void do_kink_spiral(ParticleThreadContext *ctx, ParticleTexture *ptex, co
 			
 			break;
 		}
-		len += seglen;
 	}
 	
 	zero_v3(dir);