Fix for [#34099] Particles leaking from moving meshes

This was caused by a floating point precision error. During collision detection, Newton-Raphson iteration is used to find the exact time of the collision. But when using subframes, the initial Newton step was too small. Now the initial step is given in absolute units. When subframes = 0, this should behave almost the same as before.

Thanks to Janne Karhu, Lukas Toenne and Ton Roosendaal for their help with this patch, and to AutoCRC for funding.

1 files changed, 4 insertions, 1 deletions

diff --git a/source/blender/blenkernel/BKE_particle.h b/source/blender/blenkernel/BKE_particle.h
index a9a8bc32064..6c207675cb1 100644
--- a/source/blender/blenkernel/BKE_particle.h
+++ b/source/blender/blenkernel/BKE_particle.h
@@ -220,7 +220,10 @@ typedef struct ParticleCollision {
 
 	ParticleCollisionElement pce;
 
-	float total_time, inv_timestep;
+	/* total_time is the amount of time in this subframe
+	 * inv_total_time is the opposite
+	 * inv_timestep is the inverse of the amount of time in this frame */
+	float total_time, inv_total_time, inv_timestep;
 
 	float radius;
 	float co1[3], co2[3];