[Bf-blender-cvs] [8047aec] compositor-2016: Fix T48571: Cycles/GPU - A lot of fireflies on SSS+Volume

[Sergey Sharybin]

Commit: 8047aecf4bd713070646c521859fd13d3f6919db
Author: Sergey Sharybin
Date:   Mon Jun 6 15:56:22 2016 +0200
Branches: compositor-2016
https://developer.blender.org/rB8047aecf4bd713070646c521859fd13d3f6919db

Fix T48571: Cycles/GPU - A lot of fireflies on SSS+Volume

Was some accumulated precision error happening.

===================================================================

M	intern/cycles/kernel/kernel_volume.h

===================================================================

diff --git a/intern/cycles/kernel/kernel_volume.h b/intern/cycles/kernel/kernel_volume.h
index e1ea60f..0e313b8 100644
--- a/intern/cycles/kernel/kernel_volume.h
+++ b/intern/cycles/kernel/kernel_volume.h
@@ -1216,6 +1216,7 @@ ccl_device void kernel_volume_stack_update_for_subsurface(KernelGlobals *kg,
 #  else
 	Intersection isect;
 	int step = 0;
+	float3 Pend = ray->P + ray->D*ray->t;
 	while(step < 2 * VOLUME_STACK_SIZE &&
 	      scene_intersect_volume(kg,
 	                             &volume_ray,
@@ -1227,7 +1228,9 @@ ccl_device void kernel_volume_stack_update_for_subsurface(KernelGlobals *kg,
 
 		/* Move ray forward. */
 		volume_ray.P = ray_offset(stack_sd->P, -stack_sd->Ng);
-		volume_ray.t -= stack_sd->ray_length;
+		if(volume_ray.t != FLT_MAX) {
+			volume_ray.D = normalize_len(Pend - volume_ray.P, &volume_ray.t);
+		}
 		++step;
 	}
 #  endif