From 34d553671daeb5f38d8bbc69ebbdee0f93421000 Mon Sep 17 00:00:00 2001
From: Olivier Maury <omaury>
Date: Fri, 7 Jan 2022 17:15:37 +0100
Subject: Fix wrong shadow terminator geometry offset with deformation motion
 blur

Differential Revision: https://developer.blender.org/D13759
---
 intern/cycles/kernel/geom/motion_triangle.h | 46 +++++++++++++++++++++++++++++
 intern/cycles/kernel/light/sample.h         |  9 +++++-
 2 files changed, 54 insertions(+), 1 deletion(-)

(limited to 'intern')

diff --git a/intern/cycles/kernel/geom/motion_triangle.h b/intern/cycles/kernel/geom/motion_triangle.h
index 62b7b630c89..bd62325eaf2 100644
--- a/intern/cycles/kernel/geom/motion_triangle.h
+++ b/intern/cycles/kernel/geom/motion_triangle.h
@@ -116,6 +116,52 @@ ccl_device_inline void motion_triangle_vertices(
   verts[2] = (1.0f - t) * verts[2] + t * next_verts[2];
 }
 
+ccl_device_inline void motion_triangle_vertices_and_normals(
+    KernelGlobals kg, int object, int prim, float time, float3 verts[3], float3 normals[3])
+{
+  /* get motion info */
+  int numsteps, numverts;
+  object_motion_info(kg, object, &numsteps, &numverts, NULL);
+
+  /* Figure out which steps we need to fetch and their interpolation factor. */
+  int maxstep = numsteps * 2;
+  int step = min((int)(time * maxstep), maxstep - 1);
+  float t = time * maxstep - step;
+
+  /* Find attribute. */
+  int offset = intersection_find_attribute(kg, object, ATTR_STD_MOTION_VERTEX_POSITION);
+  kernel_assert(offset != ATTR_STD_NOT_FOUND);
+
+  /* Fetch vertex coordinates. */
+  float3 next_verts[3];
+  uint4 tri_vindex = kernel_tex_fetch(__tri_vindex, prim);
+
+  motion_triangle_verts_for_step(kg, tri_vindex, offset, numverts, numsteps, step, verts);
+  motion_triangle_verts_for_step(kg, tri_vindex, offset, numverts, numsteps, step + 1, next_verts);
+
+  /* Interpolate between steps. */
+  verts[0] = (1.0f - t) * verts[0] + t * next_verts[0];
+  verts[1] = (1.0f - t) * verts[1] + t * next_verts[1];
+  verts[2] = (1.0f - t) * verts[2] + t * next_verts[2];
+
+  /* Compute smooth normal. */
+
+  /* Find attribute. */
+  offset = intersection_find_attribute(kg, object, ATTR_STD_MOTION_VERTEX_NORMAL);
+  kernel_assert(offset != ATTR_STD_NOT_FOUND);
+
+  /* Fetch vertex coordinates. */
+  float3 next_normals[3];
+  motion_triangle_normals_for_step(kg, tri_vindex, offset, numverts, numsteps, step, normals);
+  motion_triangle_normals_for_step(
+      kg, tri_vindex, offset, numverts, numsteps, step + 1, next_normals);
+
+  /* Interpolate between steps. */
+  normals[0] = (1.0f - t) * normals[0] + t * next_normals[0];
+  normals[1] = (1.0f - t) * normals[1] + t * next_normals[1];
+  normals[2] = (1.0f - t) * normals[2] + t * next_normals[2];
+}
+
 ccl_device_inline float3 motion_triangle_smooth_normal(
     KernelGlobals kg, float3 Ng, int object, int prim, float u, float v, float time)
 {
diff --git a/intern/cycles/kernel/light/sample.h b/intern/cycles/kernel/light/sample.h
index 5a4b7c0a302..7dbc783b1bb 100644
--- a/intern/cycles/kernel/light/sample.h
+++ b/intern/cycles/kernel/light/sample.h
@@ -141,7 +141,14 @@ ccl_device_inline float3 shadow_ray_smooth_surface_offset(
     KernelGlobals kg, ccl_private const ShaderData *ccl_restrict sd, float3 Ng)
 {
   float3 V[3], N[3];
-  triangle_vertices_and_normals(kg, sd->prim, V, N);
+
+  if (sd->type == PRIMITIVE_MOTION_TRIANGLE) {
+    motion_triangle_vertices_and_normals(kg, sd->object, sd->prim, sd->time, V, N);
+  }
+  else {
+    kernel_assert(sd->type == PRIMITIVE_TRIANGLE);
+    triangle_vertices_and_normals(kg, sd->prim, V, N);
+  }
 
   const float u = sd->u, v = sd->v;
   const float w = 1 - u - v;
-- 
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