From 658fd8df0bd2427cd77e7fc4bcca8a102f67b626 Mon Sep 17 00:00:00 2001
From: Jacques Lucke <jacques@blender.org>
Date: Fri, 26 Nov 2021 11:05:47 +0100
Subject: Geometry Nodes: refactor multi-threading in field evaluation

Previously, there was a fixed grain size for all multi-functions. That was
not sufficient because some functions could benefit a lot from smaller
grain sizes.

This refactors adds a new `MultiFunction::call_auto` method which has the
same effect as just calling `MultiFunction::call` but additionally figures
out how to execute the specific multi-function efficiently. It determines
a good grain size and decides whether the mask indices should be shifted
or not.

Most multi-function evaluations benefit from this, but medium sized work
loads (1000 - 50000 elements) benefit from it the most. Especially when
expensive multi-functions (e.g. noise) is involved. This is because for
smaller work loads, threading is rarely used and for larger work loads
threading worked fine before already.

With this patch, multi-functions can specify execution hints, that allow
the caller to execute it most efficiently. These execution hints still
have to be added to more functions.

Some performance measurements of a field evaluation involving noise and
math nodes, ordered by the number of elements being evaluated:
```
1,000,000: 133 ms   -> 120 ms
  100,000:  30 ms   ->  18 ms
   10,000:  20 ms   ->   2.7 ms
    1,000:   4 ms   ->   0.5 ms
      100:   0.5 ms ->   0.4 ms
```
---
 .../geometry/nodes/node_geo_transfer_attribute.cc     |  8 ++++----
 .../nodes/shader/nodes/node_shader_tex_noise.cc       |  8 ++++++++
 .../nodes/shader/nodes/node_shader_tex_voronoi.cc     | 19 ++++++++++++++++++-
 3 files changed, 30 insertions(+), 5 deletions(-)

(limited to 'source/blender/nodes')

diff --git a/source/blender/nodes/geometry/nodes/node_geo_transfer_attribute.cc b/source/blender/nodes/geometry/nodes/node_geo_transfer_attribute.cc
index acd8e6cad25..dc5118a56c7 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_transfer_attribute.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_transfer_attribute.cc
@@ -131,9 +131,9 @@ static void get_closest_in_bvhtree(BVHTreeFromMesh &tree_data,
                                    const MutableSpan<float> r_distances_sq,
                                    const MutableSpan<float3> r_positions)
 {
-  BLI_assert(positions.size() == r_indices.size() || r_indices.is_empty());
-  BLI_assert(positions.size() == r_distances_sq.size() || r_distances_sq.is_empty());
-  BLI_assert(positions.size() == r_positions.size() || r_positions.is_empty());
+  BLI_assert(positions.size() >= r_indices.size());
+  BLI_assert(positions.size() >= r_distances_sq.size());
+  BLI_assert(positions.size() >= r_positions.size());
 
   for (const int i : mask) {
     BVHTreeNearest nearest;
@@ -159,7 +159,7 @@ static void get_closest_pointcloud_points(const PointCloud &pointcloud,
                                           const MutableSpan<int> r_indices,
                                           const MutableSpan<float> r_distances_sq)
 {
-  BLI_assert(positions.size() == r_indices.size());
+  BLI_assert(positions.size() >= r_indices.size());
   BLI_assert(pointcloud.totpoint > 0);
 
   BVHTreeFromPointCloud tree_data;
diff --git a/source/blender/nodes/shader/nodes/node_shader_tex_noise.cc b/source/blender/nodes/shader/nodes/node_shader_tex_noise.cc
index 7dd2695ecf7..5f846207673 100644
--- a/source/blender/nodes/shader/nodes/node_shader_tex_noise.cc
+++ b/source/blender/nodes/shader/nodes/node_shader_tex_noise.cc
@@ -229,6 +229,14 @@ class NoiseFunction : public fn::MultiFunction {
       }
     }
   }
+
+  ExecutionHints get_execution_hints() const override
+  {
+    ExecutionHints hints;
+    hints.allocates_array = false;
+    hints.min_grain_size = 100;
+    return hints;
+  }
 };
 
 static void sh_node_noise_build_multi_function(blender::nodes::NodeMultiFunctionBuilder &builder)
diff --git a/source/blender/nodes/shader/nodes/node_shader_tex_voronoi.cc b/source/blender/nodes/shader/nodes/node_shader_tex_voronoi.cc
index 1bc3741d27c..5d2654f61c8 100644
--- a/source/blender/nodes/shader/nodes/node_shader_tex_voronoi.cc
+++ b/source/blender/nodes/shader/nodes/node_shader_tex_voronoi.cc
@@ -167,6 +167,8 @@ static void node_shader_update_tex_voronoi(bNodeTree *ntree, bNode *node)
 
 namespace blender::nodes {
 
+static MultiFunction::ExecutionHints voronoi_execution_hints{50, false};
+
 class VoronoiMinowskiFunction : public fn::MultiFunction {
  private:
   int dimensions_;
@@ -592,6 +594,11 @@ class VoronoiMinowskiFunction : public fn::MultiFunction {
       }
     }
   }
+
+  ExecutionHints get_execution_hints() const override
+  {
+    return voronoi_execution_hints;
+  }
 };
 
 class VoronoiMetricFunction : public fn::MultiFunction {
@@ -1106,6 +1113,11 @@ class VoronoiMetricFunction : public fn::MultiFunction {
       }
     }
   }
+
+  ExecutionHints get_execution_hints() const override
+  {
+    return voronoi_execution_hints;
+  }
 };
 
 class VoronoiEdgeFunction : public fn::MultiFunction {
@@ -1282,7 +1294,12 @@ class VoronoiEdgeFunction : public fn::MultiFunction {
         break;
       }
     }
-  };
+  }
+
+  ExecutionHints get_execution_hints() const override
+  {
+    return voronoi_execution_hints;
+  }
 };
 
 static void sh_node_voronoi_build_multi_function(blender::nodes::NodeMultiFunctionBuilder &builder)
-- 
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