Attribute Math: Improve performance of mixer in some cases

The `DefaultMixer` for mixing generic data types has some issues:
1. The full buffer is always zeroed, even if only some is used.
2. Finalizing also works on all values, even if only some are used.
3. "mixing" doesn't allow setting the first value, requiring that
everything is cleared beforehand.

This commit adds the following functionality:
1. Constructor with the specified `IndexMask` for preliminary zeroing.
2. `set` method to overwrite the value.
3. `finalize` with the specified mask to process a subset of values.

This is useful in situations where you want to use the
DefaultMixer without having to overwrite all the values many times.

A performance improvement was observed for NURBS curve evaluation and
attribute interpolation from the point to curve domain of about 15% and
35% respectively (100,000 curves).

Differential Revision: https://developer.blender.org/D15434

1 files changed, 90 insertions, 7 deletions

diff --git a/source/blender/blenkernel/BKE_attribute_math.hh b/source/blender/blenkernel/BKE_attribute_math.hh
index 01c2ef988f2..0a8e013abf2 100644
--- a/source/blender/blenkernel/BKE_attribute_math.hh
+++ b/source/blender/blenkernel/BKE_attribute_math.hh
@@ -188,10 +188,28 @@ template<typename T> class SimpleMixer {
    * \param default_value: Output value for an element that has not been affected by a #mix_in.
    */
   SimpleMixer(MutableSpan<T> buffer, T default_value = {})
+      : SimpleMixer(buffer, buffer.index_range(), default_value)
+  {
+  }
+
+  /**
+   * \param mask: Only initialize these indices. Other indices in the buffer will be invalid.
+   */
+  SimpleMixer(MutableSpan<T> buffer, const IndexMask mask, T default_value = {})
       : buffer_(buffer), default_value_(default_value), total_weights_(buffer.size(), 0.0f)
   {
     BLI_STATIC_ASSERT(std::is_trivial_v<T>, "");
-    memset(buffer_.data(), 0, sizeof(T) * buffer_.size());
+    mask.foreach_index([&](const int64_t i) { buffer_[i] = default_value_; });
+  }
+
+  /**
+   * Set a #value into the element with the given #index.
+   */
+  void set(const int64_t index, const T &value, const float weight = 1.0f)
+  {
+    BLI_assert(weight >= 0.0f);
+    buffer_[index] = value * weight;
+    total_weights_[index] = weight;
   }
 
   /**
@@ -209,7 +227,12 @@ template<typename T> class SimpleMixer {
    */
   void finalize()
   {
-    for (const int64_t i : buffer_.index_range()) {
+    this->finalize(IndexMask(buffer_.size()));
+  }
+
+  void finalize(const IndexMask mask)
+  {
+    mask.foreach_index([&](const int64_t i) {
       const float weight = total_weights_[i];
       if (weight > 0.0f) {
         buffer_[i] *= 1.0f / weight;
@@ -217,7 +240,7 @@ template<typename T> class SimpleMixer {
       else {
         buffer_[i] = default_value_;
       }
-    }
+    });
   }
 };
 
@@ -237,9 +260,25 @@ class BooleanPropagationMixer {
   /**
    * \param buffer: Span where the interpolated values should be stored.
    */
-  BooleanPropagationMixer(MutableSpan<bool> buffer) : buffer_(buffer)
+  BooleanPropagationMixer(MutableSpan<bool> buffer)
+      : BooleanPropagationMixer(buffer, buffer.index_range())
+  {
+  }
+
+  /**
+   * \param mask: Only initialize these indices. Other indices in the buffer will be invalid.
+   */
+  BooleanPropagationMixer(MutableSpan<bool> buffer, const IndexMask mask) : buffer_(buffer)
+  {
+    mask.foreach_index([&](const int64_t i) { buffer_[i] = false; });
+  }
+
+  /**
+   * Set a #value into the element with the given #index.
+   */
+  void set(const int64_t index, const bool value, [[maybe_unused]] const float weight = 1.0f)
   {
-    buffer_.fill(false);
+    buffer_[index] = value;
   }
 
   /**
@@ -256,6 +295,10 @@ class BooleanPropagationMixer {
   void finalize()
   {
   }
+
+  void finalize(const IndexMask /*mask*/)
+  {
+  }
 };
 
 /**
@@ -277,8 +320,27 @@ class SimpleMixerWithAccumulationType {
 
  public:
   SimpleMixerWithAccumulationType(MutableSpan<T> buffer, T default_value = {})
+      : SimpleMixerWithAccumulationType(buffer, buffer.index_range(), default_value)
+  {
+  }
+
+  /**
+   * \param mask: Only initialize these indices. Other indices in the buffer will be invalid.
+   */
+  SimpleMixerWithAccumulationType(MutableSpan<T> buffer,
+                                  const IndexMask mask,
+                                  T default_value = {})
       : buffer_(buffer), default_value_(default_value), accumulation_buffer_(buffer.size())
   {
+    mask.foreach_index([&](const int64_t index) { buffer_[index] = default_value_; });
+  }
+
+  void set(const int64_t index, const T &value, const float weight = 1.0f)
+  {
+    const AccumulationT converted_value = static_cast<AccumulationT>(value);
+    Item &item = accumulation_buffer_[index];
+    item.value = converted_value * weight;
+    item.weight = weight;
   }
 
   void mix_in(const int64_t index, const T &value, const float weight = 1.0f)
@@ -291,7 +353,12 @@ class SimpleMixerWithAccumulationType {
 
   void finalize()
   {
-    for (const int64_t i : buffer_.index_range()) {
+    this->finalize(buffer_.index_range());
+  }
+
+  void finalize(const IndexMask mask)
+  {
+    mask.foreach_index([&](const int64_t i) {
       const Item &item = accumulation_buffer_[i];
       if (item.weight > 0.0f) {
         const float weight_inv = 1.0f / item.weight;
@@ -301,7 +368,7 @@ class SimpleMixerWithAccumulationType {
       else {
         buffer_[i] = default_value_;
       }
-    }
+    });
   }
 };
 
@@ -314,8 +381,16 @@ class ColorGeometry4fMixer {
  public:
   ColorGeometry4fMixer(MutableSpan<ColorGeometry4f> buffer,
                        ColorGeometry4f default_color = ColorGeometry4f(0.0f, 0.0f, 0.0f, 1.0f));
+  /**
+   * \param mask: Only initialize these indices. Other indices in the buffer will be invalid.
+   */
+  ColorGeometry4fMixer(MutableSpan<ColorGeometry4f> buffer,
+                       IndexMask mask,
+                       ColorGeometry4f default_color = ColorGeometry4f(0.0f, 0.0f, 0.0f, 1.0f));
+  void set(int64_t index, const ColorGeometry4f &color, float weight = 1.0f);
   void mix_in(int64_t index, const ColorGeometry4f &color, float weight = 1.0f);
   void finalize();
+  void finalize(IndexMask mask);
 };
 
 class ColorGeometry4bMixer {
@@ -328,8 +403,16 @@ class ColorGeometry4bMixer {
  public:
   ColorGeometry4bMixer(MutableSpan<ColorGeometry4b> buffer,
                        ColorGeometry4b default_color = ColorGeometry4b(0, 0, 0, 255));
+  /**
+   * \param mask: Only initialize these indices. Other indices in the buffer will be invalid.
+   */
+  ColorGeometry4bMixer(MutableSpan<ColorGeometry4b> buffer,
+                       IndexMask mask,
+                       ColorGeometry4b default_color = ColorGeometry4b(0, 0, 0, 255));
+  void set(int64_t index, const ColorGeometry4b &color, float weight = 1.0f);
   void mix_in(int64_t index, const ColorGeometry4b &color, float weight = 1.0f);
   void finalize();
+  void finalize(IndexMask mask);
 };
 
 template<typename T> struct DefaultMixerStruct {