[Impeller Scene] Change how property resolution works to fix Animation blending; add mutation log to nodes; enable backface culling; add vertex color contribution back to meshes (#38766)

* [Impeller Scene] Add mutation log to nodes

* Apply the bind pose matrix when the skin is initialized

* Refactor property resolver to modify decomposed properties

* Make the property resolvers additive again to support complex blending

* Normalize clip weights

* Fix UI-side animation bugs and add looping config

* Backface culling

* Make dart analyzer happy

* Incorporate vertex colors for imported meshes again

* Address comments

Author: bdero

ci/licenses_golden/licenses_flutter

@@ -1641,6 +1641,7 @@ ORIGIN: ../../../flutter/impeller/scene/animation/animation_clip.cc + ../../../f
 ORIGIN: ../../../flutter/impeller/scene/animation/animation_clip.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/scene/animation/animation_player.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/scene/animation/animation_player.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/scene/animation/animation_transforms.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/scene/animation/property_resolver.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/scene/animation/property_resolver.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/scene/camera.cc + ../../../flutter/LICENSE
@@ -4121,6 +4122,7 @@ FILE: ../../../flutter/impeller/scene/animation/animation_clip.cc
 FILE: ../../../flutter/impeller/scene/animation/animation_clip.h
 FILE: ../../../flutter/impeller/scene/animation/animation_player.cc
 FILE: ../../../flutter/impeller/scene/animation/animation_player.h
+FILE: ../../../flutter/impeller/scene/animation/animation_transforms.h
 FILE: ../../../flutter/impeller/scene/animation/property_resolver.cc
 FILE: ../../../flutter/impeller/scene/animation/property_resolver.h
 FILE: ../../../flutter/impeller/scene/camera.cc

impeller/geometry/quaternion.h

@@ -45,6 +45,8 @@ struct Quaternion {
     return {x * m, y * m, z * m, w * m};
   }
 
+  Quaternion Invert() const { return {-x, -y, -z, w}; }
+
   Quaternion Slerp(const Quaternion& to, double time) const;
 
   Quaternion operator*(const Quaternion& o) const {

impeller/scene/BUILD.gn

@@ -12,6 +12,7 @@ impeller_component("scene") {
     "animation/animation_clip.h",
     "animation/animation_player.cc",
     "animation/animation_player.h",
+    "animation/animation_transforms.h",
     "animation/property_resolver.cc",
     "animation/property_resolver.h",
     "camera.cc",

impeller/scene/animation/animation_clip.cc

@@ -67,7 +67,7 @@ Scalar AnimationClip::GetWeight() const {
 }
 
 void AnimationClip::SetWeight(Scalar weight) {
-  weight_ = weight;
+  weight_ = std::max(0.0f, weight);
 }
 
 SecondsF AnimationClip::GetPlaybackTime() const {
@@ -110,9 +110,16 @@ void AnimationClip::Advance(SecondsF delta_time) {
   }
 }
 
-void AnimationClip::ApplyToBindings() const {
+void AnimationClip::ApplyToBindings(
+    std::unordered_map<Node*, AnimationTransforms>& transform_decomps,
+    Scalar weight_multiplier) const {
   for (auto& binding : bindings_) {
-    binding.channel.resolver->Apply(*binding.node, playback_time_, weight_);
+    auto transforms = transform_decomps.find(binding.node);
+    if (transforms == transform_decomps.end()) {
+      continue;
+    }
+    binding.channel.resolver->Apply(transforms->second, playback_time_,
+                                    weight_ * weight_multiplier);
   }
 }
 

impeller/scene/animation/animation_clip.h

@@ -9,6 +9,7 @@
 
 #include "flutter/fml/macros.h"
 #include "impeller/scene/animation/animation.h"
+#include "impeller/scene/animation/animation_transforms.h"
 
 namespace impeller {
 namespace scene {
@@ -60,7 +61,9 @@ class AnimationClip final {
   void Advance(SecondsF delta_time);
 
   /// @brief  Applies the animation to all binded properties in the scene.
-  void ApplyToBindings() const;
+  void ApplyToBindings(
+      std::unordered_map<Node*, AnimationTransforms>& transform_decomps,
+      Scalar weight_multiplier) const;
 
  private:
   void BindToTarget(Node* node);

impeller/scene/animation/animation_player.cc

@@ -5,6 +5,7 @@
 #include "impeller/scene/animation/animation_player.h"
 
 #include <memory>
+#include <unordered_map>
 
 #include "flutter/fml/time/time_point.h"
 #include "impeller/base/timing.h"
@@ -19,20 +20,37 @@ AnimationPlayer::~AnimationPlayer() = default;
 AnimationPlayer::AnimationPlayer(AnimationPlayer&&) = default;
 AnimationPlayer& AnimationPlayer::operator=(AnimationPlayer&&) = default;
 
-AnimationClip& AnimationPlayer::AddAnimation(
-    std::shared_ptr<Animation> animation,
+AnimationClip* AnimationPlayer::AddAnimation(
+    const std::shared_ptr<Animation>& animation,
     Node* bind_target) {
-  AnimationClip clip(std::move(animation), bind_target);
+  if (!animation) {
+    VALIDATION_LOG << "Cannot add null animation.";
+    return nullptr;
+  }
+
+  AnimationClip clip(animation, bind_target);
 
   // Record all of the unique default transforms that this AnimationClip
   // will mutate.
   for (const auto& binding : clip.bindings_) {
-    default_target_transforms_.insert(
-        {binding.node, binding.node->GetLocalTransform()});
+    auto decomp = binding.node->GetLocalTransform().Decompose();
+    if (!decomp.has_value()) {
+      continue;
+    }
+    target_transforms_.insert(
+        {binding.node, AnimationTransforms{.bind_pose = decomp.value()}});
   }
 
-  clips_.push_back(std::move(clip));
-  return clips_.back();
+  auto result = clips_.insert({animation->GetName(), std::move(clip)});
+  return &result.first->second;
+}
+
+AnimationClip* AnimationPlayer::GetClip(const std::string& name) const {
+  auto result = clips_.find(name);
+  if (result == clips_.end()) {
+    return nullptr;
+  }
+  return const_cast<AnimationClip*>(&result->second);
 }
 
 void AnimationPlayer::Update() {
@@ -43,18 +61,27 @@ void AnimationPlayer::Update() {
   auto delta_time = new_time - previous_time_.value();
   previous_time_ = new_time;
 
-  Reset();
+  // Reset the animated pose state.
+  for (auto& [node, transforms] : target_transforms_) {
+    transforms.animated_pose = transforms.bind_pose;
+  }
+
+  // Compute a weight multiplier for normalizing the animation.
+  Scalar total_weight = 0;
+  for (auto& [_, clip] : clips_) {
+    total_weight += clip.GetWeight();
+  }
+  Scalar weight_multiplier = total_weight > 1 ? 1 / total_weight : 1;
 
-  // Update and apply all clips.
-  for (auto& clip : clips_) {
+  // Update and apply all clips to the animation pose state.
+  for (auto& [_, clip] : clips_) {
     clip.Advance(delta_time);
-    clip.ApplyToBindings();
+    clip.ApplyToBindings(target_transforms_, weight_multiplier);
   }
-}
 
-void AnimationPlayer::Reset() {
-  for (auto& [node, transform] : default_target_transforms_) {
-    node->SetLocalTransform(Matrix());
+  // Apply the animated pose to the bound joints.
+  for (auto& [node, transforms] : target_transforms_) {
+    node->SetLocalTransform(Matrix(transforms.animated_pose));
   }
 }
 

impeller/scene/animation/animation_player.h

@@ -4,16 +4,17 @@
 
 #pragma once
 
+#include <map>
 #include <memory>
 #include <optional>
-#include <unordered_map>
 #include <vector>
 
 #include "flutter/fml/hash_combine.h"
 #include "flutter/fml/macros.h"
 #include "flutter/fml/time/time_delta.h"
 #include "impeller/base/timing.h"
 #include "impeller/geometry/matrix.h"
+#include "impeller/geometry/matrix_decomposition.h"
 #include "impeller/scene/animation/animation_clip.h"
 
 namespace impeller {
@@ -29,19 +30,18 @@ class AnimationPlayer final {
   AnimationPlayer(AnimationPlayer&&);
   AnimationPlayer& operator=(AnimationPlayer&&);
 
-  AnimationClip& AddAnimation(std::shared_ptr<Animation> animation,
+  AnimationClip* AddAnimation(const std::shared_ptr<Animation>& animation,
                               Node* bind_target);
 
+  AnimationClip* GetClip(const std::string& name) const;
+
   /// @brief  Advanced all clips and updates animated properties in the scene.
   void Update();
 
-  /// @brief  Reset all bound animation target transforms.
-  void Reset();
-
  private:
-  std::unordered_map<Node*, Matrix> default_target_transforms_;
+  std::unordered_map<Node*, AnimationTransforms> target_transforms_;
 
-  std::vector<AnimationClip> clips_;
+  std::map<std::string, AnimationClip> clips_;
 
   std::optional<TimePoint> previous_time_;
 

impeller/scene/animation/animation_transforms.h

@@ -0,0 +1,18 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#pragma once
+
+#include "impeller/geometry/matrix_decomposition.h"
+
+namespace impeller {
+namespace scene {
+
+struct AnimationTransforms {
+  MatrixDecomposition bind_pose;
+  MatrixDecomposition animated_pose;
+};
+
+}  // namespace scene
+}  // namespace impeller

impeller/scene/animation/property_resolver.cc

@@ -8,6 +8,7 @@
 #include <iterator>
 #include <memory>
 
+#include "impeller/geometry/matrix_decomposition.h"
 #include "impeller/geometry/point.h"
 #include "impeller/scene/node.h"
 
@@ -78,7 +79,7 @@ TranslationTimelineResolver::TranslationTimelineResolver() = default;
 
 TranslationTimelineResolver::~TranslationTimelineResolver() = default;
 
-void TranslationTimelineResolver::Apply(Node& target,
+void TranslationTimelineResolver::Apply(AnimationTransforms& target,
                                         SecondsF time,
                                         Scalar weight) {
   if (values_.empty()) {
@@ -89,15 +90,16 @@ void TranslationTimelineResolver::Apply(Node& target,
   if (key.lerp < 1) {
     value = values_[key.index - 1].Lerp(value, key.lerp);
   }
-  target.SetLocalTransform(target.GetLocalTransform() *
-                           Matrix::MakeTranslation(value * weight));
+
+  target.animated_pose.translation +=
+      (value - target.bind_pose.translation) * weight;
 }
 
 RotationTimelineResolver::RotationTimelineResolver() = default;
 
 RotationTimelineResolver::~RotationTimelineResolver() = default;
 
-void RotationTimelineResolver::Apply(Node& target,
+void RotationTimelineResolver::Apply(AnimationTransforms& target,
                                      SecondsF time,
                                      Scalar weight) {
   if (values_.empty()) {
@@ -108,15 +110,19 @@ void RotationTimelineResolver::Apply(Node& target,
   if (key.lerp < 1) {
     value = values_[key.index - 1].Slerp(value, key.lerp);
   }
-  target.SetLocalTransform(target.GetLocalTransform() *
-                           Matrix::MakeRotation(value * weight));
+
+  target.animated_pose.rotation =
+      target.animated_pose.rotation *
+      Quaternion().Slerp(target.bind_pose.rotation.Invert() * value, weight);
 }
 
 ScaleTimelineResolver::ScaleTimelineResolver() = default;
 
 ScaleTimelineResolver::~ScaleTimelineResolver() = default;
 
-void ScaleTimelineResolver::Apply(Node& target, SecondsF time, Scalar weight) {
+void ScaleTimelineResolver::Apply(AnimationTransforms& target,
+                                  SecondsF time,
+                                  Scalar weight) {
   if (values_.empty()) {
     return;
   }
@@ -125,8 +131,9 @@ void ScaleTimelineResolver::Apply(Node& target, SecondsF time, Scalar weight) {
   if (key.lerp < 1) {
     value = values_[key.index - 1].Lerp(value, key.lerp);
   }
-  target.SetLocalTransform(target.GetLocalTransform() *
-                           Matrix::MakeScale(value * weight));
+
+  target.animated_pose.scale *=
+      Vector3(1, 1, 1).Lerp(value / target.bind_pose.scale, weight);
 }
 
 }  // namespace scene

impeller/scene/animation/property_resolver.h

@@ -11,9 +11,11 @@
 #include "flutter/fml/hash_combine.h"
 #include "flutter/fml/macros.h"
 #include "impeller/base/timing.h"
+#include "impeller/geometry/matrix_decomposition.h"
 #include "impeller/geometry/quaternion.h"
 #include "impeller/geometry/scalar.h"
 #include "impeller/geometry/vector.h"
+#include "impeller/scene/animation/animation_transforms.h"
 
 namespace impeller {
 namespace scene {
@@ -46,7 +48,9 @@ class PropertyResolver {
   ///         many different PropertyResolvers prior to rendering. For example,
   ///         an AnimationPlayer may blend multiple Animations together by
   ///         applying several AnimationClips.
-  virtual void Apply(Node& target, SecondsF time, Scalar weight) = 0;
+  virtual void Apply(AnimationTransforms& target,
+                     SecondsF time,
+                     Scalar weight) = 0;
 };
 
 class TimelineResolver : public PropertyResolver {
@@ -74,7 +78,9 @@ class TranslationTimelineResolver final : public TimelineResolver {
   ~TranslationTimelineResolver();
 
   // |Resolver|
-  void Apply(Node& target, SecondsF time, Scalar weight) override;
+  void Apply(AnimationTransforms& target,
+             SecondsF time,
+             Scalar weight) override;
 
  private:
   TranslationTimelineResolver();
@@ -91,7 +97,9 @@ class RotationTimelineResolver final : public TimelineResolver {
   ~RotationTimelineResolver();
 
   // |Resolver|
-  void Apply(Node& target, SecondsF time, Scalar weight) override;
+  void Apply(AnimationTransforms& target,
+             SecondsF time,
+             Scalar weight) override;
 
  private:
   RotationTimelineResolver();
@@ -108,7 +116,9 @@ class ScaleTimelineResolver final : public TimelineResolver {
   ~ScaleTimelineResolver();
 
   // |Resolver|
-  void Apply(Node& target, SecondsF time, Scalar weight) override;
+  void Apply(AnimationTransforms& target,
+             SecondsF time,
+             Scalar weight) override;
 
  private:
   ScaleTimelineResolver();