[vr] Avoid some unnecessary work in UpdateWorldSpaceTransforms

Previously, we would do the local update unconditionally. With this
change, we keep track of a dirty bit for the world space transform as
well as a baked version of the local transform so we don't need to
call cc::TransformOperations::Apply repeatedly to realize the same
results.

Some elements have special conditions for the dirtiness of their local
transform, so I have also created a ShouldUpdateWorldSpaceTransform
function so that subclasses can customize this behavior. The reticle,
for example, is always dirty.

Bug: 828684
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_vr;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I5b581a72d7caa39d47dcdc686d212879b3da3093
Reviewed-on: https://chromium-review.googlesource.com/995573Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Commit-Queue: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548075}

chrome/browser/vr/elements/controller.h

@@ -21,6 +21,7 @@ class Controller : public UiElement {
 
   void set_local_transform(const gfx::Transform& transform) {
     local_transform_ = transform;
+    set_world_space_transform_dirty();
   }
 
   class Renderer : public BaseRenderer {

chrome/browser/vr/elements/repositioner.cc

@@ -65,9 +65,12 @@ void Repositioner::SetEnabled(bool enabled) {
 
 void Repositioner::Reset() {
   transform_.MakeIdentity();
+  set_world_space_transform_dirty();
 }
 
 void Repositioner::UpdateTransform(const gfx::Transform& head_pose) {
+  set_world_space_transform_dirty();
+
   gfx::Vector3dF head_up = vr::GetUpVector(head_pose);
   gfx::Vector3dF head_forward = vr::GetForwardVector(head_pose);
 

chrome/browser/vr/elements/resizer.cc

@@ -56,6 +56,7 @@ void Resizer::SetEnabled(bool enabled) {
 
 void Resizer::Reset() {
   transform_.MakeIdentity();
+  set_world_space_transform_dirty();
   t_ = initial_t_ = kDefaultFraction;
 }
 
@@ -66,6 +67,7 @@ void Resizer::UpdateTransform(const gfx::Transform& head_pose) {
       gfx::Tween::FloatValueBetween(t_, kMinResizerScale, kMaxResizerScale);
   transform_.MakeIdentity();
   transform_.Scale(scale, scale);
+  set_world_space_transform_dirty();
 }
 
 bool Resizer::OnBeginFrame(const base::TimeTicks& time,

chrome/browser/vr/elements/reticle.cc

@@ -183,4 +183,9 @@ gfx::Transform Reticle::GetTargetLocalTransform() const {
   return LocalTransform();
 }
 
+bool Reticle::ShouldUpdateWorldSpaceTransform(
+    bool parent_transform_changed) const {
+  return true;
+}
+
 }  // namespace vr

chrome/browser/vr/elements/reticle.h

@@ -49,6 +49,8 @@ class Reticle : public UiElement {
               const CameraModel& model) const final;
   gfx::Transform LocalTransform() const final;
   gfx::Transform GetTargetLocalTransform() const final;
+  bool ShouldUpdateWorldSpaceTransform(
+      bool parent_transform_changed) const final;
 
   gfx::Point3F origin_;
   gfx::Point3F target_;

chrome/browser/vr/elements/scaled_depth_adjuster.cc

@@ -45,6 +45,7 @@ bool ScaledDepthAdjuster::OnBeginFrame(const base::TimeTicks& time,
   float z = -o.z() + delta_z_;
   transform_.Scale3d(z, z, z);
   transform_.Translate3d(0, 0, -1);
+  set_world_space_transform_dirty();
   return true;
 }
 

chrome/browser/vr/elements/ui_element.cc

@@ -302,15 +302,29 @@ void UiElement::SetLayoutOffset(float x, float y) {
   } else if (y_centering() == BOTTOM) {
     y += size_.height() / 2;
   }
+
+  if (x == layout_offset_.at(0).translate.x &&
+      y == layout_offset_.at(0).translate.y &&
+      !IsAnimatingProperty(LAYOUT_OFFSET)) {
+    return;
+  }
+
   cc::TransformOperations operations = layout_offset_;
   cc::TransformOperation& op = operations.at(0);
   op.translate = {x, y, 0};
   op.Bake();
   animation_.TransitionTransformOperationsTo(last_frame_time_, LAYOUT_OFFSET,
-                                             transform_operations_, operations);
+                                             layout_offset_, operations);
 }
 
 void UiElement::SetTranslate(float x, float y, float z) {
+  if (x == transform_operations_.at(kTranslateIndex).translate.x &&
+      y == transform_operations_.at(kTranslateIndex).translate.y &&
+      z == transform_operations_.at(kTranslateIndex).translate.z &&
+      !IsAnimatingProperty(TRANSFORM)) {
+    return;
+  }
+
   cc::TransformOperations operations = transform_operations_;
   cc::TransformOperation& op = operations.at(kTranslateIndex);
   op.translate = {x, y, z};
@@ -320,16 +334,33 @@ void UiElement::SetTranslate(float x, float y, float z) {
 }
 
 void UiElement::SetRotate(float x, float y, float z, float radians) {
+  float degrees = gfx::RadToDeg(radians);
+
+  if (x == transform_operations_.at(kRotateIndex).rotate.axis.x &&
+      y == transform_operations_.at(kRotateIndex).rotate.axis.y &&
+      z == transform_operations_.at(kRotateIndex).rotate.axis.z &&
+      degrees == transform_operations_.at(kRotateIndex).rotate.angle &&
+      !IsAnimatingProperty(TRANSFORM)) {
+    return;
+  }
+
   cc::TransformOperations operations = transform_operations_;
   cc::TransformOperation& op = operations.at(kRotateIndex);
   op.rotate.axis = {x, y, z};
-  op.rotate.angle = gfx::RadToDeg(radians);
+  op.rotate.angle = degrees;
   op.Bake();
   animation_.TransitionTransformOperationsTo(last_frame_time_, TRANSFORM,
                                              transform_operations_, operations);
 }
 
 void UiElement::SetScale(float x, float y, float z) {
+  if (x == transform_operations_.at(kScaleIndex).scale.x &&
+      y == transform_operations_.at(kScaleIndex).scale.y &&
+      z == transform_operations_.at(kScaleIndex).scale.z &&
+      !IsAnimatingProperty(TRANSFORM)) {
+    return;
+  }
+
   cc::TransformOperations operations = transform_operations_;
   cc::TransformOperation& op = operations.at(kScaleIndex);
   op.scale = {x, y, z};
@@ -654,12 +685,17 @@ void UiElement::NotifyClientTransformOperationsAnimated(
   } else {
     NOTREACHED();
   }
+  local_transform_ = layout_offset_.Apply() * transform_operations_.Apply();
+  world_space_transform_dirty_ = true;
 }
 
 void UiElement::NotifyClientSizeAnimated(const gfx::SizeF& size,
                                          int target_property_id,
                                          cc::KeyframeModel* keyframe_model) {
+  if (size_ == size)
+    return;
   size_ = size;
+  world_space_transform_dirty_ = true;
 }
 
 void UiElement::SetTransitionedProperties(
@@ -747,7 +783,10 @@ void UiElement::DoLayOutChildren() {
   bounds.Inset(-left_padding_, -bottom_padding_, -right_padding_,
                -top_padding_);
   bounds.set_origin(bounds.CenterPoint());
-  local_origin_ = bounds.origin();
+  if (local_origin_ != bounds.origin()) {
+    world_space_transform_dirty_ = true;
+    local_origin_ = bounds.origin();
+  }
   if (bounds.size() == GetTargetSize())
     return;
 
@@ -801,35 +840,40 @@ void UiElement::UpdateComputedOpacity() {
   updated_visibility_this_frame_ = IsVisible() != was_visible;
 }
 
-void UiElement::UpdateWorldSpaceTransformRecursive() {
-  gfx::Transform transform;
-  transform.Translate(local_origin_.x(), local_origin_.y());
-  if (!size_.IsEmpty()) {
-    transform.Scale(size_.width(), size_.height());
-  }
+void UiElement::UpdateWorldSpaceTransformRecursive(bool parent_changed) {
+  bool changed = false;
+  if (ShouldUpdateWorldSpaceTransform(parent_changed)) {
+    gfx::Transform transform;
+    transform.Translate(local_origin_.x(), local_origin_.y());
 
-  // Compute an inheritable transformation that can be applied to this element,
-  // and it's children, if applicable.
-  gfx::Transform inheritable = LocalTransform();
+    if (!size_.IsEmpty()) {
+      transform.Scale(size_.width(), size_.height());
+    }
 
-  if (parent_) {
-    inheritable.ConcatTransform(parent_->inheritable_transform());
+    // Compute an inheritable transformation that can be applied to this
+    // element, and it's children, if applicable.
+    gfx::Transform inheritable = LocalTransform();
+
+    if (parent_) {
+      inheritable.ConcatTransform(parent_->inheritable_transform());
+    }
+
+    transform.ConcatTransform(inheritable);
+    set_world_space_transform(transform);
+    set_inheritable_transform(inheritable);
+    changed = true;
   }
 
-  transform.ConcatTransform(inheritable);
-  set_world_space_transform(transform);
-  set_inheritable_transform(inheritable);
   set_update_phase(kUpdatedWorldSpaceTransform);
-
   for (auto& child : children_) {
-    child->UpdateWorldSpaceTransformRecursive();
+    child->UpdateWorldSpaceTransformRecursive(changed);
   }
 
   OnUpdatedWorldSpaceTransform();
 }
 
 gfx::Transform UiElement::LocalTransform() const {
-  return layout_offset_.Apply() * transform_operations_.Apply();
+  return local_transform_;
 }
 
 gfx::Transform UiElement::GetTargetLocalTransform() const {
@@ -840,4 +884,9 @@ const Sounds& UiElement::GetSounds() const {
   return sounds_;
 }
 
+bool UiElement::ShouldUpdateWorldSpaceTransform(
+    bool parent_transform_changed) const {
+  return parent_transform_changed || world_space_transform_dirty_;
+}
+
 }  // namespace vr

chrome/browser/vr/elements/ui_element.h

@@ -337,6 +337,7 @@ class UiElement : public cc::AnimationTarget {
   const gfx::Transform& world_space_transform() const;
   void set_world_space_transform(const gfx::Transform& transform) {
     world_space_transform_ = transform;
+    world_space_transform_dirty_ = false;
   }
 
   gfx::Transform ComputeTargetWorldSpaceTransform() const;
@@ -413,7 +414,7 @@ class UiElement : public cc::AnimationTarget {
   virtual gfx::Transform GetTargetLocalTransform() const;
 
   void UpdateComputedOpacity();
-  void UpdateWorldSpaceTransformRecursive();
+  void UpdateWorldSpaceTransformRecursive(bool parent_changed);
 
   std::vector<std::unique_ptr<UiElement>>& children() { return children_; }
   const std::vector<std::unique_ptr<UiElement>>& children() const {
@@ -492,6 +493,13 @@ class UiElement : public cc::AnimationTarget {
 
   virtual const Sounds& GetSounds() const;
 
+  virtual bool ShouldUpdateWorldSpaceTransform(
+      bool parent_transform_changed) const;
+
+  void set_world_space_transform_dirty() {
+    world_space_transform_dirty_ = true;
+  }
+
   EventHandlers event_handlers_;
 
  private:
@@ -601,12 +609,16 @@ class UiElement : public cc::AnimationTarget {
   // the translation, but leave the rotation and scale in tact).
   cc::TransformOperations transform_operations_;
 
+  // This is a cached version of the local transform.
+  gfx::Transform local_transform_;
+
   // This is set by the parent and is combined into LocalTransform()
   cc::TransformOperations layout_offset_;
 
   // This is the combined, local to world transform. It includes
   // |inheritable_transform_|, |transform_|, and anchoring adjustments.
   gfx::Transform world_space_transform_;
+  bool world_space_transform_dirty_ = false;
 
   UiElement* parent_ = nullptr;
   std::vector<std::unique_ptr<UiElement>> children_;

chrome/browser/vr/elements/ui_element_unittest.cc

@@ -115,7 +115,7 @@ TEST(UiElement, IgnoringAsymmetricPadding) {
   a->AddChild(std::move(b));
   a->DoLayOutChildren();
 
-  a->UpdateWorldSpaceTransformRecursive();
+  a->UpdateWorldSpaceTransformRecursive(false);
 
   gfx::Point3F p;
   a->world_space_transform().TransformPoint(&p);

chrome/browser/vr/ui_scene.cc

@@ -128,7 +128,8 @@ bool UiScene::OnBeginFrame(const base::TimeTicks& current_time,
 
     // Now that we have finalized our local values, we can safely update our
     // final, baked transform.
-    root_element_->UpdateWorldSpaceTransformRecursive();
+    const bool parent_transform_changed = false;
+    root_element_->UpdateWorldSpaceTransformRecursive(parent_transform_changed);
   }
 
   return scene_dirty;