Mozart: Implement hit testing.

services/gfx/compositor/graph/node_def.cc

Index: services/gfx/compositor/graph/node_def.cc
diff --git a/services/gfx/compositor/graph/node_def.cc b/services/gfx/compositor/graph/node_def.cc
index 6a1dfc9a974083244d8bf59ee8bcbe6a2a86f066..6092bab1c79677760dafc30201125752b4960b90 100644
--- a/services/gfx/compositor/graph/node_def.cc
+++ b/services/gfx/compositor/graph/node_def.cc
@@ -15,7 +15,9 @@
 #include "services/gfx/compositor/render/render_image.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkColor.h"
+#include "third_party/skia/include/core/SkMatrix.h"
 #include "third_party/skia/include/core/SkPaint.h"
+#include "third_party/skia/include/core/SkPoint.h"
 #include "third_party/skia/include/core/SkRect.h"
 
 namespace compositor {
@@ -29,16 +31,23 @@ void SetPaintForBlend(SkPaint* paint, mojo::gfx::composition::Blend* blend) {
   if (blend)
     paint->setAlpha(blend->alpha);
 }
+
+bool Contains(const SkRect& bounds, const SkPoint& point) {
+  return point.x() >= bounds.left() && point.x() < bounds.right() &&
+         point.y() >= bounds.top() && point.y() < bounds.bottom();
+}
 }  // namespace
 
 NodeDef::NodeDef(uint32_t node_id,
                  mojo::TransformPtr content_transform,
                  mojo::RectPtr content_clip,
+                 mojo::gfx::composition::HitTestBehaviorPtr hit_test_behavior,
                  Combinator combinator,
                  const std::vector<uint32_t>& child_node_ids)
     : node_id_(node_id),
       content_transform_(content_transform.Pass()),
       content_clip_(content_clip.Pass()),
+      hit_test_behavior_(hit_test_behavior.Pass()),
       combinator_(combinator),
       child_node_ids_(child_node_ids) {}
 
@@ -222,16 +231,105 @@ void NodeDef::RecordPictureInner(const SceneContent* content,
       });
 }
 
-RectNodeDef::RectNodeDef(uint32_t node_id,
-                         mojo::TransformPtr content_transform,
-                         mojo::RectPtr content_clip,
-                         Combinator combinator,
-                         const std::vector<uint32_t>& child_node_ids,
-                         const mojo::Rect& content_rect,
-                         const mojo::gfx::composition::Color& color)
+void NodeDef::HitTest(const SceneContent* content,
+                      const Snapshot* snapshot,
+                      const SkPoint& global_point,
+                      const SkMatrix& parent_transform,
+                      bool* opaque,
+                      mojo::Array<mojo::gfx::composition::HitPtr>* hits) const {
+  DCHECK(content);
+  DCHECK(snapshot);
+  DCHECK(opaque);
+  DCHECK(hits);
+
+  SkMatrix node_transform = parent_transform;
+  if (content_transform_)
+    node_transform.postConcat(content_transform_.To<SkMatrix>());

[abarth, 2016/03/09 04:02:48]

I think you want to do this work in 4x4 matrices.

[jeffbrown, 2016/03/09 20:32:11]

You're probably right.  Noted for later since this affects the drawing pipeline
too.

+  if (content_clip_) {
+    SkRect global_clip_rect;
+    node_transform.mapRect(&global_clip_rect, content_clip_->To<SkRect>());

[abarth, 2016/03/09 04:02:48]

This isn't very efficient because you're doing a matrix multiplication at every
level of recursion.  One pattern that works reasonably well for hit testing is
to pass the point you're hit testing in the parent's coordinate system.  You
always have that because you needed to test against the parent.  The child can
either re-use that point or can adjust it by the content_transform_.

[jeffbrown, 2016/03/09 20:32:11]

I previously wrote the code that way.  The trade-off is that in order to
calculate that point, you need to apply the inverse matrix.  I figured 4
matrix*vector multiplications only at nodes which have clips was better than 1
matrix inversion at every node.

In retrospect, this isn't so bad if I just cache the inverse matrix.

+    if (!Contains(global_clip_rect, global_point))
+      return;
+  }
+
+  if (!hit_test_behavior_ || !hit_test_behavior_->prune)
+    HitTestInner(content, snapshot, global_point, node_transform, opaque, hits);
+
+  if (!hit_test_behavior_ ||
+      hit_test_behavior_->visibility ==
+          mojo::gfx::composition::HitTestBehavior::Visibility::INVISIBLE)
+    return;
+
+  if (hit_test_behavior_->hit_rect) {
+    SkRect global_hit_rect;
+    node_transform.mapRect(&global_hit_rect,
+                           hit_test_behavior_->hit_rect->To<SkRect>());
+    if (!Contains(global_hit_rect, global_point))
+      return;
+  }
+
+  if (hit_test_behavior_->visibility ==
+      mojo::gfx::composition::HitTestBehavior::Visibility::OPAQUE)
+    *opaque = true;
+
+  SkMatrix inverse_node_transform;
+  if (!node_transform.invert(&inverse_node_transform)) {
+    // Matrix is singular!
+    // Return [0,0,0][0,0,0][0,0,1] (all zeroes except last component).
+    // This causes all points to be mapped to (0,0) when transformed.
+    inverse_node_transform.setScale(0.f, 0.f);
+  }
+
+  auto hit = mojo::gfx::composition::Hit::New();
+  hit->set_node(mojo::gfx::composition::NodeHit::New());
+  hit->get_node()->node_id = node_id_;
+  hit->get_node()->transform =
+      mojo::ConvertTo<mojo::TransformPtr>(inverse_node_transform);
+  hits->push_back(hit.Pass());
+}
+
+void NodeDef::HitTestInner(

[abarth, 2016/03/09 04:02:48]

s/HitTestInner/HitTestChildren/ ?

[jeffbrown, 2016/03/09 20:32:11]

Strictly speaking it's not just children since referenced scenes are handled
here too.  Agree that it's confusing.

+    const SceneContent* content,
+    const Snapshot* snapshot,
+    const SkPoint& global_point,
+    const SkMatrix& node_transform,
+    bool* opaque,
+    mojo::Array<mojo::gfx::composition::HitPtr>* hits) const {
+  DCHECK(content);
+  DCHECK(snapshot);
+  DCHECK(opaque);
+  DCHECK(hits);
+
+  // TODO(jeffbrown): Implement a more efficient way to traverse children in
+  // reverse order.
+  std::vector<const NodeDef*> children;
+  TraverseSnapshottedChildren(
+      content, snapshot, [this, &children](const NodeDef* child_node) -> bool {
+        children.push_back(child_node);
+        return true;
+      });
+
+  for (auto it = children.crbegin(); it != children.crend(); ++it) {
+    (*it)->HitTest(content, snapshot, global_point, node_transform, opaque,
+                   hits);
+    if (*opaque)

[abarth, 2016/03/09 04:02:48]

In other systems, we've passed this value through the return value rather than
an out-param, but either works.

[jeffbrown, 2016/03/09 20:32:11]

SceneContent::HitTest returns a SceneHitPtr as its result so it ended up with an
opaque out-param, and that ultimately determined the shape of the parameter list
deeper in the recursion.

Since the opaque flag governs more of the flow control than that thing, I think
I'll flip it around.

+      break;
+  }
+}
+
+RectNodeDef::RectNodeDef(
+    uint32_t node_id,
+    mojo::TransformPtr content_transform,
+    mojo::RectPtr content_clip,
+    mojo::gfx::composition::HitTestBehaviorPtr hit_test_behavior,
+    Combinator combinator,
+    const std::vector<uint32_t>& child_node_ids,
+    const mojo::Rect& content_rect,
+    const mojo::gfx::composition::Color& color)
     : NodeDef(node_id,
               content_transform.Pass(),
               content_clip.Pass(),
+              hit_test_behavior.Pass(),
               combinator,
               child_node_ids),
       content_rect_(content_rect),
@@ -253,18 +351,21 @@ void RectNodeDef::RecordPictureInner(const SceneContent* content,
   NodeDef::RecordPictureInner(content, snapshot, canvas);
 }
 
-ImageNodeDef::ImageNodeDef(uint32_t node_id,
-                           mojo::TransformPtr content_transform,
-                           mojo::RectPtr content_clip,
-                           Combinator combinator,
-                           const std::vector<uint32_t>& child_node_ids,
-                           const mojo::Rect& content_rect,
-                           mojo::RectPtr image_rect,
-                           uint32 image_resource_id,
-                           mojo::gfx::composition::BlendPtr blend)
+ImageNodeDef::ImageNodeDef(
+    uint32_t node_id,
+    mojo::TransformPtr content_transform,
+    mojo::RectPtr content_clip,
+    mojo::gfx::composition::HitTestBehaviorPtr hit_test_behavior,
+    Combinator combinator,
+    const std::vector<uint32_t>& child_node_ids,
+    const mojo::Rect& content_rect,
+    mojo::RectPtr image_rect,
+    uint32 image_resource_id,
+    mojo::gfx::composition::BlendPtr blend)
     : NodeDef(node_id,
               content_transform.Pass(),
               content_clip.Pass(),
+              hit_test_behavior.Pass(),
               combinator,
               child_node_ids),
       content_rect_(content_rect),
@@ -306,16 +407,19 @@ void ImageNodeDef::RecordPictureInner(const SceneContent* content,
   NodeDef::RecordPictureInner(content, snapshot, canvas);
 }
 
-SceneNodeDef::SceneNodeDef(uint32_t node_id,
-                           mojo::TransformPtr content_transform,
-                           mojo::RectPtr content_clip,
-                           Combinator combinator,
-                           const std::vector<uint32_t>& child_node_ids,
-                           uint32_t scene_resource_id,
-                           uint32_t scene_version)
+SceneNodeDef::SceneNodeDef(
+    uint32_t node_id,
+    mojo::TransformPtr content_transform,
+    mojo::RectPtr content_clip,
+    mojo::gfx::composition::HitTestBehaviorPtr hit_test_behavior,
+    Combinator combinator,
+    const std::vector<uint32_t>& child_node_ids,
+    uint32_t scene_resource_id,
+    uint32_t scene_version)
     : NodeDef(node_id,
               content_transform.Pass(),
               content_clip.Pass(),
+              hit_test_behavior.Pass(),
               combinator,
               child_node_ids),
       scene_resource_id_(scene_resource_id),
@@ -368,24 +472,51 @@ void SceneNodeDef::RecordPictureInner(const SceneContent* content,
   const SceneContent* resolved_content =
       snapshot->GetResolvedSceneContent(this);
   DCHECK(resolved_content);
-
-  const NodeDef* root_node = resolved_content->GetRootNodeIfExists();
-  DCHECK(root_node);  // must have a root otherwise would have been blocked
-  root_node->RecordPicture(resolved_content, snapshot, canvas);
+  resolved_content->RecordPicture(snapshot, canvas);
 
   NodeDef::RecordPictureInner(content, snapshot, canvas);
 }
 
-LayerNodeDef::LayerNodeDef(uint32_t node_id,
-                           mojo::TransformPtr content_transform,
-                           mojo::RectPtr content_clip,
-                           Combinator combinator,
-                           const std::vector<uint32_t>& child_node_ids,
-                           const mojo::Size& size,
-                           mojo::gfx::composition::BlendPtr blend)
+void SceneNodeDef::HitTestInner(
+    const SceneContent* content,
+    const Snapshot* snapshot,
+    const SkPoint& global_point,
+    const SkMatrix& node_transform,
+    bool* opaque,
+    mojo::Array<mojo::gfx::composition::HitPtr>* hits) const {
+  DCHECK(content);
+  DCHECK(snapshot);
+  DCHECK(opaque);
+  DCHECK(hits);
+
+  NodeDef::HitTestInner(content, snapshot, global_point, node_transform, opaque,
+                        hits);

[abarth, 2016/03/09 04:02:48]

Do we need to test opaque after calling this function?

[jeffbrown, 2016/03/09 20:32:11]

Initially I didn't think so since I was imagining the reference scene as being
part of its parent node and should therefore get a shot at the hit test even if
opaque children were hit.  But on reflection that might be confusion to folks so
let's change it.

+
+  const SceneContent* resolved_content =
+      snapshot->GetResolvedSceneContent(this);
+  DCHECK(resolved_content);
+  mojo::gfx::composition::SceneHitPtr scene_hit =
+      resolved_content->HitTest(snapshot, global_point, node_transform, opaque);
+  if (scene_hit) {
+    auto hit = mojo::gfx::composition::Hit::New();
+    hit->set_scene(scene_hit.Pass());
+    hits->push_back(hit.Pass());
+  }
+}
+
+LayerNodeDef::LayerNodeDef(
+    uint32_t node_id,
+    mojo::TransformPtr content_transform,
+    mojo::RectPtr content_clip,
+    mojo::gfx::composition::HitTestBehaviorPtr hit_test_behavior,
+    Combinator combinator,
+    const std::vector<uint32_t>& child_node_ids,
+    const mojo::Size& size,
+    mojo::gfx::composition::BlendPtr blend)
     : NodeDef(node_id,
               content_transform.Pass(),
               content_clip.Pass(),
+              hit_test_behavior.Pass(),
               combinator,
               child_node_ids),
       size_(size),