Implement HitTestAggregator

services/viz/hit_test/public/interfaces/hit_test_data.mojom

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module viz.hit_test.mojom;
+
+import "cc/ipc/surface_id.mojom";
+import "ui/gfx/geometry/mojo/geometry.mojom";
+import "ui/gfx/mojo/transform.mojom";
+
+// Region maps to this surface ( me ).
+const uint32 kHitTestMine = 0x01;
+
+// Region ignored for hit testing ( transparent backgrounds & hover:none ).
+const uint32 kHitTestIgnore = 0x02;
+
+// Region maps to child surface ( OOPIF ).
+const uint32 kHitTestChildSurface = 0x04;
+
+// Irregular boundary - send HitTestRequest to resolve.
+const uint32 kHitTestAsk = 0x08;
+
+// No touch event handler exists - no need to send touch events.
+const uint32 kHitTestNoTouchEventHandler = 0x10;
+
+struct HitTestRegion {
+
+    // Flags to indicate the type of HitTestRegion.
+    uint32 flags;
+
+    // SurfaceId is required when flags = kHitTestChildSurface.
+    cc.mojom.SurfaceId surface_id;
+
+    // The rect of the region in the coordinate space of the embedder.
+    gfx.mojom.Rect rect;
+
+    // The transform applied to the child region.
+    gfx.mojom.Transform transform;
+};
+
+struct HitTestData {
+
+  // SurfaceId corresponding to this HitTestData.

[rjkroege, 2017/06/27 00:00:07]

I've observed before: all of this info could just be in the 0-th HitTestRegion.
I'm not sure if that's a good idea or not. But it has (at least to me) a
pleasant regularity.

[gklassen, 2017/06/27 21:46:33]

I agree and my initial attempt was to build it this way - but the code that
builds the tree got a little too strange for my comfort because it had to
inspect the 0-th element and handle it differently.  Writing it this way seemed
to keep the implementation cleaner because all regions are handled the same way
and it makes requirement for flags, bounds and transform in the hit_test_data
structure explicit and required. 

+  cc.mojom.SurfaceId surface_id;
+
+  // Flags indicate how to handle events that match no sub-regions.
+  // kHitTestMine routes un-matched events to this surface ( opaque ).
+  // kHitTestIgnore keeps previous match in the parent ( transparent ).
+  uint32 flags;
+
+  // The bounds of the surface.
+  gfx.mojom.Rect bounds;
+
+  // The transform that applies to all regions in this surface.
+  gfx.mojom.Transform transform;
+
+  // The list of sub-regions in front to back order.
+  //TODO(gklassen): invert order if its easier to write them back to front.
+  array<HitTestRegion> regions;
+};