Pass MotionEvent tilt angles to Blink on Android.

content/browser/renderer_host/input/motion_event_web.cc

Index: content/browser/renderer_host/input/motion_event_web.cc
diff --git a/content/browser/renderer_host/input/motion_event_web.cc b/content/browser/renderer_host/input/motion_event_web.cc
index ddc30372cdad50a5373227cd1bd12117db61d99e..f5866de78a23077b025c262850b61b6a46559307 100644
--- a/content/browser/renderer_host/input/motion_event_web.cc
+++ b/content/browser/renderer_host/input/motion_event_web.cc
@@ -130,26 +130,58 @@ float MotionEventWeb::GetTouchMinor(size_t pointer_index) const {
 float MotionEventWeb::GetOrientation(size_t pointer_index) const {
   DCHECK_LT(pointer_index, GetPointerCount());
 
-  float rotation_angle_rad = event_.touches[pointer_index].rotationAngle
+  float orientation_rad = event_.touches[pointer_index].rotationAngle
       * M_PI / 180.f;
-  DCHECK(0 <= rotation_angle_rad && rotation_angle_rad <= M_PI_2)
+  DCHECK(0 <= orientation_rad && orientation_rad <= M_PI_2)
       << "Unexpected touch rotation angle";
 
-  if (event_.touches[pointer_index].radiusX
-      > event_.touches[pointer_index].radiusY) {
+  if (GetToolType(pointer_index) == TOOL_TYPE_STYLUS) {
+    const WebPointerProperties& pointer = event_.touches[pointer_index];
+
+    if (pointer.tiltY < 0) {

[tdresser, 2015/11/02 14:44:07]

I think this would be easier to read if you explicitly check all four quadrants.

i.e.

if (pointer.tiltY < 0 && pointer.tiltX < 0)
  ...
else if(pointer.tiltY < 0 && pointer.tiltX > 0)
  ...
else if(pointer.tiltY > 0 && pointer.tiltX < 0)
  ...
else
  ...

[e_hakkinen, 2015/11/02 16:27:16]

Yes, especially because the grouping was not actually entirely correct.
The first condition should be
  if (pointer.tiltY <= 0 && pointer.tiltX < 0)
instead of
  if (pointer.tiltY < 0 && pointer.tiltX < 0)
thus this code did not handle correctly the case when a stylus was tilted
straight to the left.

I flattened the nested if blocks and amended the unit test to check that special
case, too.
Done.

+      if (pointer.tiltX < 0)
+        orientation_rad += static_cast<float>(M_PI_2);
+      else
+        orientation_rad -= static_cast<float>(M_PI);
+    } else {
+      if (pointer.tiltX > 0)
+        orientation_rad -= static_cast<float>(M_PI_2);
+    }
+  } else if (event_.touches[pointer_index].radiusX
+             > event_.touches[pointer_index].radiusY) {
     // The case radiusX == radiusY is omitted from here on purpose: for circles,
     // we want to pass the angle (which could be any value in such cases but
     // always seem to be set to zero) unchanged.

[tdresser, 2015/11/02 14:44:07]

While you're editing this, can you change:
"always seem" -> "always seems"?

[e_hakkinen, 2015/11/02 16:27:16]

Done.

-    rotation_angle_rad -= (float) M_PI_2;
+    orientation_rad -= static_cast<float>(M_PI_2);
   }
 
-  return rotation_angle_rad;
+  return orientation_rad;
 }
 
 float MotionEventWeb::GetPressure(size_t pointer_index) const {
   return 0.f;
 }
 
+float MotionEventWeb::GetTilt(size_t pointer_index) const {
+  DCHECK_LT(pointer_index, GetPointerCount());
+
+  if (GetToolType(pointer_index) != TOOL_TYPE_STYLUS)
+    return 0.f;
+
+  const WebPointerProperties& pointer = event_.touches[pointer_index];
+
+  float tilt_x_r = sin(pointer.tiltX * M_PI / 180.f);
+  float tilt_x_z = cos(pointer.tiltX * M_PI / 180.f);
+  float tilt_y_r = sin(pointer.tiltY * M_PI / 180.f);
+  float tilt_y_z = cos(pointer.tiltY * M_PI / 180.f);
+  float r_x = tilt_x_r * tilt_y_z;
+  float r_y = tilt_y_r * tilt_x_z;
+  float r = sqrt(r_x * r_x + r_y * r_y);
+  float z = tilt_x_z * tilt_y_z;
+
+  return atan2(r, z);
+}
+
 base::TimeTicks MotionEventWeb::GetEventTime() const {
   return base::TimeTicks() +
          base::TimeDelta::FromMicroseconds(event_.timeStampSeconds *