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..30f141bebd71b4022fc17c7e995f4972b9e82588 100644
--- a/content/browser/renderer_host/input/motion_event_web.cc
+++ b/content/browser/renderer_host/input/motion_event_web.cc
@@ -130,26 +130,62 @@ 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 && pointer.tiltX < 0) {
+      // Stylus is tilted to the left away from the user or straight
+      // to the left thus the orientation should be within [pi/2,pi).
+      orientation_rad += static_cast<float>(M_PI_2);
+    } else if (pointer.tiltY < 0 && pointer.tiltX >= 0) {
+      // Stylus is tilted to the right away from the user or straight away
+      // from the user thus the orientation should be within [-pi,-pi/2).
+      orientation_rad -= static_cast<float>(M_PI);
+    } else if (pointer.tiltY >= 0 && pointer.tiltX > 0) {
+      // Stylus is tilted to the right towards the user or straight
+      // to the right thus the orientation should be within [-pi/2,0).
+      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.
-    rotation_angle_rad -= (float) M_PI_2;
+    // always seems to be set to zero) unchanged.
+    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 *