Make a pen in eraser mode visible thru PointerEvent.buttons

third_party/WebKit/Source/core/events/PointerEventFactory.cpp

Index: third_party/WebKit/Source/core/events/PointerEventFactory.cpp
diff --git a/third_party/WebKit/Source/core/events/PointerEventFactory.cpp b/third_party/WebKit/Source/core/events/PointerEventFactory.cpp
index 4ca7e61e874a846d55d263cfcaad3cb2af24b636..123369f612b68341f789a8fa11292231c029d95a 100644
--- a/third_party/WebKit/Source/core/events/PointerEventFactory.cpp
+++ b/third_party/WebKit/Source/core/events/PointerEventFactory.cpp
@@ -22,6 +22,7 @@ const char* pointerTypeNameForWebPointPointerType(WebPointerProperties::PointerT
         return "touch";
     case WebPointerProperties::PointerType::Pen:
     case WebPointerProperties::PointerType::Eraser:
+        // TODO(mustaq): Fix when the spec starts supporting hovering erasers.
         return "pen";
     case WebPointerProperties::PointerType::Mouse:
         return "mouse";
@@ -78,8 +79,10 @@ const int PointerEventFactory::s_mouseId = 1;
 
 float getPointerEventPressure(float force, int buttons)
 {
-    if (std::isnan(force))
-        return buttons ? 0.5 : 0;
+    if (std::isnan(force)) {
+        // TODO(mustaq): Fix when the spec starts supporting hovering erasers.
+        return (buttons & ~static_cast<unsigned>(MouseEvent::Buttons::Eraser)) ? 0.5 : 0;
+    }
     return force;
 }
 
@@ -90,7 +93,13 @@ void PointerEventFactory::setIdTypeButtons(PointerEventInit& pointerEventInit,
     const IncomingId incomingId(pointerType, pointerProperties.id);
     int pointerId = addIdAndActiveButtons(incomingId, buttons != 0);
 
+    // Tweak the |buttons| to reflect pen eraser mode only if the pen is in
+    // active buttons state w/o even considering the eraser button.
+    // TODO(mustaq): Fix when the spec starts supporting hovering erasers.
+    if (pointerType == WebPointerProperties::PointerType::Eraser && buttons != 0)

[Navid Zolghadr, 2016/08/31 20:01:16]

I wonder if we can just do this when pointerType is Eraser regardless of the
fact that any other button is pressed or not. That would make buttons=32 as soon
as an eraser comes into the range of digitizer as oppose to the current model
which hides the fact that the eraser is near the screen and makes it similar to
pen near the screen case but as soon as the eraser touches the screen it shows
button=33.

[mustaq, 2016/08/31 20:29:37]

I don't like this for two reasons:

[A] That would mean that a flipped pen should either:
- fire a "pointerdown" at the moment if comes within the digitizer range while
hovering, or
- never fire a "pointerdown",
because it will never switch between active/inactive buttons states /after/
being in active state
https://w3c.github.io/pointerevents/#the-pointerdown-event.
Same applies for "pointerup".

[B] From another perspective of the spec, the eraser mode can only switch
between two states (inactive, and active+activeButton). Why should it be so
different from the pen mode that can switch between:
  inactive <-> active <-> activeButton
states?

I think conceptually "pointerdown" and "pointerup" marks the
active<->activeButton state transitions in the spec, and this is very intuitive.

+        buttons |= static_cast<unsigned>(MouseEvent::Buttons::Eraser);
     pointerEventInit.setButtons(buttons);
+
     pointerEventInit.setPointerId(pointerId);
     pointerEventInit.setPointerType(pointerTypeNameForWebPointPointerType(pointerType));
     pointerEventInit.setIsPrimary(isPrimary(pointerId));