Eraser tool type plumbing from ui/events to web events and PPAPI.

ppapi/api/ppb_input_event.idl

 /* Copyright (c) 2012 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.
  */
 
 /**
  * This file defines the Input Event interfaces.
  */
 
 label Chrome {
   M13 = 1.0,
   M14 = 1.1,
-  M34 = 1.2
+  M34 = 1.2,
+  M54 = 1.3

[bbudge, 2016/08/30 22:05:54]

This doesn't actually version the API

I'm going to reverse myself on this. To properly version this API would be
difficult, and the chance of this change breaking an existing app seems remote
(basically an app would have to be depending on these modifier bits being zero.)

A plugin that knows about these modifiers should run fine on older versions of
Chrome - it would just receive unmodified mouse events, which it should be able
to handle in any case. On versions of Chrome that do support these bits, the app
would be able to detect that and handle those modified events differently.

Since we don't really support versioning enum values (the code generator just
ignores those) you'd have to version the PPP_InputEvent interface, which is how
plugins receive events. Versioning PPP interfaces is more difficult. You would
have to modify a lot of Pepper code and check for API versions in the Pepper
proxy.

So this is fine as it is. It would probably be a good idea to annotate the new
values below with the version. See this CL which added a flag to the PPB_FileIO
API (which was technically a breaking change to a Stable API):

https://chromiumcodereview.appspot.com/16765005

[denniskempin, 2016/09/01 16:56:21]

There is one problem that I could see: 

Older versions of chrome do not filter the modifier flags. ISPEN and ISERASER
will be mapped to IsTouchAccessibility or IsComposing of
WebInputEvent::Modifiers. 

So running an app that uses the PEN/ERASER flags might break in weird ways in
older versions of chrome. Can the app query this input API version and disable
checking for the eraser flag? I have never used PPAPI myself. 

I will add the version flags to the enum values below. 

 };
 
 /**
  * This enumeration contains the types of input events.
  */
 [assert_size(4)]
 enum PP_InputEvent_Type {
   PP_INPUTEVENT_TYPE_UNDEFINED = -1,
 
   /**
@@ skipping 168 matching lines @@
   PP_INPUTEVENT_MODIFIER_ALTKEY           = 1 << 2,
   PP_INPUTEVENT_MODIFIER_METAKEY          = 1 << 3,
   PP_INPUTEVENT_MODIFIER_ISKEYPAD         = 1 << 4,
   PP_INPUTEVENT_MODIFIER_ISAUTOREPEAT     = 1 << 5,
   PP_INPUTEVENT_MODIFIER_LEFTBUTTONDOWN   = 1 << 6,
   PP_INPUTEVENT_MODIFIER_MIDDLEBUTTONDOWN = 1 << 7,
   PP_INPUTEVENT_MODIFIER_RIGHTBUTTONDOWN  = 1 << 8,
   PP_INPUTEVENT_MODIFIER_CAPSLOCKKEY      = 1 << 9,
   PP_INPUTEVENT_MODIFIER_NUMLOCKKEY       = 1 << 10,
   PP_INPUTEVENT_MODIFIER_ISLEFT           = 1 << 11,
-  PP_INPUTEVENT_MODIFIER_ISRIGHT          = 1 << 12
+  PP_INPUTEVENT_MODIFIER_ISRIGHT          = 1 << 12,
+  PP_INPUTEVENT_MODIFIER_ISPEN            = 1 << 13,
+  PP_INPUTEVENT_MODIFIER_ISERASER         = 1 << 14

[bbudge, 2016/08/30 22:05:54]

Annotate these both with [version=1.3] even though it's essentially a no-op.

[denniskempin, 2016/09/01 16:56:21]

Acknowledged.

 };
 
 /**
  * This enumeration contains constants representing each mouse button. To get
  * the mouse button for a mouse down or up event, use GetMouseButton on
  * PPB_InputEvent.
  */
 [assert_size(4)]
 enum PP_InputEvent_MouseButton {
   PP_INPUTEVENT_MOUSEBUTTON_NONE   = -1,
@@ skipping 865 matching lines @@
    * event.
    *
    * @param[out] start The start position of the current selection.
    *
    * @param[out] end The end position of the current selection.
    */
   void GetSelection([in] PP_Resource ime_event,
                     [out] uint32_t start,
                     [out] uint32_t end);
 };