Ozone keyboard layout

ui/events/ozone/layout/keyboard_layout_engine.h

+// Copyright 2014 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.
+
+#ifndef UI_OZONE_PUBLIC_KEYBOARD_LAYOUT_ENGINE_H_
+#define UI_OZONE_PUBLIC_KEYBOARD_LAYOUT_ENGINE_H_
+
+#include <string>
+
+#include "base/strings/string16.h"
+#include "ui/events/keycodes/keyboard_codes.h"
+#include "ui/events/ozone/layout/events_ozone_layout_export.h"
+
+namespace ui {
+
+enum class DomCode;
+enum class DomKey;
+
+// A KeyboardLayoutEngine provides a platform-independent interface to
+// key mapping. Key mapping provides a meaning (DomKey and character,
+// and optionally Windows key code) for a physical key press (DomCode
+// and modifier flags).
+//
+// The interface must support platforms that only provide a single opaque
+// system layout, so there is no standalone 'KeyboardLayout' object.
+class EVENTS_OZONE_LAYOUT_EXPORT KeyboardLayoutEngine {
+ public:
+  KeyboardLayoutEngine() {}
+  virtual ~KeyboardLayoutEngine() {}
+
+  // Returns true if it is possible to change the current layout.
+  virtual bool CanSetCurrentLayout() const = 0;
+
+  // Sets the current layout; returns true on success.
+  virtual bool SetCurrentLayoutByName(const std::string& layout_name) = 0;

[Wez, 2014/12/09 07:00:33]

What's the format of the layout name? Or is that platform specific?

[kpschoedel, 2014/12/09 19:58:44]

This is currently a drop-in replacement for
ImeKeyboard::SetCurrentKeyboardLayoutByName(), which means the argument is (1)
not explicitly defined, and (2) in practice an XKB RMLVO name. The interface
here currently open for revision with the IME folks.

[Wez, 2014/12/12 20:04:17]

OK, SGTM; consider referencing the corresponding bug for that in the comment.

[kpschoedel, 2014/12/12 21:20:39]

Done.

+
+  // Returns true if the current layout makes use of the ISO Level 5 Shift key.
+  virtual bool UsesISOLevel5Shift() const = 0;

[Wez, 2014/12/09 07:00:33]

Do you mean Level 5 shift, or Level 3?

[kpschoedel, 2014/12/09 19:58:44]

Level 5. This again is a drop-in for ImeKeyboard::IsISOLevel5ShiftAvailable(),
slightly renamed because I could never remember whether 'Available' means the
layout uses it or doesn't use it.

+
+  // Returns true if the current layout makes use of the AltGr
+  // (ISO Level 3 Shift) key.
+  virtual bool UsesAltGr() const = 0;
+
+  // Provides the meaning of a physical key.
+  //
+  // The caller must supply valid addresses for all the output parameters;
+  // the function must not use their initial values.
+  //
+  // Returns true if it can determine the meaning of the (dom_code, flags)
+  // values, OR if it can determine that they have no meaning in the current
+  // layout (e.g. the key is unbound). In the latter case, the function sets
+  // *dom_key to UNIDENTIFIED, *character to 0, and *key_code to VKEY_UNKNOWN.

[Wez, 2014/12/09 07:00:33]

Do all implementations have to set all of the fields, or can they opt to e.g.
not set the KeyboardCode?

[kpschoedel, 2014/12/09 19:58:44]

This was up in the air for a while, but I've settled on requiring it, as
determining it can require multiple calls to the underlying layout mechanism (as
in ui/events/keycodes/keyboard_code_conversion_x.cc) and I think it's better
done here than in the caller(s). A likely near-term plan is to factor out the
XkbKeyboardLayoutEngine code for this.

[Wez, 2014/12/12 20:04:17]

OK, sounds reasonable.

+  //
+  // Returns false if it cannot determine the meaning (and cannot determine
+  // that there is none); in this case it does not set any of the output
+  // parameters.
+  virtual bool Lookup(DomCode dom_code,
+                      int flags,

[Wez, 2014/12/09 07:00:33]

What are the contents of |flags|?

[kpschoedel, 2014/12/09 19:58:44]

ui::EventFlags, which is an unscoped enum. Most existing uses of it are typed
|int|.

[Wez, 2014/12/12 20:04:17]

Suggest clarifying that it's ui::EventFlags in the comment.

[kpschoedel, 2014/12/12 21:20:39]

Done.

+                      DomKey* dom_key,
+                      base::char16* character,

[Wez, 2014/12/09 07:00:33]

There isn't a 1:1 correspondence between keys and characters, e.g. due to dead
keys, IMEs, etc. Have you considered breaking apart the Code->Key conversion
from the sequence-of-Key->character conversion engines?

[kpschoedel, 2014/12/09 19:58:44]

Not in the short term; it's currently wrapped up with IME. For now this is just
a slight abstraction of core X11 XKB.

+                      KeyboardCode* key_code) const = 0;
+};
+
+}  // namespace ui
+
+#endif  // UI_OZONE_PUBLIC_KEYBOARD_LAYOUT_ENGINE_H_