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diff --git a/tools/viewer/sk_app/CommandSet.h b/tools/viewer/sk_app/CommandSet.h
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+++ b/tools/viewer/sk_app/CommandSet.h
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+/*
+* Copyright 2016 Google Inc.
+*
+* Use of this source code is governed by a BSD-style license that can be
+* found in the LICENSE file.
+*/
+
+#ifndef CommandSet_DEFINED
+#define CommandSet_DEFINED
+
+#include "SkString.h"
+#include "Window.h"
+
+#include <functional>
+
+class SkCanvas;
+
+namespace sk_app {
+
+/**
+ * Helper class used by applications that want to hook keypresses to trigger events.
+ *
+ * An app can simply store an instance of CommandSet and then use it as follows:
+ * 1) Attach to the Window at initialization time. This registers key handlers on the window.
+ * 2) Register commands to be executed for characters or keys. Each command needs a Group and a
+ *    description (both just strings). Commands attached to Keys (rather than characters) also need
+ *    a displayable name for the Key. Finally, a function to execute when the key or character is
+ *    pressed must be supplied. The easiest option to is pass in a lambda that captures [this]
+ *    (your application object), and performs whatever action is desired.
+ * 3) At the end of your onPaint, call drawHelp, and pass in the application's canvas.
+
+ * The CommandSet always binds 'h' to cycle through two different help screens. The first shows
+ * all commands, organized by Group (with headings for each Group). The second shows all commands
+ * alphabetically by key/character.
+ */
+class CommandSet {
+public:
+    CommandSet();
+
+    void attach(Window* window);
+    bool onKey(sk_app::Window::Key key, sk_app::Window::InputState state, uint32_t modifiers);
+    bool onChar(SkUnichar, uint32_t modifiers);
+
+    void addCommand(SkUnichar c, const char* group, const char* description,
+                    std::function<void(void)> function);
+    void addCommand(Window::Key k, const char* keyName, const char* group, const char* description,
+                    std::function<void(void)> function);
+
+    void drawHelp(SkCanvas* canvas);
+
+private:
+    struct Command {
+        enum CommandType {
+            kChar_CommandType,
+            kKey_CommandType,
+        };
+
+        Command(SkUnichar c, const char* group, const char* description,
+                std::function<void(void)> function)
+            : fType(kChar_CommandType)
+            , fChar(c)
+            , fKeyName(SkStringPrintf("%c", c))
+            , fGroup(group)
+            , fDescription(description)
+            , fFunction(function) {}
+
+        Command(Window::Key k, const char* keyName, const char* group, const char* description,
+                std::function<void(void)> function)
+            : fType(kKey_CommandType)
+            , fKey(k)
+            , fKeyName(keyName)
+            , fGroup(group)
+            , fDescription(description)
+            , fFunction(function) {}
+
+        CommandType fType;
+
+        // For kChar_CommandType
+        SkUnichar fChar;
+
+        // For kKey_CommandType
+        Window::Key fKey;
+
+        // Common to all command types
+        SkString fKeyName;
+        SkString fGroup;
+        SkString fDescription;
+        std::function<void(void)> fFunction;
+    };
+
+    static bool compareCommandKey(const Command& first, const Command& second);
+    static bool compareCommandGroup(const Command& first, const Command& second);
+
+    enum HelpMode {
+        kNone_HelpMode,
+        kGrouped_HelpMode,
+        kAlphabetical_HelpMode,
+    };
+
+    Window*           fWindow;
+    SkTArray<Command> fCommands;
+    HelpMode          fHelpMode;
+};
+
+}   // namespace sk_app
+
+#endif