Add shift mode support

README.md

@@ -165,6 +165,7 @@ These can then be added to your code, as shown in `devicedb.h`.
 - `HatToButtons`
 - `LatchedToMomentaryButton`
 - `MomentaryToLatchedButton`
+- `Shift`
 - `ShortPressLongPress`
 - `SquareDeadzone`
 
@@ -318,6 +319,20 @@ Does the exact opposite of `LatchedToMomentaryButton`: it converts a short press
 stick.Button1 >> MomentaryToLatchedButton() >> vj.Button1;
 ```
 
+## Shift
+
+Switches between actions, depending on an on/off state:
+
+```C++
+bool shifted = false;
+stick.Button15 >> &shifted;
+stick.Button16 >> Shift {
+  &shifted,
+  /* normal behavior */ vj.Button1,
+  /* shifted behavior */ vj.Button2,
+};
+```
+
 ## ShortPressLongPress
 
 This divides a button into two, depending on if a button is pressed and quickly released, or held for a moment.

lib/Shift.h

@@ -0,0 +1,46 @@
+/*
+ * Copyright (c) 2020-present, Fred Emmott <[email protected]>
+ * All rights reserved.
+ *
+ * This source code is licensed under the ISC license found in the LICENSE file
+ * in the root directory of this source tree.
+ */
+#pragma once
+
+#include "Sink.h"
+#include "SinkPtr.h"
+
+namespace fredemmott::inputmapping {
+
+template <control T>
+class Shift : public Sink<T> {
+ private:
+  bool* mShifted = nullptr;
+  SinkPtr<T> mA, mB;
+
+ public:
+  template <convertible_to_sink_ptr<T> A, convertible_to_sink_ptr<T> B>
+  Shift(bool* shifted, A&& a, B&& b)
+    : mShifted(shifted),
+      mA(convert_to_any_sink_ptr(std::forward<A>(a))),
+      mB(convert_to_any_sink_ptr(std::forward<B>(b))) {
+  }
+
+  virtual void map(typename T::Value value) override {
+    auto next = *mShifted ? mB : mA;
+    next->map(value);
+  }
+};
+
+// Help template inference along a bit...
+
+template <convertible_to_sink_ptr<Axis> A, convertible_to_sink_ptr<Axis> B>
+Shift(bool*, A, B) -> Shift<Axis>;
+
+template <convertible_to_sink_ptr<Button> A, convertible_to_sink_ptr<Button> B>
+Shift(bool*, A, B) -> Shift<Button>;
+
+template <convertible_to_sink_ptr<Hat> A, convertible_to_sink_ptr<Hat> B>
+Shift(bool*, A, B) -> Shift<Hat>;
+
+}// namespace fredemmott::inputmapping

lib/easymode.h

@@ -19,6 +19,7 @@
 #include "LatchedToMomentaryButton.h"
 #include "MomentaryToLatchedButton.h"
 #include "Profile.h"
+#include "Shift.h"
 #include "ShortPressLongPress.h"
 #include "SquareDeadzone.h"
 #include "connections.h"

tests/Shift_test.cpp

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2020-present, Fred Emmott <[email protected]>
+ * All rights reserved.
+ *
+ * This source code is licensed under the ISC license found in the LICENSE file
+ * in the root directory of this source tree.
+ */
+
+#include "Shift.h"
+
+#include "MappableVJoyOutput.h"
+#include "tests.h"
+
+using namespace fredemmott::inputmapping;
+
+TEST_CASE("Shift") {
+  bool shifted = false;
+  TestButton button;
+  bool a = false, b = false;
+
+  button >> Shift(&shifted, &a, &b);
+
+  button.emit(true);
+  REQUIRE(a);
+  REQUIRE(!b);
+
+  button.emit(false);
+  REQUIRE(!a);
+  REQUIRE(!b);
+
+  shifted = true;
+  button.emit(true);
+  REQUIRE(!a);
+  REQUIRE(b);
+}