Add LeaderPrefix custom plugin example sketch

Signed-off-by: Michael Richters <gedankenexperimenter@gmail.com>

examples/Keystrokes/LeaderPrefix/LeaderPrefix.ino

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+/* -*- mode: c++ -*-
+ * Kaleidoscope-LeaderPrefix -- Prefix arg for Leader plugin
+ * Copyright (C) 2021  Keyboard.io, Inc
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <Kaleidoscope.h>
+#include <Kaleidoscope-Leader.h>
+#include <Kaleidoscope-Macros.h>
+
+#include <Kaleidoscope-Ranges.h>
+#include "kaleidoscope/KeyEventTracker.h"
+#include "kaleidoscope/LiveKeys.h"
+#include "kaleidoscope/plugin.h"
+
+// *INDENT-OFF*
+KEYMAPS(
+  [0] = KEYMAP_STACKED
+  (Key_NoKey,    Key_1, Key_2, Key_3, Key_4, Key_5, Key_NoKey,
+   Key_Backtick, Key_Q, Key_W, Key_E, Key_R, Key_T, Key_Tab,
+   Key_PageUp,   Key_A, Key_S, Key_D, Key_F, Key_G,
+   Key_PageDown, Key_Z, Key_X, Key_C, Key_V, Key_B, Key_Escape,
+
+   Key_LeftControl, Key_Backspace, Key_LeftGui, Key_LeftShift,
+   LEAD(0),
+
+   Key_skip,  Key_6, Key_7, Key_8,     Key_9,      Key_0,         Key_skip,
+   Key_Enter, Key_Y, Key_U, Key_I,     Key_O,      Key_P,         Key_Equals,
+              Key_H, Key_J, Key_K,     Key_L,      Key_Semicolon, Key_Quote,
+   Key_skip,  Key_N, Key_M, Key_Comma, Key_Period, Key_Slash,     Key_Minus,
+
+   Key_RightShift, Key_RightAlt, Key_Spacebar, Key_RightControl,
+   LEAD(0)),
+)
+// *INDENT-ON*
+
+namespace kaleidoscope {
+namespace plugin {
+
+// =============================================================================
+/// Plugin to supply a numeric prefix argument to Leader key functions
+///
+/// This plugin lets the user type a numeric prefix after a Leader key is
+/// pressed, but before the rest of the Leader sequence is begun, storing the
+/// "prefix argument" and making it available to functions called from the
+/// leader dictionary.  LeaderPrefix allows us to define keys other than the
+/// ones on the number row to be interpreted as the "digit" keys, because
+/// whatever we use will need to be accessed without a layer change.
+class LeaderPrefix : public Plugin {
+ public:
+  // We need to define `onKeyswitchEvent()` instead of `onKeyEvent()` because we
+  // need to intercept events before Leader sees them, and the Leader plugin
+  // uses the former.
+  EventHandlerResult onKeyswitchEvent(KeyEvent &event) {
+    // Every `onKeyswitchEvent()` function should begin with this to prevent
+    // re-processing events that it has already seen.
+    if (event_tracker_.shouldIgnore(event))
+      return EventHandlerResult::OK;
+
+    // `Active` means that we're actively building the prefix argument.  If the
+    // plugin is not active, we're looking for a Leader key toggling on.
+    if (!active_) {
+      if (keyToggledOn(event.state) && isLeaderKey(event.key)) {
+        // A Leader key toggled on, so we set our state to "active", and set the
+        // arg value to zero.
+        active_ = true;
+        leader_arg_ = 0;
+      }
+      // Whether or not the plugin just became active, there's nothing more to
+      // do for this event.
+      return EventHandlerResult::OK;
+    }
+
+    // The plugin is "active", so we're looking for a "digit" key that just
+    // toggled on.
+    if (keyToggledOn(event.state)) {
+      // We search our array of digit keys to find one that matches the event.
+      // These "digit keys" are defined by their `KeyAddr` because they're
+      // probably independent of keymap and layer, and because a `KeyAddr` only
+      // takes one byte, whereas a `Key` takes two.
+      for (uint8_t i{0}; i < 10; ++i) {
+        if (digit_addrs_[i] == event.addr) {
+          // We found a match, which means that one of our "digit keys" toggled
+          // on.  If this happens more than once, the user is typing a number
+          // with multiple digits, so we multiply the current value by ten
+          // before adding the new digit to the total.
+          leader_arg_ *= 10;
+          leader_arg_ += i;
+          // Next, we mask the key that was just pressed, so that nothing will
+          // happen when it is released.
+          live_keys.mask(event.addr);
+          // We return `ABORT` so that no other plugins (i.e. Leader) will see
+          // this keypress event.
+          return EventHandlerResult::ABORT;
+        }
+      }
+    }
+    // No match was found, so the key that toggled on was not one of our "digit
+    // keys".  Presumably, this is the first key in the Leader sequence that is
+    // being typed.  We leave the prefix argument at its current value so that
+    // it will still be set when the sequence is finished, and allow the event
+    // to pass through to the next plugin (i.e. Leader).
+    active_ = false;
+    return EventHandlerResult::OK;
+  }
+
+  uint16_t arg() const {
+    return leader_arg_;
+  }
+
+ private:
+  // The "digit keys": these are the keys on the number row of the Model01.
+  KeyAddr digit_addrs_[10] = {
+    KeyAddr(0, 14), KeyAddr(0, 1), KeyAddr(0, 2), KeyAddr(0, 3), KeyAddr(0, 4),
+    KeyAddr(0, 5), KeyAddr(0, 10), KeyAddr(0, 11), KeyAddr(0, 12), KeyAddr(0, 13),
+  };
+
+  // This event tracker is necessary to prevent re-processing events.  Any
+  // plugin that defines `onKeyswitchEvent()` should use one.
+  KeyEventTracker event_tracker_;
+
+  // The current state of the plugin.  It determines whether we're looking for a
+  // Leader keypress or building a prefix argument.
+  bool active_{false};
+
+  // The prefix argument itself.
+  uint16_t leader_arg_{0};
+
+  // Leader should probably provide this test, but since it doesn't, we add it
+  // here to determine if a key is a Leader key.
+  bool isLeaderKey(Key key) {
+    return (key >= ranges::LEAD_FIRST && key <= ranges::LEAD_LAST);
+  }
+};
+
+} // namespace plugin
+} // namespace kaleidoscope
+
+// This creates our plugin object.
+kaleidoscope::plugin::LeaderPrefix LeaderPrefix;
+
+auto &serial_port = Kaleidoscope.serialPort();
+
+static void leaderTestX(uint8_t seq_index) {
+  serial_port.println(F("leaderTestX"));
+}
+
+static void leaderTestXX(uint8_t seq_index) {
+  serial_port.println(F("leaderTestXX"));
+}
+
+// This demonstrates how to use the prefix argument in a Leader function.  In
+// this case, our function just types as many `x` characters as specified by the
+// prefix arg.
+void leaderTestPrefix(uint8_t seq_index) {
+  // Read the prefix argument into a temporary variable:
+  uint8_t prefix_arg = LeaderPrefix.arg();
+  // Use a Macros helper function to tap the `X` key repeatedly.
+  while (prefix_arg-- > 0)
+    Macros.tap(Key_X);
+}
+
+static const kaleidoscope::plugin::Leader::dictionary_t leader_dictionary[] PROGMEM =
+LEADER_DICT({LEADER_SEQ(LEAD(0), Key_X), leaderTestX},
+{LEADER_SEQ(LEAD(0), Key_X, Key_X), leaderTestXX},
+{LEADER_SEQ(LEAD(0), Key_Z), leaderTestPrefix});
+
+// The order matters here; LeaderPrefix won't work unless it precedes Leader in
+// this list.  If there are other plugins in the list, these two should ideally
+// be next to each other, but that's not necessary.
+KALEIDOSCOPE_INIT_PLUGINS(LeaderPrefix, Leader);
+
+void setup() {
+  Kaleidoscope.setup();
+
+  Leader.dictionary = leader_dictionary;
+}
+
+void loop() {
+  Kaleidoscope.loop();
+}

examples/Keystrokes/LeaderPrefix/sketch.json

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+{
+  "cpu": {
+    "fqbn": "keyboardio:avr:model01",
+    "port": ""
+  }
+}