3 files changed, 112 insertions, 0 deletions
diff --git a/users/cameronjlarsen/features/oneshot.c b/users/cameronjlarsen/features/oneshot.c
new file mode 100644
index 0000000000..799b7c1aa2
--- /dev/null
+++ b/users/cameronjlarsen/features/oneshot.c
@@ -0,0 +1,66 @@
+/* Copyright 2022 Cameron Larsen <camjlarsen@gmail.com>
+ *
+ * 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, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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 "oneshot.h"
+
+void update_oneshot(oneshot_state *state, uint16_t mod, uint16_t trigger, uint16_t keycode, keyrecord_t *record) {
+    if (keycode == trigger) {
+        if (record->event.pressed) {
+            // Trigger keydown
+            if (*state == os_up_unqueued) {
+                register_code(mod);
+            }
+            *state = os_down_unused;
+        } else {
+            // Trigger keyup
+            switch (*state) {
+                case os_down_unused:
+                    // If we didn't use the mod while trigger was held, queue it.
+                    *state = os_up_queued;
+                    break;
+                case os_down_used:
+                    // If we did use the mod while trigger was held, unregister it.
+                    *state = os_up_unqueued;
+                    unregister_code(mod);
+                    break;
+                default:
+                    break;
+            }
+        }
+    } else {
+        if (record->event.pressed) {
+            if (is_oneshot_cancel_key(keycode) && *state != os_up_unqueued) {
+                // Cancel oneshot on designated cancel keydown.
+                *state = os_up_unqueued;
+                unregister_code(mod);
+            }
+        } else {
+            if (!is_oneshot_ignored_key(keycode)) {
+                // On non-ignored keyup, consider the oneshot used.
+                switch (*state) {
+                    case os_down_unused:
+                        *state = os_down_used;
+                        break;
+                    case os_up_queued:
+                        *state = os_up_unqueued;
+                        unregister_code(mod);
+                        break;
+                    default:
+                        break;
+                }
+            }
+        }
+    }
+}
diff --git a/users/cameronjlarsen/features/oneshot.h b/users/cameronjlarsen/features/oneshot.h
new file mode 100644
index 0000000000..7fac7b5d58
--- /dev/null
+++ b/users/cameronjlarsen/features/oneshot.h
@@ -0,0 +1,41 @@
+// The GPLv2 License (GPLv2)
+//
+// Copyright (c) 2022 Cameron Larsen
+//
+// 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; either version 2 of the License, or
+// (at your option) any later version.
+//
+// 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/>.
+#pragma once
+
+#include QMK_KEYBOARD_H
+
+// Represents the four states a oneshot key can be in
+typedef enum {
+    os_up_unqueued,
+    os_up_queued,
+    os_down_unused,
+    os_down_used,
+} oneshot_state;
+
+// Custom oneshot mod implementation that doesn't rely on timers. If a mod is
+// used while it is held it will be unregistered on keyup as normal, otherwise
+// it will be queued and only released after the next non-mod keyup.
+void update_oneshot(oneshot_state *state, uint16_t mod, uint16_t trigger, uint16_t keycode, keyrecord_t *record);
+
+// To be implemented by the consumer. Defines keys to cancel oneshot mods.
+bool is_oneshot_cancel_key(uint16_t keycode);
+
+// To be implemented by the consumer. Defines keys to ignore when determining
+// whether a oneshot mod has been used. Setting this to modifiers and layer
+// change keys allows stacking multiple oneshot modifiers, and carrying them
+// between layers.
+bool is_oneshot_ignored_key(uint16_t keycode);
diff --git a/users/cameronjlarsen/rules.mk b/users/cameronjlarsen/rules.mk
new file mode 100644
index 0000000000..59d14ca61f
--- /dev/null
+++ b/users/cameronjlarsen/rules.mk
@@ -0,0 +1,5 @@
+CUSTOM_ONESHOT_ENABLE ?= no
+ifeq ($(strip $(CUSTOM_ONESHOT_ENABLE)), yes)
+    SRC += $(USER_PATH)/features/oneshot.c
+    OPT_DEFS += -DCUSTOM_ONESHOT_ENABLE
+endif