Antecedent Morph Behavior aka Adaptive Keys

app/CMakeLists.txt

@@ -55,6 +55,7 @@ if ((NOT CONFIG_ZMK_SPLIT) OR CONFIG_ZMK_SPLIT_ROLE_CENTRAL)
   target_sources_ifdef(CONFIG_ZMK_BEHAVIOR_MACRO app PRIVATE src/behaviors/behavior_macro.c)
   target_sources(app PRIVATE src/behaviors/behavior_momentary_layer.c)
   target_sources(app PRIVATE src/behaviors/behavior_mod_morph.c)
+  target_sources(app PRIVATE src/behaviors/behavior_antecedent_morph.c)
   target_sources(app PRIVATE src/behaviors/behavior_outputs.c)
   target_sources(app PRIVATE src/behaviors/behavior_toggle_layer.c)
   target_sources(app PRIVATE src/behaviors/behavior_to_layer.c)

app/dts/bindings/behaviors/zmk,behavior-antecedent-morph.yaml

@@ -0,0 +1,23 @@
+# Copyright (c) 2023 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+description: Antecedent Morph Behavior
+
+compatible: "zmk,behavior-antecedent-morph"
+
+include: zero_param.yaml
+
+properties:
+  defaults:
+    type: phandle-array
+    required: true
+    specifier-space: binding
+  bindings:
+    type: phandle-array
+    required: true
+  antecedents:
+    type: array
+    required: true
+  max-delay-ms:
+    type: int
+    default: -1

app/src/behaviors/behavior_antecedent_morph.c

@@ -0,0 +1,228 @@
+/*
+ * Copyright (c) 2023 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#define DT_DRV_COMPAT zmk_behavior_antecedent_morph
+
+#include <zephyr/device.h>
+#include <drivers/behavior.h>
+#include <zephyr/logging/log.h>
+#include <zmk/behavior.h>
+
+#include <zmk/keymap.h>
+#include <zmk/event_manager.h>
+#include <zmk/events/keycode_state_changed.h>
+#include <zmk/hid.h>
+
+LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
+
+#if DT_HAS_COMPAT_STATUS_OKAY(DT_DRV_COMPAT)
+
+// configuration struct per instance
+struct behavior_antecedent_morph_config {
+  int                          serial;          // serial number of the instance of this behavior
+  uint32_t                     max_delay_ms;    // maximum delay between key release and successive key press for the adaptive behavior
+  size_t                       defaults_len;    // length of the array of default behaviors (must be 1)
+  struct zmk_behavior_binding *defaults;        // array of default behaviors
+  size_t                       bindings_len;    // length of the array of morphed behaviors
+  struct zmk_behavior_binding *bindings;        // array of morphed behaviors
+  int32_t                      antecedents_len; // length of the array of antecedents (key codes)
+  int32_t                      antecedents[];   // array of antecedents (key codes)
+};
+
+// data struct per instance
+struct behavior_antecedent_morph_data {
+  struct zmk_behavior_binding *pressed_binding; // the actual behavior that was pressed by the adaptive behavior
+};
+
+// data shared by all instances
+static int32_t code_pressed; // most recently pressed key code (with implicit mods, usage page and keycode)
+static int64_t time_pressed; // time stamp in milli-seconds of that key press
+
+static int antecedent_morph_keycode_state_changed_listener(const zmk_event_t *eh);
+
+ZMK_LISTENER(behavior_antecedent_morph, antecedent_morph_keycode_state_changed_listener);
+ZMK_SUBSCRIPTION(behavior_antecedent_morph,zmk_keycode_state_changed);
+
+// Capture all key press and release events in order to record the most recently released key code.
+//
+// Note that the event structure gives us the keycode (16 bit), the usage page (8 bit) and the implicit modifiers (8
+// bit), but not the explicit modifiers. If the keymap contains the binding "&kp RA(Y)", for example, then right-alt is
+// an implicit modifier so that instead of the Y, the special character Ü is sent (US International layout).
+//
+// Whether the user is holding down a shift key at that moment, however, i.e. the explicit modifiers, is not known. We
+// could reconstruct this information by tracking the press and release events of the modifier keys (keycodes higher
+// than 0xe0) though, but in the present version, the potential antecedents are recorded without modifiers.
+//
+// We here record all key release events of non-modifier keys (keycodes less than 0xe0).
+//
+// If someone somewhere triggers a key down event with an illegal key code (beyond 0xff), this key code is recorded as a
+// potential antecedent, but is then discarded. This way, it is possible to trigger 'silent antecedents', e.g. in order
+// to create new dead keys.
+
+static int antecedent_morph_keycode_state_changed_listener(const zmk_event_t *eh) {
+
+  struct zmk_keycode_state_changed *ev = as_zmk_keycode_state_changed(eh);
+
+  int32_t code = ((ev->implicit_modifiers & 0xff) << 24) | ((ev->usage_page & 0xff) << 16) | (ev->keycode & 0xffff);
+
+  LOG_DBG("%s keycode %d; page %d; implicit mods %d; explicit mods %d; key code 0x%08x",ev->state ? "down" : "up",ev->keycode,ev->usage_page,ev->implicit_modifiers,ev->explicit_modifiers,code);
+  if ((ev->state) && ((ev->keycode < 0xe0) || (ev->keycode > 0xff))) {
+    LOG_DBG("global <code_pressed> variable changes from 0x%08x to 0x%08x",code_pressed,code);
+    code_pressed = code;
+    time_pressed = ev->timestamp;
+  }
+
+  if (ev->keycode > 0xff) {
+    LOG_DBG("event dropped");
+    return(ZMK_EV_EVENT_HANDLED);
+  } else {
+    return(ZMK_EV_EVENT_BUBBLE);
+  }
+}
+
+// When an antecedent morph binding is pressed, we test whether the most recently released key code is among the
+// configured antecedents and whether the corresponding key release event was no more than the configured delay time
+// ago.
+
+static int on_antecedent_morph_binding_pressed(struct zmk_behavior_binding *binding,
+					       struct zmk_behavior_binding_event event) {
+  const struct device *dev = zmk_behavior_get_binding(binding->behavior_dev);
+  const struct behavior_antecedent_morph_config *cfg = dev->config;
+  struct behavior_antecedent_morph_data *data = dev->data;
+  int morph = -1;
+
+  LOG_DBG("press zmk,behavior-antecedent-morph serial no. %d when <code_pressed> is 0x%08x; delay %dms; and explicit_mods 0x%02x",
+	  cfg->serial,code_pressed,(int32_t)(event.timestamp-time_pressed),zmk_hid_get_explicit_mods());
+
+  if (data->pressed_binding != NULL) {
+    LOG_ERR("Can't press the same antecedent-morph twice");
+    return -ENOTSUP;
+  }
+
+  for (int i=0;i<cfg->antecedents_len;i++) {
+    if (code_pressed == cfg->antecedents[i]) {
+      morph = i;
+    }
+  }
+
+  if ((morph >= 0) && ((int32_t)(event.timestamp-time_pressed)) < cfg->max_delay_ms) {
+
+    // If the the delay between the most recent key release and the pressing of the current behavior is less than the
+    // configured maximum delay and if the most recently released key is among the recorded antecedents, issue the
+    // behavior among the 'bindings' that is at the corresponding position to the antecedent among the 'antecedents'.
+    //
+    // Note that should one of the arrays 'bindings' or 'defaults' are too short, an error is triggered and the behavior
+    // never pressed.
+
+    LOG_DBG("morph condition satisfied");
+
+    if (morph < cfg->bindings_len) {
+      data->pressed_binding = (struct zmk_behavior_binding *)&cfg->bindings[morph];
+    } else {
+      LOG_ERR("Property 'bindings' must be an array at least of length %d.",morph+1);
+      return -ENOTSUP;
+    }
+
+  } else {
+
+    // Otherwise, issue the first behavior of the 'defaults' array.
+
+    if (0 < cfg->defaults_len) {
+      data->pressed_binding = (struct zmk_behavior_binding *)&cfg->defaults[0];
+    } else {
+      LOG_ERR("Property 'defaults' must be an array at least of length 1.");
+      return -ENOTSUP;
+    }
+  }
+
+  return zmk_behavior_invoke_binding(data->pressed_binding,event,true);
+}
+
+// The release of the antecedent morph behavior considers the behavior that was recorded in the instance data and
+// releases it.
+
+static int on_antecedent_morph_binding_released(struct zmk_behavior_binding *binding,
+						struct zmk_behavior_binding_event event) {
+  const struct device *dev = zmk_behavior_get_binding(binding->behavior_dev);
+  const struct behavior_antecedent_morph_config *cfg = dev->config;
+  struct behavior_antecedent_morph_data *data = dev->data;
+
+  if (data->pressed_binding == NULL) {
+    LOG_ERR("Antecedent-morph already released");
+    return -ENOTSUP;
+  }
+
+  LOG_DBG("release zmk,behavior-antecedent-morph serial no. %d",cfg->serial);
+
+  struct zmk_behavior_binding *pressed_binding = data->pressed_binding;
+  data->pressed_binding = NULL;
+  return zmk_behavior_invoke_binding(pressed_binding,event,false);
+}
+
+static const struct behavior_driver_api behavior_antecedent_morph_driver_api = {
+  .binding_pressed = on_antecedent_morph_binding_pressed,
+  .binding_released = on_antecedent_morph_binding_released,
+};
+
+static int behavior_antecedent_morph_init(const struct device *dev) {
+
+  const struct behavior_antecedent_morph_config *cfg = dev->config;
+  struct behavior_antecedent_morph_data *data = dev->data;
+
+  LOG_DBG("zmk,behavior-antecedent-morph serial no. %d defined with %d defaults, %d bindings and %d antecedents.",cfg->serial,cfg->defaults_len,cfg->bindings_len,cfg->antecedents_len);
+  for (int i=0; i<cfg->antecedents_len;i++) {
+    LOG_DBG("antedecent no. %d is 0x%08x.",i,cfg->antecedents[i]);
+  }
+
+  data->pressed_binding = NULL;
+  code_pressed = 0;
+  return 0;
+}
+
+#define ZMK_KEYMAP_EXTRACT_DEFAULT(idx, drv_inst)                                                  \
+    {                                                                                              \
+        .behavior_dev = DEVICE_DT_NAME(DT_PHANDLE_BY_IDX(drv_inst, defaults, idx)),                \
+        .param1 = COND_CODE_0(DT_PHA_HAS_CELL_AT_IDX(drv_inst, defaults, idx, param1), (0),        \
+                              (DT_PHA_BY_IDX(drv_inst, defaults, idx, param1))),                   \
+        .param2 = COND_CODE_0(DT_PHA_HAS_CELL_AT_IDX(drv_inst, defaults, idx, param2), (0),        \
+                              (DT_PHA_BY_IDX(drv_inst, defaults, idx, param2))),                   \
+    }
+
+#define _TRANSFORM_ENTRY_DEFAULT(idx, node) ZMK_KEYMAP_EXTRACT_DEFAULT(idx, node)
+
+#define TRANSFORMED_DEFAULTS(node)					                                              \
+  { LISTIFY(DT_INST_PROP_LEN(node, defaults), _TRANSFORM_ENTRY_DEFAULT, (, ), DT_DRV_INST(node)) }
+
+#define _TRANSFORM_ENTRY_BINDING(idx, node) ZMK_KEYMAP_EXTRACT_BINDING(idx, node)
+
+#define TRANSFORMED_BINDINGS(node)					                                              \
+  { LISTIFY(DT_INST_PROP_LEN(node, bindings), _TRANSFORM_ENTRY_BINDING, (, ), DT_DRV_INST(node)) }
+
+#define KP_INST(n)							                                              \
+  static struct zmk_behavior_binding behavior_antecedent_morph_config_##n##_defaults[DT_INST_PROP_LEN(n, defaults)] = \
+    TRANSFORMED_DEFAULTS(n);						                                              \
+  static struct zmk_behavior_binding behavior_antecedent_morph_config_##n##_bindings[DT_INST_PROP_LEN(n, bindings)] = \
+    TRANSFORMED_BINDINGS(n);						                                              \
+  static struct behavior_antecedent_morph_config behavior_antecedent_morph_config_##n = {                             \
+    .serial = n,							                                              \
+    .max_delay_ms = DT_INST_PROP(n, max_delay_ms),			                                              \
+    .defaults = behavior_antecedent_morph_config_##n##_defaults,	                                              \
+    .defaults_len = DT_INST_PROP_LEN(n, defaults),			                                              \
+    .bindings = behavior_antecedent_morph_config_##n##_bindings,                                                      \
+    .bindings_len = DT_INST_PROP_LEN(n, bindings),			                                              \
+    .antecedents = DT_INST_PROP(n, antecedents),			                                              \
+    .antecedents_len = DT_INST_PROP_LEN(n, antecedents)                                                               \
+  };									                                              \
+  static struct behavior_antecedent_morph_data behavior_antecedent_morph_data_##n = {                                 \
+  };									                                              \
+  BEHAVIOR_DT_INST_DEFINE(n,behavior_antecedent_morph_init,NULL,&behavior_antecedent_morph_data_##n,   		      \
+			&behavior_antecedent_morph_config_##n,		                                              \
+			POST_KERNEL, CONFIG_KERNEL_INIT_PRIORITY_DEFAULT,                                             \
+			&behavior_antecedent_morph_driver_api);
+
+DT_INST_FOREACH_STATUS_OKAY(KP_INST)
+
+#endif

docs/docs/keymaps/behaviors/antecedent-morph.md

@@ -0,0 +1,115 @@
+---
+title: Antecedent-Morph Behavior
+sidebar_label: Antecedent-Morph
+---
+
+## Summary
+
+The Antecedent-Morph behavior (adaptive keys) sends different behaviors, depending on which key was most recently
+released before the antecedent-morph behavior was pressed, if this occurs within a configurable time period.
+
+## Antecedent-Morph
+
+The configuration of the behavior consists of an array of `antecedents`, key codes with implicit modifiers, as well as
+of a delay `max-delay-ms` in milli-seconds. If none of the `antecedents` was released during the `max-delay-ms` before
+the antecedent-morph behavior is pressed, the behavior invokes the `defaults` binding. If, however, the `n`-th of the
+key codes (with implicit modifiers) listed in the array `antecedents` was released within `max-delay-ms`, the behavior
+invokes the `n`-th of the bindings of the `bindings` property.
+
+### Configuration
+
+If the key A is assigned the behavior `&ad_a` defined as follows, for example,
+
+```dts
+/ {
+    behaviors {
+        ad_a: adaptive_a {
+            compatible = "zmk,behavior-antecedent-morph";
+            label = "ADAPTIVE_A";
+            #binding-cells = <0>;
+			defaults = <&kp A>;
+            bindings = <&kp U>, <&kp O>;
+			antecedents = <Q Z>;
+			max-delay-ms = <250>;
+        };
+    };
+};
+```
+
+then by default, pressing this key issues the key press `&kp A`. But if it is preceded within 250 milli-seconds by Q or
+Z, then `&kp U` or `&kp O`, respectively, are issued instead.
+
+### Behavior Binding
+
+- Reference: `&ad_a`
+- Parameter: None
+
+Example:
+
+```dts
+&ad_a
+```
+
+### Behaviors
+
+The antecedent-morph behavior can issue not only key press events, but rather arbitrary behaviors.
+
+### Implicit Modifiers
+
+Some special key codes can be obtained only with the help of modifiers. For example, on the U.S. International Keyboard,
+the symbol Ü is obtained by holding right Alt and tapping Y. In order to issue this symbol, one can therefore use `&kp
+RA(Y)`. Here, right Alt is called an *implicit modifier*. Antecedents are always considered with implicit modifiers. For
+example,
+
+```dts
+/ {
+    behaviors {
+        ad_a: adaptive_a {
+            compatible = "zmk,behavior-antecedent-morph";
+            label = "ADAPTIVE_A";
+            #binding-cells = <0>;
+			defaults = <&kp A>;
+            bindings = <&kp U>, <&kp O>;
+			antecedents = <RA(Y) Z>;
+			max-delay-ms = <250>;
+        };
+    };
+};
+```
+
+replaces the A by a U if preceded by Ü, but not if preceded by Y.
+
+### Explicit Modifiers
+
+The entire function of the antecedent-morph behavior is independent of the *explicit modifiers*. These are the modifiers
+that the user is holding down while tapping the antecedent or while pressing the antecedent-morph behavior. In the above
+example, A is replaced by O if preceded by Z, regardless of which modifier keys were held down while tapping the Z,
+i.e. in particular after a lower case z or after an upper case Z.
+
+Finally, if the user is still holding down a Shift key when pressing the A that triggers the above antecedent-morph
+behavior, then this results in an upper case O rather than a lower case o.
+
+### Dead Antecedents
+
+If some binding somewhere issues an illegal key code in the range beyond 0x00ff, this illegal key code is recognized and
+tested as an antecedent, but then immediately discarded from the event queue. It therefore functions similarly to a dead
+key. Note that these illegal key codes are specified with the *usage page* 0x07 as in the following example. If some key
+is bound to `&kp DEAD_ANTE`, then it does not print anything, but still turns a subsequent A into a U.
+
+```dts
+#define DEAD_ANTE 0x070100
+
+/ {
+    behaviors {
+        ad_a: adaptive_a {
+            compatible = "zmk,behavior-antecedent-morph";
+            label = "ADAPTIVE_A";
+            #binding-cells = <0>;
+			defaults = <&kp A>;
+            bindings = <&kp U>, <&kp O>;
+			antecedents = <DEAD_ANTE Z>;
+			max-delay-ms = <250>;
+        };
+    };
+};
+```