[Docs] New section to modifier docs: Checking Modifier State (#10550)
* Added new section to docs: Checking Modifier State * Added id anchors to all headers in modifiers docs * Added a Wikipedia link to bitwise operators and... crosslinked to the QMK macro docs. * Added an explanation on the format of mod bitmask * Added .md extension to hyperlinks to macros docs * Corrected mod mask order and changed notation * Documented add_oneshot_mods and del_oneshot_mods * Mentioned modifier checks in the macro docs * Explained strict modifier checking i.e. using `get_mods() & MOD_MASK == MOD_MASK` instead of simply `get_mods() & MOD_MASK` * Added (un)register_mods to the docs * Put left term of comparison in parens
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@ -23,6 +23,141 @@ These allow you to combine a modifier with a keycode. When pressed, the keydown
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You can also chain them, for example `LCTL(LALT(KC_DEL))` or `C(A(KC_DEL))` makes a key that sends Control+Alt+Delete with a single keypress.
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# Checking Modifier State :id=checking-modifier-state
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The current modifier state can mainly be accessed with two functions: `get_mods()` for normal modifiers and modtaps and `get_oneshot_mods()` for one-shot modifiers (unless they're held, in which case they act like normal modifier keys).
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The presence of one or more specific modifiers in the current modifier state can be detected by ANDing the modifier state with a mod mask corresponding to the set of modifiers you want to match for. The reason why bitwise operators are used is that the modifier state is stored as a single byte in the format (GASC)<sub>R</sub>(GASC)<sub>L</sub>.
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Thus, to give an example, `01000010` would be the internal representation of LShift+RAlt.
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For more information on bitwise operators in C, click [here](https://en.wikipedia.org/wiki/Bitwise_operations_in_C) to open the Wikipedia page on the topic.
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In practice, this means that you can check whether a given modifier is active with `get_mods() & MOD_BIT(KC_<modifier>)` (see the [list of modifier keycodes](keycodes_basic.md#modifiers)) or with `get_mods() & MOD_MASK_<modifier>` if the difference between left and right hand modifiers is not important and you want to match both. Same thing can be done for one-shot modifiers if you replace `get_mods()` with `get_oneshot_mods()`.
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To check that *only* a specific set of mods is active at a time, AND the modifier state and your desired mod mask as explained above and compare the result to the mod mask itself: `get_mods() & <mod mask> == <mod mask>`.
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For example, let's say you want to trigger a piece of custom code if one-shot left control and one-shot left shift are on but every other one-shot mods are off. To do so, you can compose the desired mod mask by combining the mod bits for left control and shift with `(MOD_BIT(KC_LCTL) | MOD_BIT(KC_LSFT))` and then plug it in: `get_oneshot_mods & (MOD_BIT(KC_LCTL) | MOD_BIT(KC_LSFT)) == (MOD_BIT(KC_LCTL) | MOD_BIT(KC_LSFT))`. Using `MOD_MASK_CS` instead for the mod bitmask would have forced you to press four modifier keys (both versions of control and shift) to fulfill the condition.
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The full list of mod masks is as follows:
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| Mod Mask Name | Matching Modifiers |
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|--------------------|------------------------------------------------|
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| `MOD_MASK_CTRL` | LCTRL , RCTRL |
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| `MOD_MASK_SHIFT` | LSHIFT , RSHIFT |
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| `MOD_MASK_ALT` | LALT , RALT |
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| `MOD_MASK_GUI` | LGUI , RGUI |
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| `MOD_MASK_CS` | CTRL , SHIFT |
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| `MOD_MASK_CA` | (L/R)CTRL , (L/R)ALT |
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| `MOD_MASK_CG` | (L/R)CTRL , (L/R)GUI |
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| `MOD_MASK_SA` | (L/R)SHIFT , (L/R)ALT |
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| `MOD_MASK_SG` | (L/R)SHIFT , (L/R)GUI |
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| `MOD_MASK_AG` | (L/R)ALT , (L/R)GUI |
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| `MOD_MASK_CSA` | (L/R)CTRL , (L/R)SHIFT , (L/R)ALT |
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| `MOD_MASK_CSG` | (L/R)CTRL , (L/R)SHIFT , (L/R)GUI |
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| `MOD_MASK_CAG` | (L/R)CTRL , (L/R)ALT , (L/R)GUI |
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| `MOD_MASK_SAG` | (L/R)SHIFT , (L/R)ALT , (L/R)GUI |
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| `MOD_MASK_CSAG` | (L/R)CTRL , (L/R)SHIFT , (L/R)ALT , (L/R)GUI |
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Aside from accessing the currently active modifiers using `get_mods()`, there exists some other functions you can use to modify the modifier state, where the `mods` argument refers to the modifiers bitmask.
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* `add_mods(mods)`: Enable `mods` without affecting any other modifiers
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* `register_mods(mods)`: Like `add_mods` but send a keyboard report immediately.
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* `del_mods(mods)`: Disable `mods` without affecting any other modifiers
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* `unregister_mods(mods)`: Like `del_mods` but send a keyboard report immediately.
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* `set_mods(mods)`: Overwrite current modifier state with `mods`
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* `clear_mods()`: Reset the modifier state by disabling all modifiers
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Similarly, in addition to `get_oneshot_mods()`, there also exists these functions for one-shot mods:
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* `add_oneshot_mods(mods)`: Enable `mods` without affecting any other one-shot modifiers
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* `del_oneshot_mods(mods)`: Disable `mods` without affecting any other one-shot modifiers
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* `set_oneshot_mods(mods)`: Overwrite current one-shot modifier state with `mods`
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* `clear_oneshot_mods()`: Reset the one-shot modifier state by disabling all one-shot modifiers
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## Examples :id=examples
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The following examples use [advanced macro functions](feature_macros.md#advanced-macro-functions) which you can read more about in the [documentation page on macros](feature_macros.md).
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### Alt + Escape for Alt + Tab :id=alt-escape-for-alt-tab
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Simple example where chording Left Alt with `KC_ESC` makes it behave like `KC_TAB` for alt-tabbing between applications. This example strictly checks if only Left Alt is active, meaning you can't do Alt+Shift+Esc to switch between applications in reverse order. Also keep in mind that this removes the ability to trigger the actual Alt+Escape keyboard shortcut, though it keeps the ability to do AltGr+Escape.
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```c
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bool process_record_user(uint16_t keycode, keyrecord_t *record) {
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switch (keycode) {
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case KC_ESC:
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// Detect the activation of only Left Alt
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if ((get_mods() & MOD_BIT(KC_LALT)) == MOD_BIT(KC_LALT)) {
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if (record->event.pressed) {
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// No need to register KC_LALT because it's already active.
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// The Alt modifier will apply on this KC_TAB.
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register_code(KC_TAB);
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} else {
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unregister_code(KC_TAB);
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}
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// Do not let QMK process the keycode further
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return false;
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}
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// Else, let QMK process the KC_ESC keycode as usual
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return true;
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}
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return true;
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};
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```
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### Shift + Backspace for Delete :id=shift-backspace-for-delete
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Advanced example where the original behaviour of shift is cancelled when chorded with `KC_BSPC` and is instead fully replaced by `KC_DEL`. Two main variables are created to make this work well: `mod_state` and `delkey_registered`. The first one stores the modifier state and is used to restore it after registering `KC_DEL`. The second variable is a boolean variable (true or false) which keeps track of the status of `KC_DEL` to manage the release of the whole Backspace/Delete key correctly.
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As opposed to the previous example, this doesn't use strict modifier checking. Pressing `KC_BSPC` while one or two shifts are active is enough to trigger this custom code, regardless of the state of other modifiers. That approach offers some perks: Ctrl+Shift+Backspace lets us delete the next word (Ctrl+Delete) and Ctrl+Alt+Shift+Backspace lets us execute the Ctrl+Alt+Del keyboard shortcut.
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```c
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// Initialize variable holding the binary
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// representation of active modifiers.
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uint8_t mod_state;
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bool process_record_user(uint16_t keycode, keyrecord_t *record) {
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// Store the current modifier state in the variable for later reference
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mod_state = get_mods();
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switch (keycode) {
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case KC_BSPC:
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{
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// Initialize a boolean variable that keeps track
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// of the delete key status: registered or not?
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static bool delkey_registered;
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if (record->event.pressed) {
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// Detect the activation of either shift keys
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if (mod_state & MOD_MASK_SHIFT) {
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// First temporarily canceling both shifts so that
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// shift isn't applied to the KC_DEL keycode
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del_mods(MOD_MASK_SHIFT);
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register_code(KC_DEL);
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// Update the boolean variable to reflect the status of KC_DEL
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delkey_registered = true;
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// Reapplying modifier state so that the held shift key(s)
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// still work even after having tapped the Backspace/Delete key.
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set_mods(mod_state);
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return false;
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}
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} else { // on release of KC_BSPC
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// In case KC_DEL is still being sent even after the release of KC_BSPC
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if (delkey_registered) {
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unregister_code(KC_DEL);
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delkey_registered = false;
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return false;
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}
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}
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// Let QMK process the KC_BSPC keycode as usual outside of shift
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return true;
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}
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}
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return true;
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};
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```
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# Legacy Content :id=legacy-content
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This page used to encompass a large set of features. We have moved many sections that used to be part of this page to their own pages. Everything below this point is simply a redirect so that people following old links on the web find what they're looking for.
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@ -209,7 +209,7 @@ SEND_STRING(".."SS_TAP(X_END));
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There are some functions you may find useful in macro-writing. Keep in mind that while you can write some fairly advanced code within a macro, if your functionality gets too complex you may want to define a custom keycode instead. Macros are meant to be simple.
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?> You can also use the functions described in [Useful functions](ref_functions.md) for additional functionality. For example `reset_keyboard()` allows you to reset the keyboard as part of a macro.
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?> You can also use the functions described in [Useful function](ref_functions.md) and [Checking modifier state](feature_advanced_keycodes#checking-modifier-state) for additional functionality. For example, `reset_keyboard()` allows you to reset the keyboard as part of a macro and `get_mods() & MOD_MASK_SHIFT` lets you check for the existence of active shift modifiers.
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### `record->event.pressed`
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