QMK Highlight Keys with Keycodes

/*  https://www.reddit.com/r/olkb/comments/12wg84s/is_there_a_way_to_determine_if_a_key_is_bound_or/
 *  QMK code to set the color of the LEDs on keys that have a keycode assigned to them, on certain layers.
 *  Replace _MODLAYER1 and _MODLAYER2 with the names or numbers of your desired layers.
 *  Replace RGB_GREEN and RGB_MAGENTA with the desired color for each layer.
 *  This can be a named color from https://github.com/qmk/qmk_firmware/blob/master/quantum/color.h
 *    or 3 separate values for red, green, and blue.  e.g. highlight_bound_keys(_MODLAYER1, 0, 255, 0);
 *
 *  This can go into keymap.c
 */


void highlight_bound_keys(uint8_t layer, uint8_t red, uint8_t green, uint8_t blue) {
    for (uint8_t row = 0; row < MATRIX_ROWS; row++) {
        for (uint8_t col = 0; col < MATRIX_COLS; col++) {
            uint8_t led_index;
            // Returns false if there is no LED at this key position
            // Otherwise, it writes the index of the LED to the given variable
            if (!rgb_matrix_map_row_column_to_led(row, col, &led_index))
                continue;  // Skip any key with no led

            // If the current key has a keycode assigned to it, set the LED to the given color
            // If the key is KC_NO or KC_TRANSPARENT, set the LED color to black/off
            if (keycode_at_keymap_location(layer, row, col) > KC_TRANSPARENT) {
                rgb_matrix_set_color(led_index, red, green, blue);
            } else {
                rgb_matrix_set_color(led_index, RGB_OFF);
            }
        }
    }
}

bool rgb_matrix_indicators_advanced_user(uint8_t led_min, uint8_t led_max) {
    switch(get_highest_layer(layer_state)) {
        case _MODLAYER1:                                    // if _MODLAYER1 is the top active layer
            highlight_bound_keys(_MODLAYER1, RGB_GREEN);    // highlight keys that have keycodes with the color GREEN
            break;
        case _MODLAYER2:                                    // if _MODLAYER2 is the top active layer
            highlight_bound_keys(_MODLAYER2, RGB_MAGENTA);  // highlight keys that have keycodes with the color MAGENTA
            break;
    }
    return true;
}