My ploopy configuration with some back/forward helpers & ad-hoc and permanent drag-scrolling support

config.h

/* Copyright 2023 Andreas Fuchs <asf@boinkor.net>
 *
 * 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

#define DYNAMIC_KEYMAP_LAYER_COUNT 8

/* defaults to 1600 DPI */
#define PLOOPY_DPI_OPTIONS                                                     \
  { 1200, 1700, 2400 }
#define PLOOPY_DPI_DEFAULT 1

/* Drag scrolling - invert V axis, set to a fixed amount of DPI */
#define PLOOPY_DRAGSCROLL_INVERT
#define PLOOPY_DRAGSCROLL_FIXED
#define PLOOPY_DRAGSCROLL_DPI 200

/* Number of points scrolled after which a click-scroll-release counts as
   "active while held". Scroll further than that in any direction & releasing
   the button deactivates drag scrolling.

   This number is pretty small to let us discern between "accidental"
   nudges of the ball when I meant to activate the mode, vs. small
   amount of scroll. */
#define BOINKOR_PLOOPY_RELEASE_ADHOC_DISTANCE 5

keymap.c

/* Copyright 2023 Andreas Fuchs <asf@boinkor.net>
 *
 * 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 QMK_KEYBOARD_H

extern bool is_drag_scroll;
uint16_t overall_scroll_distance = 0;

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
    [0] = LAYOUT(
        /* Base */
        KC_BTN1, KC_BTN3, KC_BTN2, MO(1), DRAG_SCROLL),
    [1] = LAYOUT(
        /* current-tab-based nav */
        LCMD(KC_LEFT_BRACKET), LCMD(KC_W), LCMD(KC_RIGHT_BRACKET), _______,
        MO(2)),
    [2] = LAYOUT(
        /* tab-bar nav */
        LCMD(LSFT(KC_LEFT_BRACKET)), _______, LCMD(LSFT(KC_RIGHT_BRACKET)),
        _______, _______),
    [3] = LAYOUT(_______, _______, _______, _______, _______),

    /* unused layers */
    [4] = LAYOUT(_______, _______, _______, _______, _______),
    [5] = LAYOUT(_______, _______, _______, _______, _______),
    [6] = LAYOUT(_______, _______, _______, _______, _______),
    [7] = LAYOUT(_______, _______, _______, _______, _______),
};

bool process_record_user(uint16_t keycode, keyrecord_t *record) {
  /* Specially handle l/r clicks on drag-scrolling (stop scrolling & reset DPI)
   */
  if (is_drag_scroll && (keycode == KC_BTN1 || keycode == KC_BTN2)) {
    is_drag_scroll = false;
    pointing_device_set_cpi(dpi_array[keyboard_config.dpi_config]);
    return false;
  }

  if (is_drag_scroll && keycode == DRAG_SCROLL && !record->event.pressed &&
      overall_scroll_distance > BOINKOR_PLOOPY_RELEASE_ADHOC_DISTANCE) {
    /* If we scrolled further than that distance while holding the
       button pressed, it's an adhoc scroll & we clear the
       drag-scroll state. */
    is_drag_scroll = false;
    pointing_device_set_cpi(dpi_array[keyboard_config.dpi_config]);
    return false;
  }

  return true;
}

report_mouse_t pointing_device_task_user(report_mouse_t mouse_report) {
  if (is_drag_scroll) {
    overall_scroll_distance += abs(mouse_report.v) + abs(mouse_report.h);
  } else {
    overall_scroll_distance = 0;
  }
  return mouse_report;
}