Add a keymap with a scrolling mode for the Ploopy Nano trackball

keyboards/ploopyco/trackball_nano/keymaps/maddie/keymap.c

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+/* Copyright 2021 Colin Lam (Ploopy Corporation)
+ * Copyright 2020 Christopher Courtney, aka Drashna Jael're  (@drashna) <drashna@live.com>
+ * Copyright 2019 Sunjun Kim
+ * Copyright 2019 Hiroyuki Okada
+ *
+ * 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
+
+// safe range starts at `PLOOPY_SAFE_RANGE` instead.
+uint8_t scroll_enabled = 0;
+uint8_t lock_state = 0;
+int16_t delta_x = 0;
+int16_t delta_y = 0;
+
+void process_mouse_user(report_mouse_t *mouse_report, int16_t x, int16_t y) {
+	if (scroll_enabled) {
+		delta_x += x;
+		delta_y += y;
+
+		if (delta_x > 60) {
+			mouse_report->h = 1;
+			delta_x = 0;
+		} else if (delta_x < -60) {
+			mouse_report->h = -1;
+			delta_x = 0;
+		}
+
+		if (delta_y > 15) {
+			mouse_report->v = -1;
+			delta_y = 0;
+		} else if (delta_y < -15) {
+			mouse_report->v = 1;
+			delta_y = 0;
+		}
+	} else {
+		mouse_report->x = x;
+		mouse_report->y = y;
+	}
+}
+
+void keyboard_post_init_user(void) {
+	lock_state = host_keyboard_led_state().num_lock;
+}
+
+bool led_update_user(led_t led_state) {
+	static uint8_t lock_count = 0;
+	static uint16_t scroll_timer = 0;
+
+	if (timer_elapsed(scroll_timer) > 25) {
+		scroll_timer = timer_read();
+		lock_count = 0;
+	}
+
+	if (led_state.num_lock != lock_state) {
+		lock_count++;
+
+		if (lock_count == 2) {
+			scroll_enabled = !scroll_enabled;
+			lock_count = 0;
+			delta_x = 0;
+			delta_y = 0;
+		}
+	}
+
+	lock_state = led_state.num_lock;
+	return true;
+}

keyboards/ploopyco/trackball_nano/keymaps/maddie/readme.md

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+toggles scroll mode when numlock is double-tapped within 25ms. add a macro or something, unless you have ungodly fast fingers.