text: #define _POSIX_C_SOURCE 200809L
  #include <float.h>
  #include <wlr/types/wlr_cursor.h>
  #include "sway/input/cursor.h"
  #include "sway/input/seat.h"
  #include "sway/tree/view.h"
  #include "log.h"
  
  struct seatop_down_event {
  	struct sway_container *con;
  	double ref_lx, ref_ly;         // cursor's x/y at start of op
  	double ref_con_lx, ref_con_ly; // container's x/y at start of op
  };
  
  static void handle_pointer_axis(struct sway_seat *seat,
  		struct wlr_event_pointer_axis *event) {
  	struct sway_input_device *input_device =
  		event->device ? event->device->data : NULL;
  	struct input_config *ic =
  		input_device ? input_device_get_config(input_device) : NULL;
  	float scroll_factor =
  		(ic == NULL || ic->scroll_factor == FLT_MIN) ? 1.0f : ic->scroll_factor;
  
  	wlr_seat_pointer_notify_axis(seat->wlr_seat, event->time_msec,
  		event->orientation, scroll_factor * event->delta,
  		round(scroll_factor * event->delta_discrete), event->source);
  }
  
  static void handle_button(struct sway_seat *seat, uint32_t time_msec,
  		struct wlr_input_device *device, uint32_t button,
  		enum wlr_button_state state) {
  	seat_pointer_notify_button(seat, time_msec, button, state);
  
  	if (seat->cursor->pressed_button_count == 0) {
  		seatop_begin_default(seat);
  	}
  }
  
  static void handle_pointer_motion(struct sway_seat *seat, uint32_t time_msec,
  		double dx, double dy) {
  	struct seatop_down_event *e = seat->seatop_data;
  	struct sway_container *con = e->con;
  	if (seat_is_input_allowed(seat, con->view->surface)) {
  		double moved_x = seat->cursor->cursor->x - e->ref_lx;
  		double moved_y = seat->cursor->cursor->y - e->ref_ly;
  		double sx = e->ref_con_lx + moved_x;
  		double sy = e->ref_con_ly + moved_y;
  		wlr_seat_pointer_notify_motion(seat->wlr_seat, time_msec, sx, sy);
  	}
  }
  
  static void handle_unref(struct sway_seat *seat, struct sway_container *con) {
  	struct seatop_down_event *e = seat->seatop_data;
  	if (e->con == con) {
  		seatop_begin_default(seat);
  	}
  }
  
  static const struct sway_seatop_impl seatop_impl = {
  	.button = handle_button,
  	.pointer_motion = handle_pointer_motion,
  	.pointer_axis = handle_pointer_axis,
  	.unref = handle_unref,
  	.allow_set_cursor = true,
  };
  
  void seatop_begin_down(struct sway_seat *seat, struct sway_container *con,
  		uint32_t time_msec, int sx, int sy) {
  	seatop_end(seat);
  
  	struct seatop_down_event *e =
  		calloc(1, sizeof(struct seatop_down_event));
  	if (!e) {
  		return;
  	}
  	e->con = con;
  	e->ref_lx = seat->cursor->cursor->x;
  	e->ref_ly = seat->cursor->cursor->y;
  	e->ref_con_lx = sx;
  	e->ref_con_ly = sy;
  
  	seat->seatop_impl = &seatop_impl;
  	seat->seatop_data = e;
  
  	container_raise_floating(con);
  }
  