From befe66d93f34e040312afdc3d34e3055cc7f0dec Mon Sep 17 00:00:00 2001
From: Consolatis <35009135+Consolatis@users.noreply.github.com>
Date: Sat, 26 Feb 2022 01:21:39 +0100
Subject: [PATCH] cursor.c: Keep sending adjusted motion events while button is
 pressed

This allows to keep dragging a scrollbar or selecting text even when
moving outside of the window. Fixes #241
---
 include/labwc.h | 12 ++++++++++++
 src/cursor.c    | 16 ++++++++++++++++
 src/xdg.c       |  3 +++
 src/xwayland.c  |  3 +++
 4 files changed, 34 insertions(+)

diff --git a/include/labwc.h b/include/labwc.h
index 43ce6d2d..07909228 100644
--- a/include/labwc.h
+++ b/include/labwc.h
@@ -82,6 +82,18 @@ struct seat {
 	/* if set, views cannot receive focus */
 	struct wlr_layer_surface_v1 *focused_layer;
 
+	/**
+	 * active_view will usually be NULL and is only set on button press
+	 * while the mouse is over a view surface and reset to NULL on button
+	 * release.
+	 * It is used to send cursor motion events to a surface even though
+	 * the cursor has left the surface in the meantime.
+	 *
+	 * This allows to keep dragging a scrollbar or selecting text even
+	 * when moving outside of the window.
+	 */
+	struct view *active_view;
+
 	struct wl_client *active_client_while_inhibited;
 	struct wl_list inputs;
 	struct wl_listener new_input;
diff --git a/src/cursor.c b/src/cursor.c
index a3590eab..29e8eb5f 100644
--- a/src/cursor.c
+++ b/src/cursor.c
@@ -195,6 +195,15 @@ process_cursor_motion(struct server *server, uint32_t time)
 	} else if (server->input_mode == LAB_INPUT_STATE_RESIZE) {
 		process_cursor_resize(server, time);
 		return;
+	} else if (server->seat.active_view && !server->seat.drag_icon) {
+		/* Button has been pressed while over a view surface */
+		struct view *view = server->seat.active_view;
+		double sx = server->seat.cursor->x - view->x;
+		double sy = server->seat.cursor->y - view->y;
+		sx = sx < 0 ? 0 : (sx > view->w ? view->w : sx);
+		sy = sy < 0 ? 0 : (sy > view->h ? view->h : sy);
+		wlr_seat_pointer_notify_motion(server->seat.seat, time, sx, sy);
+		return;
 	}
 
 	/* Otherwise, find view under the pointer and send the event along */
@@ -317,6 +326,7 @@ start_drag(struct wl_listener *listener, void *data)
 {
 	struct seat *seat = wl_container_of(listener, seat, start_drag);
 	struct wlr_drag *wlr_drag = data;
+	seat->active_view = NULL;
 	seat->drag_icon = wlr_drag->icon;
 	wl_signal_add(&seat->drag_icon->events.destroy, &seat->destroy_drag);
 }
@@ -647,6 +657,8 @@ cursor_button(struct wl_listener *listener, void *data)
 
 	/* handle _release_ */
 	if (event->state == WLR_BUTTON_RELEASED) {
+		server->seat.active_view = NULL;
+
 		if (server->input_mode == LAB_INPUT_STATE_MENU) {
 			if (close_menu) {
 				if (server->menu_current) {
@@ -674,6 +686,10 @@ cursor_button(struct wl_listener *listener, void *data)
 	}
 
 	/* Handle _press */
+	if (view_area == LAB_SSD_CLIENT) {
+		server->seat.active_view = view;
+	}
+
 	if (server->input_mode == LAB_INPUT_STATE_MENU) {
 		if (view_area != LAB_SSD_MENU) {
 			/* We close the menu on release so we don't leak a stray release */
diff --git a/src/xdg.c b/src/xdg.c
index dc534499..2e01a3c9 100644
--- a/src/xdg.c
+++ b/src/xdg.c
@@ -85,6 +85,9 @@ handle_destroy(struct wl_listener *listener, void *data)
 		wlr_foreign_toplevel_handle_v1_destroy(view->toplevel_handle);
 	}
 	interactive_end(view);
+	if (view->server->seat.active_view == view) {
+		view->server->seat.active_view = NULL;
+	}
 	wl_list_remove(&view->link);
 	wl_list_remove(&view->destroy.link);
 	if (view->scene_tree) {
diff --git a/src/xwayland.c b/src/xwayland.c
index a3da7b90..88f8c5f0 100644
--- a/src/xwayland.c
+++ b/src/xwayland.c
@@ -99,6 +99,9 @@ handle_destroy(struct wl_listener *listener, void *data)
 		wlr_foreign_toplevel_handle_v1_destroy(view->toplevel_handle);
 	}
 	interactive_end(view);
+	if (view->server->seat.active_view == view) {
+		view->server->seat.active_view = NULL;
+	}
 	view->xwayland_surface = NULL;
 	wl_list_remove(&view->link);
 	wl_list_remove(&view->map.link);