Implement tiling_drag_threshold

Implements `tiling_drag_threshold <threshold>` to prevent accidental
dragging of tiling containers. If a container (and all of its
descendants) are unfocused and the tile bar is pressed, a threshold
will be used before actually starting the drag. Once the threshold has
been exceeded, the cursor will change to the grab icon and the operation
will switch from `OP_MOVE_TILING_THRESHOLD` to `OP_MOVE_TILING`.

include/sway/commands.h

@@ -172,6 +172,7 @@ sway_cmd cmd_swaybg_command;
 sway_cmd cmd_swaynag_command;
 sway_cmd cmd_swap;
 sway_cmd cmd_tiling_drag;
+sway_cmd cmd_tiling_drag_threshold;
 sway_cmd cmd_title_align;
 sway_cmd cmd_title_format;
 sway_cmd cmd_titlebar_border_thickness;

include/sway/config.h

@@ -426,7 +426,9 @@ struct sway_config {
 	bool auto_back_and_forth;
 	bool show_marks;
 	enum alignment title_align;
+
 	bool tiling_drag;
+	int tiling_drag_threshold;
 
 	bool smart_gaps;
 	int gaps_inner;

include/sway/input/seat.h

@@ -39,6 +39,7 @@ enum sway_seat_operation {
 	OP_NONE,
 	OP_DOWN,
 	OP_MOVE_FLOATING,
+	OP_MOVE_TILING_THRESHOLD,
 	OP_MOVE_TILING,
 	OP_RESIZE_FLOATING,
 	OP_RESIZE_TILING,
@@ -186,6 +187,9 @@ void seat_begin_down(struct sway_seat *seat, struct sway_container *con,
 void seat_begin_move_floating(struct sway_seat *seat,
 		struct sway_container *con, uint32_t button);
 
+void seat_begin_move_tiling_threshold(struct sway_seat *seat,
+		struct sway_container *con, uint32_t button);
+
 void seat_begin_move_tiling(struct sway_seat *seat,
 		struct sway_container *con, uint32_t button);
 

sway/commands.c

@@ -87,6 +87,7 @@ static struct cmd_handler handlers[] = {
 	{ "smart_borders", cmd_smart_borders },
 	{ "smart_gaps", cmd_smart_gaps },
 	{ "tiling_drag", cmd_tiling_drag },
+	{ "tiling_drag_threshold", cmd_tiling_drag_threshold },
 	{ "title_align", cmd_title_align },
 	{ "titlebar_border_thickness", cmd_titlebar_border_thickness },
 	{ "titlebar_padding", cmd_titlebar_padding },

sway/commands/tiling_drag_threshold.c

@@ -0,0 +1,22 @@
+#include <string.h>
+#include "sway/commands.h"
+#include "sway/config.h"
+#include "log.h"
+
+struct cmd_results *cmd_tiling_drag_threshold(int argc, char **argv) {
+	struct cmd_results *error = NULL;
+	if ((error = checkarg(argc, "tiling_drag_threshold", EXPECTED_EQUAL_TO, 1))) {
+		return error;
+	}
+
+	char *inv;
+	int value = strtol(argv[0], &inv, 10);
+	if (*inv != '\0' || value < 0) {
+		return cmd_results_new(CMD_INVALID, "tiling_drag_threshold",
+			"Invalid threshold specified");
+	}
+
+	config->tiling_drag_threshold = value;
+
+	return cmd_results_new(CMD_SUCCESS, NULL, NULL);
+}

sway/config.c

@@ -233,6 +233,7 @@ static void config_defaults(struct sway_config *config) {
 	config->show_marks = true;
 	config->title_align = ALIGN_LEFT;
 	config->tiling_drag = true;
+	config->tiling_drag_threshold = 9;
 
 	config->smart_gaps = false;
 	config->gaps_inner = 0;

sway/input/cursor.c

@@ -384,6 +384,30 @@ static void handle_move_tiling_motion(struct sway_seat *seat,
 	desktop_damage_box(&seat->op_drop_box);
 }
 
+static void handle_move_tiling_threshold_motion(struct sway_seat *seat,
+		struct sway_cursor *cursor) {
+	double cx = seat->cursor->cursor->x;
+	double cy = seat->cursor->cursor->y;
+	double sx = seat->op_ref_lx;
+	double sy = seat->op_ref_ly;
+
+	// Get the scaled threshold for the output. Even if the operation goes
+	// across multiple outputs of varying scales, just use the scale for the
+	// output that the cursor is currently on for simplicity.
+	struct wlr_output *wlr_output = wlr_output_layout_output_at(
+			root->output_layout, cx, cy);
+	double output_scale = wlr_output ? wlr_output->scale : 1;
+	double threshold = config->tiling_drag_threshold * output_scale;
+	threshold *= threshold;
+
+	// If the threshold has been exceeded, start the actual drag
+	if ((cx - sx) * (cx - sx) + (cy - sy) * (cy - sy) > threshold) {
+		seat->operation = OP_MOVE_TILING;
+		cursor_set_image(cursor, "grab", NULL);
+		handle_move_tiling_motion(seat, cursor);
+	}
+}
+
 static void calculate_floating_constraints(struct sway_container *con,
 		int *min_width, int *max_width, int *min_height, int *max_height) {
 	if (config->floating_minimum_width == -1) { // no minimum
@@ -640,6 +664,9 @@ void cursor_send_pointer_motion(struct sway_cursor *cursor,
 		case OP_MOVE_FLOATING:
 			handle_move_floating_motion(seat, cursor);
 			break;
+		case OP_MOVE_TILING_THRESHOLD:
+			handle_move_tiling_threshold_motion(seat, cursor);
+			break;
 		case OP_MOVE_TILING:
 			handle_move_tiling_motion(seat, cursor);
 			break;
@@ -984,12 +1011,22 @@ void dispatch_cursor_button(struct sway_cursor *cursor,
 	if (config->tiling_drag && (mod_pressed || on_titlebar) &&
 			state == WLR_BUTTON_PRESSED && !is_floating_or_child &&
 			cont && !cont->is_fullscreen) {
-		if (on_titlebar) {
+		struct sway_container *focus = seat_get_focused_container(seat);
+		bool focused = focus == cont || container_has_ancestor(focus, cont);
+		if (on_titlebar && !focused) {
 			node = seat_get_focus_inactive(seat, &cont->node);
 			seat_set_focus(seat, node);
 		}
+
 		seat_pointer_notify_button(seat, time_msec, button, state);
-		seat_begin_move_tiling(seat, cont, button);
+
+		// If moving a previously unfocused container by it's title bar, use a
+		// threshold for the drag.
+		if (!mod_pressed && !focused && config->tiling_drag_threshold > 0) {
+			seat_begin_move_tiling_threshold(seat, cont, button);
+		} else {
+			seat_begin_move_tiling(seat, cont, button);
+		}
 		return;
 	}
 

sway/input/seat.c

@@ -1052,6 +1052,17 @@ void seat_begin_move_floating(struct sway_seat *seat,
 	cursor_set_image(seat->cursor, "grab", NULL);
 }
 
+void seat_begin_move_tiling_threshold(struct sway_seat *seat,
+		struct sway_container *con, uint32_t button) {
+	seat->operation = OP_MOVE_TILING_THRESHOLD;
+	seat->op_container = con;
+	seat->op_button = button;
+	seat->op_target_node = NULL;
+	seat->op_target_edge = 0;
+	seat->op_ref_lx = seat->cursor->cursor->x;
+	seat->op_ref_ly = seat->cursor->cursor->y;
+}
+
 void seat_begin_move_tiling(struct sway_seat *seat,
 		struct sway_container *con, uint32_t button) {
 	seat->operation = OP_MOVE_TILING;

sway/meson.build

@@ -89,6 +89,7 @@ sway_sources = files(
 	'commands/swaynag_command.c',
 	'commands/swap.c',
 	'commands/tiling_drag.c',
+	'commands/tiling_drag_threshold.c',
 	'commands/title_align.c',
 	'commands/title_format.c',
 	'commands/titlebar_border_thickness.c',

sway/sway.5.scd

@@ -572,6 +572,15 @@ The default colors are:
 	the _floating\_mod_ will also allow the container to be dragged. _toggle_
 	should not be used in the config file.
 
+*tiling\_drag\_threshold* <threshold>
+	Sets the threshold that must be exceeded for an unfocused tiling container
+	to be dragged by its titlebar. This has no effect if _floating\_mod_ is
+	used, if the container is focused, or if _tiling\_drag_ is set to
+	_disable_. Once the threshold has been exceeded once, the drag starts and
+	the cursor can come back inside the threshold without stopping the drag.
+	_threshold_ is multiplied by the scale of the output that the cursor on.
+	The default is 9.
+
 *title\_align* left|center|right
 	Sets the title alignment. If _right_ is selected and _show\_marks_ is set
 	to _yes_, the marks will be shown on the _left_ side instead of the