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`.

10 files changed, 91 insertions, 2 deletions

diff --git a/include/sway/commands.h b/include/sway/commands.h
index 0e2d7931..7d0ff838 100644
--- a/include/sway/commands.h
+++ b/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;
diff --git a/include/sway/config.h b/include/sway/config.h
index f604b054..ebf16e6a 100644
--- a/include/sway/config.h
+++ b/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;
diff --git a/include/sway/input/seat.h b/include/sway/input/seat.h
index d665c86e..a3c20346 100644
--- a/include/sway/input/seat.h
+++ b/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);
 
diff --git a/sway/commands.c b/sway/commands.c
index 927434bc..0883b57b 100644
--- a/sway/commands.c
+++ b/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 },
diff --git a/sway/commands/tiling_drag_threshold.c b/sway/commands/tiling_drag_threshold.c
new file mode 100644
index 00000000..6b0531c3
--- /dev/null
+++ b/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);
+}
diff --git a/sway/config.c b/sway/config.c
index bb7f796d..5d631b7e 100644
--- a/sway/config.c
+++ b/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;
diff --git a/sway/input/cursor.c b/sway/input/cursor.c
index f8302ddf..516251f7 100644
--- a/sway/input/cursor.c
+++ b/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;
         }
 
diff --git a/sway/input/seat.c b/sway/input/seat.c
index fa82c9ce..9422713d 100644
--- a/sway/input/seat.c
+++ b/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;
diff --git a/sway/meson.build b/sway/meson.build
index 7f739287..98676ce0 100644
--- a/sway/meson.build
+++ b/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',
diff --git a/sway/sway.5.scd b/sway/sway.5.scd
index e6abef56..37a9b24c 100644
--- a/sway/sway.5.scd
+++ b/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