Sanity check gaps between tiled containers

When the gaps become too large for the space available gracefully
reduced them all the way to 0 if needed.

Fixes #4294

include/sway/tree/node.h

@@ -3,6 +3,9 @@
 #include <stdbool.h>
 #include "list.h"
 
+#define MIN_SANE_W 100
+#define MIN_SANE_H 60
+
 struct sway_root;
 struct sway_output;
 struct sway_workspace;

sway/commands/resize.c

@@ -15,8 +15,6 @@
 #define AXIS_HORIZONTAL (WLR_EDGE_LEFT | WLR_EDGE_RIGHT)
 #define AXIS_VERTICAL   (WLR_EDGE_TOP | WLR_EDGE_BOTTOM)
 
-static const int MIN_SANE_W = 100, MIN_SANE_H = 60;
-
 enum resize_unit {
 	RESIZE_UNIT_PX,
 	RESIZE_UNIT_PPT,

sway/tree/arrange.c

@@ -68,7 +68,10 @@ static void apply_horiz_layout(list_t *children, struct wlr_box *parent) {
 		}
 		temp = temp->parent;
 	}
-	double child_total_width = parent->width - inner_gap * (children->length - 1);
+	double total_gap = fmin(inner_gap * (children->length - 1),
+		fmax(0, parent->width - MIN_SANE_W * children->length));
+	double child_total_width = parent->width - total_gap;
+	inner_gap = total_gap / (children->length - 1);
 
 	// Resize windows
 	sway_log(SWAY_DEBUG, "Arranging %p horizontally", parent);
@@ -143,7 +146,10 @@ static void apply_vert_layout(list_t *children, struct wlr_box *parent) {
 		}
 		temp = temp->parent;
 	}
-	double child_total_height = parent->height - inner_gap * (children->length - 1);
+	double total_gap = fmin(inner_gap * (children->length - 1),
+		fmax(0, parent->height - MIN_SANE_H * children->length));
+	double child_total_height = parent->height - total_gap;
+	inner_gap = total_gap / (children->length - 1);
 
 	// Resize windows
 	sway_log(SWAY_DEBUG, "Arranging %p vertically", parent);