Limit inner gaps to sensible values

Large inner gaps can lead to broken rendering with width/height going
negative. Limit the gaps so that they never make the windows smaller
than a minimum sensible size (the same used for the resize command).

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;

include/util.h

@@ -34,4 +34,9 @@ const char *sway_wl_output_subpixel_to_string(enum wl_output_subpixel subpixel);
 
 bool set_cloexec(int fd, bool cloexec);
 
+#undef MAX
+#define MAX(a, b)  (((a) > (b)) ? (a) : (b))
+#undef MIN
+#define MIN(a, b)  (((a) < (b)) ? (a) : (b))
+
 #endif

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/sway.5.scd

@@ -568,6 +568,9 @@ The default colors are:
 	This affects new workspaces only, and is used when the workspace doesn't
 	have its own gaps settings (see: workspace <ws> gaps ...).
 
+	If the gaps are too large and would make a view too narrow or short they
+	are adjusted to be smaller or even removed for that specific view.
+
 *hide_edge_borders* [--i3] none|vertical|horizontal|both|smart|smart_no_gaps
 	Hides window borders adjacent to the screen edges. Default is _none_. The
 	_--i3_ option enables i3-compatible behavior to hide the title bar on tabbed

sway/tree/container.c

@@ -1226,13 +1226,17 @@ void container_add_gaps(struct sway_container *c) {
 		}
 	}
 
-	int gaps1 = ws->gaps_inner / 2;
-	int gaps2 = ws->gaps_inner - gaps1;
+	int gaps_horizontal = MAX(0, MIN(ws->gaps_inner, c->width - MIN_SANE_W));
+	int gaps_horizontal1 = gaps_horizontal / 2;
+	int gaps_horizontal2 = gaps_horizontal - gaps_horizontal1;
+	c->current_gaps.left = gaps_horizontal1;
+	c->current_gaps.right = gaps_horizontal2;
 
-	c->current_gaps.top = gaps1;
-	c->current_gaps.bottom = gaps2;
-	c->current_gaps.left = gaps1;
-	c->current_gaps.right = gaps2;
+	int gaps_vertical = MAX(0, MIN(ws->gaps_inner, c->height - MIN_SANE_H));
+	int gaps_vertical1 = gaps_vertical / 2;
+	int gaps_vertical2 = gaps_vertical - gaps_vertical1;
+	c->current_gaps.top = gaps_vertical1;
+	c->current_gaps.bottom = gaps_vertical2;
 
 	c->x += c->current_gaps.left;
 	c->y += c->current_gaps.top;

sway/tree/workspace.c

@@ -746,15 +746,19 @@ void workspace_add_gaps(struct sway_workspace *ws) {
 	} else {
 		// For tiled containers we need to add the half-gap all around the edge
 		// to match the half gaps that the children have all already added around
-		// themselves. We use the opposite gaps1/gaps2 order so that the sum adds
-		// up to the correct total gap size in all circumstances.
-		int gaps1 = ws->gaps_inner / 2;
-		int gaps2 = ws->gaps_inner - gaps1;
+		// themselves. We use the opposite order for the two halves so that the
+		// sum adds up to the correct total gap size in all circumstances.
+		int gaps_horizontal = MAX(0, MIN(ws->gaps_inner, ws->width - MIN_SANE_W));
+		int gaps_horizontal1 = gaps_horizontal / 2;
+		int gaps_horizontal2 = gaps_horizontal - gaps_horizontal1;
+		ws->current_gaps.left += gaps_horizontal2;
+		ws->current_gaps.right += gaps_horizontal1;
 
-		ws->current_gaps.top += gaps2;
-		ws->current_gaps.bottom += gaps1;
-		ws->current_gaps.left += gaps2;
-		ws->current_gaps.right += gaps1;
+		int gaps_vertical = MAX(0, MIN(ws->gaps_inner, ws->height - MIN_SANE_H));
+		int gaps_vertical1 = gaps_vertical / 2;
+		int gaps_vertical2 = gaps_vertical - gaps_vertical1;
+		ws->current_gaps.top += gaps_vertical2;
+		ws->current_gaps.bottom += gaps_vertical1;
 	}
 
 	ws->x += ws->current_gaps.left;