border: clear buffer on fullscreen views

This patch makes sure to clear the border buffer of fullscreen view so
the border doesn't get drawn behind a fullscreen view, which would be
visible if the view was transparent.

include/border.h

@@ -3,11 +3,19 @@
 #include <wlc/wlc.h>
 #include "container.h"
 
+/**
+ * Border pixel buffer and corresponding geometry.
+ */
 struct border {
 	unsigned char *buffer;
 	struct wlc_geometry geometry;
 };
 
+/**
+ * Clear border buffer.
+ */
+void border_clear(struct border *border);
+
 void render_view_borders(wlc_handle view);
 void update_view_border(swayc_t *view);
 void map_update_view_border(swayc_t *view, void *data);

sway/border.c

@@ -4,12 +4,11 @@
 #include <pango/pangocairo.h>
 #include <stdlib.h>
 #include <stdio.h>
+#include <arpa/inet.h>
 #include "container.h"
 #include "config.h"
 #include "client/pango.h"
 
-#include <arpa/inet.h>
-
 void cairo_set_source_u32(cairo_t *cairo, uint32_t color) {
 	color = htonl(color);
 
@@ -20,6 +19,13 @@ void cairo_set_source_u32(cairo_t *cairo, uint32_t color) {
 		(color >> (3*8) & 0xFF) / 255.0);
 }
 
+void border_clear(struct border *border) {
+	if (border && border->buffer) {
+		free(border->buffer);
+		border->buffer = NULL;
+	}
+}
+
 static cairo_t *create_border_buffer(swayc_t *view, struct wlc_geometry g, cairo_surface_t **surface) {
 	if (view->border == NULL) {
 		view->border = malloc(sizeof(struct border));
@@ -35,16 +41,14 @@ static cairo_t *create_border_buffer(swayc_t *view, struct wlc_geometry g, cairo
 	*surface = cairo_image_surface_create_for_data(view->border->buffer,
 			CAIRO_FORMAT_ARGB32, g.size.w, g.size.h, stride);
 	if (cairo_surface_status(*surface) != CAIRO_STATUS_SUCCESS) {
-		free(view->border);
-		view->border->buffer = NULL;
+		border_clear(view->border);
 		sway_log(L_DEBUG, "Unable to allocate surface");
 		return NULL;
 	}
 	cr = cairo_create(*surface);
 	if (cairo_status(cr) != CAIRO_STATUS_SUCCESS) {
 		cairo_surface_destroy(*surface);
-		free(view->border->buffer);
-		view->border->buffer = NULL;
+		border_clear(view->border);
 		sway_log(L_DEBUG, "Unable to create cairo context");
 		return NULL;
 	}
@@ -295,10 +299,8 @@ void update_view_border(swayc_t *view) {
 	cairo_t *cr = NULL;
 	cairo_surface_t *surface = NULL;
 
-	if (view->border && view->border->buffer) {
-		free(view->border->buffer);
-		view->border->buffer = NULL;
-	}
+	// clear previous border buffer.
+	border_clear(view->border);
 
 	// get focused and focused_inactive views
 	swayc_t *focused = get_focused_view(&root_container);

sway/layout.c

@@ -555,6 +555,7 @@ void update_geometry(swayc_t *container) {
 
 		container->border_geometry = wlc_geometry_zero;
 		container->title_bar_geometry = wlc_geometry_zero;
+		border_clear(container->border);
 	} else if (container->is_floating) { // allocate border for floating window
 		update_border_geometry_floating(container, &geometry);
 	} else if (!container->is_floating) { // allocate border for titled window