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-rw-r--r--include/wlr/util/region.h4
-rw-r--r--util/region.c2
2 files changed, 4 insertions, 2 deletions
diff --git a/include/wlr/util/region.h b/include/wlr/util/region.h
index c3f1cbe8..948307a1 100644
--- a/include/wlr/util/region.h
+++ b/include/wlr/util/region.h
@@ -39,8 +39,8 @@ void wlr_region_transform(pixman_region32_t *dst, const pixman_region32_t *src,
enum wl_output_transform transform, int width, int height);
/**
- * Expands the region of `distance`. If `distance` is negative, it shrinks the
- * region.
+ * Expands the region by distance on both axis. distance must be
+ * a non-negative number.
*/
void wlr_region_expand(pixman_region32_t *dst, const pixman_region32_t *src,
int distance);
diff --git a/util/region.c b/util/region.c
index a3b13e06..b74c55e5 100644
--- a/util/region.c
+++ b/util/region.c
@@ -111,6 +111,8 @@ void wlr_region_transform(pixman_region32_t *dst, const pixman_region32_t *src,
void wlr_region_expand(pixman_region32_t *dst, const pixman_region32_t *src,
int distance) {
+ assert(distance >= 0);
+
if (distance == 0) {
pixman_region32_copy(dst, src);
return;