rootston: fix urxvt damage on HiDPI outputs

util/region: add wlr_region_expand

include/wlr/util/region.h

@@ -19,4 +19,11 @@ void wlr_region_scale(pixman_region32_t *dst, pixman_region32_t *src,
 void wlr_region_transform(pixman_region32_t *dst, 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.
+ */
+void wlr_region_expand(pixman_region32_t *dst, pixman_region32_t *src,
+	int distance);
+
 #endif

rootston/output.c

@@ -600,6 +600,12 @@ static void damage_from_surface(struct wlr_surface *surface,
 	pixman_region32_init(&damage);
 	pixman_region32_copy(&damage, &surface->current->surface_damage);
 	wlr_region_scale(&damage, &damage, output->wlr_output->scale);
+	if (ceil(output->wlr_output->scale) > surface->current->scale) {
+		// When scaling up a surface, it'll become blurry so we need to expand
+		// the damage region
+		wlr_region_expand(&damage, &damage,
+			ceil(output->wlr_output->scale) - surface->current->scale);
+	}
 	pixman_region32_translate(&damage, box.x, box.y);
 	pixman_region32_union(&output->damage, &output->damage, &damage);
 	pixman_region32_fini(&damage);

util/region.c

@@ -101,3 +101,30 @@ void wlr_region_transform(pixman_region32_t *dst, pixman_region32_t *src,
 	pixman_region32_init_rects(dst, dst_rects, nrects);
 	free(dst_rects);
 }
+
+void wlr_region_expand(pixman_region32_t *dst, pixman_region32_t *src,
+		int distance) {
+	if (distance == 0) {
+		pixman_region32_copy(dst, src);
+		return;
+	}
+
+	int nrects;
+	pixman_box32_t *src_rects = pixman_region32_rectangles(src, &nrects);
+
+	pixman_box32_t *dst_rects = malloc(nrects * sizeof(pixman_box32_t));
+	if (dst_rects == NULL) {
+		return;
+	}
+
+	for (int i = 0; i < nrects; ++i) {
+		dst_rects[i].x1 = src_rects[i].x1 - distance;
+		dst_rects[i].x2 = src_rects[i].x2 + distance;
+		dst_rects[i].y1 = src_rects[i].y1 - distance;
+		dst_rects[i].y2 = src_rects[i].y2 + distance;
+	}
+
+	pixman_region32_fini(dst);
+	pixman_region32_init_rects(dst, dst_rects, nrects);
+	free(dst_rects);
+}