Use imagescroll feature.

regress/image-scroll-uses-region.sh

@@ -0,0 +1,20 @@
+#!/bin/sh
+
+# The PR's narrow-pane scroll check. Margins permit native scrolling;
+# without them imagescroll must not suppress a necessary repaint.
+# Different clients must make that decision independently.
+
+PATH=/bin:/usr/bin
+TERM=screen
+export TERM
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+
+python3 -B - "$TEST_TMUX" <<'PY'
+import sys
+from image_scroll import check_scroll, check_clients
+
+check_scroll(sys.argv[1], True, margins=True)
+check_scroll(sys.argv[1], True, margins=False)
+check_clients(sys.argv[1])
+check_clients(sys.argv[1], narrow=True)
+PY