From 244dc5897de8ef9d415aa208216406e5767b9420 Mon Sep 17 00:00:00 2001
From: Andrew Hamilton <and_hamilton@yahoo.com>
Date: Fri, 21 Jan 2022 08:59:29 +1000
Subject: [PATCH] diff-edit: Allow negative scroll positions in portals

---
 fill3/fill3/__init__.py   | 14 ++++++++++----
 fill3/tests/fill3_test.py |  7 +++++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/fill3/fill3/__init__.py b/fill3/fill3/__init__.py
index af3bd54..d56f32d 100755
--- a/fill3/fill3/__init__.py
+++ b/fill3/fill3/__init__.py
@@ -229,12 +229,18 @@ class Portal:
         width, height = dimensions
         x, y = self.position
         try:
-            appearance = self.widget.appearance_interval((y, y+height))
+            appearance = self.widget.appearance_interval((max(y, 0), y+height))
         except AttributeError:
-            appearance = self.widget.appearance()[y:y+height]
+            appearance = self.widget.appearance()[max(y, 0):y+height]
         self.last_dimensions = dimensions
-        return appearance_resize([row[x:x+width] for row in appearance],
-                                 dimensions, self.background_char)
+        top = [self.background_char * width] * -y if y < 0 else []
+        bottom = appearance_resize([row[max(x, 0):x+width] for row in appearance],
+                                    (width + min(x, 0), height + min(y, 0)),
+                                   self.background_char)
+        if x < 0:
+            padding = self.background_char * -x
+            bottom = [padding + line for line in bottom]
+        return top + bottom
 
 
 class View:
diff --git a/fill3/tests/fill3_test.py b/fill3/tests/fill3_test.py
index c6711c4..856c980 100755
--- a/fill3/tests/fill3_test.py
+++ b/fill3/tests/fill3_test.py
@@ -38,6 +38,13 @@ class WidgetTests(unittest.TestCase):
         self.assert_string(portal.appearance_for((5, 1)), "oobar")
         portal.position = (0, 10)
         self.assert_string(portal.appearance_for((1, 1)), " ")
+        portal.position = (1, 0)
+        self.assert_string(portal.appearance_for((6, 2)), "oobar \n      ")
+        portal.position = (-1, -1)
+        self.assert_string(portal.appearance_for((2, 2)), "  \n f")
+        self.assert_string(portal.appearance_for((8, 3)), "        \n foobar \n        ")
+        portal.position = (5, 0)
+        self.assert_string(portal.appearance_for((2, 1)), "r ")
 
     def test_border_widget(self):
         contents = fill3.Filler(self.TEXT_A)