From e7771a21d94f56ab9a17c01bc37fab66845a9575 Mon Sep 17 00:00:00 2001
From: Simon Tatham <anakin@pobox.com>
Date: Fri, 12 Feb 2021 17:50:47 +0000
Subject: [PATCH] Fix missing recalculation of window border.

If you open a Windows PuTTY session and press Win+Right, Windows
auto-sizes the terminal window to cover the right-hand half of the
screen. Then if you press Win+Up it will be auto-sized again, this
time to the top right quadrant. In the second resize (if you don't
have font-based resize handling turned on), the WM_SIZE handler code
will find a path through the twisty maze of ifs on which the border
between the text and the client-area edges is not recomputed, or
invalidated, or redrawn. So you can end up with half a line of text
from the previous window size still visible at the bottom of the new
window.

Fixed by factoring out the offset-recomputation code from the large
and complicated reset_window(), so that I can call just that snippet
on the dangerous code path.
---
 windows/window.c | 43 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/windows/window.c b/windows/window.c
index ec46e57e..f7e97b8e 100644
--- a/windows/window.c
+++ b/windows/window.c
@@ -1686,6 +1686,25 @@ static void wintw_request_resize(TermWin *tw, int w, int h)
     InvalidateRect(wgs.term_hwnd, NULL, true);
 }
 
+static void recompute_window_offset(void)
+{
+    RECT cr;
+    GetClientRect(wgs.term_hwnd, &cr);
+
+    int win_width  = cr.right - cr.left;
+    int win_height = cr.bottom - cr.top;
+
+    int new_offset_width = (win_width-font_width*term->cols)/2;
+    int new_offset_height = (win_height-font_height*term->rows)/2;
+
+    if (offset_width != new_offset_width ||
+        offset_height != new_offset_height) {
+        offset_width = new_offset_width;
+        offset_height = new_offset_height;
+        InvalidateRect(wgs.term_hwnd, NULL, true);
+    }
+}
+
 static void reset_window(int reinit) {
     /*
      * This function decides how to resize or redraw when the
@@ -1728,12 +1747,8 @@ static void reset_window(int reinit) {
         return;
 
     /* Is the window out of position ? */
-    if ( !reinit &&
-            (offset_width != (win_width-font_width*term->cols)/2 ||
-             offset_height != (win_height-font_height*term->rows)/2) ){
-        offset_width = (win_width-font_width*term->cols)/2;
-        offset_height = (win_height-font_height*term->rows)/2;
-        InvalidateRect(wgs.term_hwnd, NULL, true);
+    if (!reinit) {
+        recompute_window_offset();
 #ifdef RDB_DEBUG_PATCH
         debug("reset_window() -> Reposition terminal\n");
 #endif
@@ -2986,6 +3001,22 @@ static LRESULT CALLBACK WndProc(HWND hwnd, UINT message,
                        (resize_action == RESIZE_EITHER &&
                         !is_alt_pressed())) {
                 wm_size_resize_term(lParam, true);
+
+                /*
+                 * Sometimes, we can get a spontaneous resize event
+                 * outside a WM_SIZING interactive drag which wants to
+                 * set us to a new specific SIZE_RESTORED size. An
+                 * example is what happens if you press Windows+Right
+                 * and then Windows+Up: the first operation fits the
+                 * window to the right-hand half of the screen, and
+                 * the second one changes that for the top right
+                 * quadrant. In that situation, if we've responded
+                 * here by resizing the terminal, we may still need to
+                 * recompute the border around the window and do a
+                 * full redraw to clear the new border.
+                 */
+                if (!resizing)
+                    recompute_window_offset();
             } else {
                 reset_window(0);
             }