Commit: patch 9.2.0858: MS-Windows GUI: white flash when VimEnter is slow

patch 9.2.0858: MS-Windows GUI: white flash when VimEnter is slow

Commit: https://github.com/vim/vim/commit/70da6c1a995601042a88f059523a3c95f31d39ac
Author: Hirohito Higashi <[email protected]>
Date:   Sun Jul 26 14:56:09 2026 +0000

    patch 9.2.0858: MS-Windows GUI: white flash when VimEnter is slow
    
    Problem:  In the MS-Windows GUI the window is shown before the screen is
              drawn for the first time.  Until then it displays undefined
              content, which appears as a white flash when a VimEnter
              autocommand delays the first redraw.
    Solution: Use the background color for the window as long as the screen
              contents are not available, and paint it again when the
              background color changes while only that color is shown.
    
    fixes:  #20757
    closes: #20807
    
    Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
    Signed-off-by: Hirohito Higashi <[email protected]>
    Signed-off-by: Christian Brabandt <[email protected]>

diff --git a/src/gui_w32.c b/src/gui_w32.c
index d9dbe65ac..7e6c87ee2 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -379,6 +379,11 @@ static WPARAM		s_wParam = 0;
 static LPARAM		s_lParam = 0;
 
 static HWND		s_textArea = NULL;
+
+// Set when the text area was painted with the background color only, because
+// the screen contents were not available yet.
+static bool		s_textarea_bg_only = false;
+
 static UINT		s_uMsg = 0;
 
 static char_u		*s_textfield; // Used by dialogs to pass back strings
@@ -1632,6 +1637,10 @@ gui_mch_new_colors(void)
     prevBrush = (HBRUSH)SetClassLongPtr(
 				s_hwnd, GCLP_HBRBACKGROUND, (LONG_PTR)s_brush);
     InvalidateRect(s_hwnd, NULL, TRUE);
+    // The text area is a child window, the invalidation above does not
+    // include it.
+    if (s_textarea_bg_only && s_textArea != NULL)
+	InvalidateRect(s_textArea, NULL, TRUE);
     DeleteObject(prevBrush);
 }
 
@@ -3714,6 +3723,15 @@ _OnPaint(
 
     if (!IsRectEmpty(&ps.rcPaint))
     {
+	// The text area has no background brush, thus undefined pixels remain
+	// visible until the screen contents are drawn.
+	if (!screen_cleared || ScreenLines == NULL)
+	{
+	    clear_rect(&ps.rcPaint);
+	    s_textarea_bg_only = true;
+	}
+	else
+	    s_textarea_bg_only = false;
 	gui_redraw(ps.rcPaint.left, ps.rcPaint.top,
 		ps.rcPaint.right - ps.rcPaint.left + 1,
 		ps.rcPaint.bottom - ps.rcPaint.top + 1);
diff --git a/src/version.c b/src/version.c
index ba72d4ad8..8dcb28fb0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    858,
 /**/
     857,
 /**/

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