patch 7.4.869

Problem:    MS-Windows: scrolling may cause text to disappear when using an
            Intel GPU.
Solution:   Call GetPixel(). (Yohei Endo)

src/gui_w48.c

@@ -2996,6 +2996,20 @@ get_scroll_flags(void)
     return 0;
 }
 
+/*
+ * On some Intel GPUs, the regions drawn just prior to ScrollWindowEx()
+ * may not be scrolled out properly.
+ * For gVim, when _OnScroll() is repeated, the character at the
+ * previous cursor position may be left drawn after scroll.
+ * The problem can be avoided by calling GetPixel() to get a pixel in
+ * the region before ScrollWindowEx().
+ */
+    static void
+intel_gpu_workaround(void)
+{
+    GetPixel(s_hdc, FILL_X(gui.col), FILL_Y(gui.row));
+}
+
 /*
  * Delete the given number of lines from the given row, scrolling up any
  * text further down within the scroll region.
@@ -3007,6 +3021,8 @@ gui_mch_delete_lines(
 {
     RECT	rc;
 
+    intel_gpu_workaround();
+
     rc.left = FILL_X(gui.scroll_region_left);
     rc.right = FILL_X(gui.scroll_region_right + 1);
     rc.top = FILL_Y(row);
@@ -3038,6 +3054,8 @@ gui_mch_insert_lines(
 {
     RECT	rc;
 
+    intel_gpu_workaround();
+
     rc.left = FILL_X(gui.scroll_region_left);
     rc.right = FILL_X(gui.scroll_region_right + 1);
     rc.top = FILL_Y(row);

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    869,
 /**/
     868,
 /**/