[gtk/mesa.win32-4.0] gdkglcontext-win32.c: Fix running with Mesa drivers

[Chun-wei Fan <fanchunwei src gnome org>]

commit a16aa7d4a4c34bcecf780852d17735f1ba82d51b
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Thu Apr 29 12:04:42 2021 +0800

    gdkglcontext-win32.c: Fix running with Mesa drivers
    
    Some GL drivers such as Mesa-D3D12 do not allow one to call SetPixelFormat() on
    a given HDC if one pixel format has been already set for it, so first check the
    HDC with GetPixelFormat() to see whether a pixel format has already been set
    with the HDC, and only attempt to acquire the pixel format if one has not been
    set.
    
    This will fix running with GL on Windows using the Mesa drivers.

 gdk/win32/gdkglcontext-win32.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)
---
diff --git a/gdk/win32/gdkglcontext-win32.c b/gdk/win32/gdkglcontext-win32.c
index c7e7fa3345..610711d3b8 100644
--- a/gdk/win32/gdkglcontext-win32.c
+++ b/gdk/win32/gdkglcontext-win32.c
@@ -712,20 +712,30 @@ _set_pixformat_for_hdc (HDC              hdc,
                         int             *best_idx,
                         GdkWin32Display *display)
 {
-  PIXELFORMATDESCRIPTOR pfd;
-  gboolean set_pixel_format_result = FALSE;
+  gboolean already_checked = TRUE;
+  *best_idx = GetPixelFormat (hdc);
 
   /* one is only allowed to call SetPixelFormat(), and so ChoosePixelFormat()
    * one single time per window HDC
    */
-  *best_idx = _get_wgl_pfd (hdc, &pfd, display);
+  if (*best_idx == 0)
+    {
+      PIXELFORMATDESCRIPTOR pfd;
+      gboolean set_pixel_format_result = FALSE;
 
-  if (*best_idx != 0)
-    set_pixel_format_result = SetPixelFormat (hdc, *best_idx, &pfd);
+      GDK_NOTE (OPENGL, g_print ("requesting pixel format...\n"));
+         already_checked = FALSE;
+      *best_idx = _get_wgl_pfd (hdc, &pfd, display);
 
-  /* ChoosePixelFormat() or SetPixelFormat() failed, bail out */
-  if (*best_idx == 0 || !set_pixel_format_result)
-    return FALSE;
+      if (*best_idx != 0)
+        set_pixel_format_result = SetPixelFormat (hdc, *best_idx, &pfd);
+
+      /* ChoosePixelFormat() or SetPixelFormat() failed, bail out */
+      if (*best_idx == 0 || !set_pixel_format_result)
+        return FALSE;
+    }
+
+  GDK_NOTE (OPENGL, g_print ("%s""requested and set pixel format: %d\n", already_checked ? "already " : "", 
*best_idx));
 
   return TRUE;
 }