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

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

commit 66e7f3b404405cafa2e026be7273b6d280ccf88e
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/NGL 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;
 }