wined3d: Add a registry key to disable rendering swapchains onscreen.

dlls/wined3d/swapchain.c

@@ -824,7 +824,8 @@ void swapchain_update_render_to_fbo(struct wined3d_swapchain *swapchain)
             swapchain->presentParms.BackBufferHeight,
             client_rect.right, client_rect.bottom);
 
-    if (swapchain->presentParms.BackBufferWidth == client_rect.right
+    if (!wined3d_settings.always_offscreen
+            && swapchain->presentParms.BackBufferWidth == client_rect.right
             && swapchain->presentParms.BackBufferHeight == client_rect.bottom)
     {
         TRACE("Backbuffer dimensions match window dimensions, rendering onscreen.\n");

dlls/wined3d/wined3d_main.c

@@ -86,6 +86,7 @@ struct wined3d_settings wined3d_settings =
     NULL,           /* No wine logo by default */
     FALSE,          /* Disable multisampling for now due to Nvidia driver bugs which happens for some users */
     FALSE,          /* No strict draw ordering. */
+    FALSE,          /* Try to render onscreen by default. */
 };
 
 /* Do not call while under the GL lock. */
@@ -340,6 +341,12 @@ static BOOL wined3d_dll_init(HINSTANCE hInstDLL)
             TRACE("Enforcing strict draw ordering.\n");
             wined3d_settings.strict_draw_ordering = TRUE;
         }
+        if (!get_config_key(hkey, appkey, "AlwaysOffscreen", buffer, size)
+                && !strcmp(buffer,"enabled"))
+        {
+            TRACE("Always rendering backbuffers offscreen.\n");
+            wined3d_settings.always_offscreen = TRUE;
+        }
     }
     if (wined3d_settings.vs_mode == VS_HW)
         TRACE("Allow HW vertex shaders\n");

dlls/wined3d/wined3d_private.h

@@ -271,6 +271,7 @@ struct wined3d_settings
     char *logo;
     int allow_multisampling;
     BOOL strict_draw_ordering;
+    BOOL always_offscreen;
 };
 
 extern struct wined3d_settings wined3d_settings DECLSPEC_HIDDEN;