Revert "cogl: Drop Rendererer.set_driver"

This reverts commit 6c22b7faba8112065a611921a538b9f66d9500bf.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4312>

cogl/cogl/cogl-renderer-private.h

@@ -47,6 +47,7 @@ struct _CoglRenderer
   CoglDisplay *display;
 
   gboolean connected;
+  CoglDriverId driver_override;
   CoglDriver *driver;
   CoglTextureDriver *texture_driver;
   const CoglWinsysVtable *winsys_vtable;

cogl/cogl/cogl-renderer.c

@@ -277,6 +277,21 @@ _cogl_renderer_choose_driver (CoglRenderer *renderer,
         invalid_override = driver_name;
     }
 
+  if (renderer->driver_override != COGL_DRIVER_ID_ANY)
+    {
+      if (driver_override != COGL_DRIVER_ID_ANY &&
+          renderer->driver_override != driver_override)
+        {
+          g_set_error (error, COGL_RENDERER_ERROR,
+                       COGL_RENDERER_ERROR_BAD_CONSTRAINT,
+                       "Application driver selection conflicts with driver "
+                       "specified in configuration");
+          return FALSE;
+        }
+
+      driver_override = renderer->driver_override;
+    }
+
   if (driver_override != COGL_DRIVER_ID_ANY)
     {
       gboolean found = FALSE;
@@ -536,6 +551,14 @@ cogl_renderer_get_proc_address (CoglRenderer *renderer,
   return winsys->renderer_get_proc_address (renderer, name);
 }
 
+void
+cogl_renderer_set_driver (CoglRenderer *renderer,
+                          CoglDriverId  driver)
+{
+  g_return_if_fail (!renderer->connected);
+  renderer->driver_override = driver;
+}
+
 CoglDriverId
 cogl_renderer_get_driver_id (CoglRenderer *renderer)
 {

cogl/cogl/cogl-renderer.h

@@ -196,6 +196,24 @@ typedef enum
   COGL_DRIVER_ID_GLES2,
 } CoglDriverId;
 
+/**
+ * cogl_renderer_set_driver:
+ * @renderer: An unconnected #CoglRenderer
+ *
+ * Requests that Cogl should try to use a specific underlying driver
+ * for rendering.
+ *
+ * If you select an unsupported driver then cogl_renderer_connect()
+ * will fail and report an error. Most applications should not
+ * explicitly select a driver and should rely on Cogl automatically
+ * choosing the driver.
+ *
+ * This may only be called on an un-connected #CoglRenderer.
+ */
+COGL_EXPORT void
+cogl_renderer_set_driver (CoglRenderer *renderer,
+                          CoglDriverId  driver);
+
 /**
  * cogl_renderer_get_driver_id:
  * @renderer: A connected #CoglRenderer