Ability to create local RenderingDevice instances.

servers/rendering/rendering_device.cpp

@@ -60,5 +60,7 @@ Vector<uint8_t> RenderingDevice::shader_compile_from_source(ShaderStage p_stage,
 }
 
 RenderingDevice::RenderingDevice() {
-	singleton = this;
+	if (singleton == nullptr) { // there may be more rendering devices later
+		singleton = this;
+	}
 }

servers/rendering/rendering_device.h

@@ -1024,6 +1024,11 @@ public:
 
 	virtual uint32_t get_frame_delay() const = 0;
 
+	virtual void submit() = 0;
+	virtual void sync() = 0;
+
+	virtual RenderingDevice *create_local_device() = 0;
+
 	static RenderingDevice *get_singleton();
 	RenderingDevice();
 };