A graphic system having a central processing unit; a system memory coupled to the central processing unit; a display unit provided with a corresponding screen; a graphic module coupled to and controlled by the central processing unit to render an image on the screen of the display unit, the graphic module including a fragment graphic module having a depth test buffer for storing a current depth value; a depth test stage coupled to the depth test buffer for comparing the current depth value with a depth coordinate associated with an incoming fragment and defining a resulting fragment; a test stage for testing the resulting fragment and defining a retained fragment; a buffer writing stage operatively associated with the test stage for receiving the retained fragment, the buffer writing stage coupled to the depth test buffer for updating the current depth value with a depth value of the retained fragment.