Graphic system comprising a fragment graphic module and relative rendering method

A graphic system for rendering an image on a screen of a display unit of a graphic system having a graphic module coupled to and controlled by a central processing unit, comprising:

• a depth test buffer configured to store a current depth value;
• a depth test stage coupled to said depth test buffer and configured to compare the current depth value with a depth value associated with an incoming fragment and to define a resulting fragment;
• a test stage structured to receive the resulting fragment forwarded from the depth test stage and to test the resulting fragment and to generate a retained fragment;
• a further depth test stage configured to perform a further depth test upon disabling of the depth test buffer when testing on a previous fragment having planar coordinates of the incoming fragment is under processing;
• and
• a buffer writing stage configured to update the current depth value with a depth value of the retained fragment.

A fragment graphic pipeline for processing incoming fragments having attributes associated with pixels of an image to be rendered on a display screen, the pipeline comprising:

• a depth/stencil test stage configured to compare a depth value of the incoming fragment with a depth value stored in a depth test buffer, and to further compare planar coordinates in the incoming fragment with test planar coordinates stored in a stencil buffer that define the active area on the display screen to determine if the incoming fragment is included in the active area of the display screen;
• at least a first texturing/blending stage and a last texturing/blending stage coupled to the depth/stencil stage and adapted to apply color attributes to the incoming fragment received from the depth/stencil test stage;
• an alpha test stage coupled to the last texturing/blending stage and adapted to compare a transparency level of the incoming fragment received from the last texturing/blending stage and a reference transparency and to forward down the pipeline the incoming fragment that passes the alpha test stage comparison of the transparency level;
• an additional depth/stencil test stage coupled to the alpha test stage and configured to perform depth and stencil testing of the incoming fragment and to update the depth test buffer and the stencil test buffer;
• and
• a buffer writing stage coupled to the additional depth/stencil test stage to receive the incoming fragment that passes the alpha test stage and adapted to update the depth test buffer to replace the current depth value with a depth value of the incoming fragment that passes the alpha test stage.