Apparatus and method of an improved stencil shadow volume operation

A system comprising:

• a first stencil buffer configured to perform a stencil shadow volume operation on a group of pixels, wherein the group of pixels comprises a tile;
• w herein the first stencil buffer is further configured to perform a stencil operation on a pixel wherein the pixel is in the group of pixels;
• a graphics processing unit configured to generate a shadow effect, wherein the shadow effect is generated with a stencil shadow volume operation;
• logic within the graphics processing unit configured to store a tile stencil record in the first stencil buffer;
• and
• a first stencil buffer cache;
• wherein the first stencil buffer cache is configured to communicate with the first stencil buffer.

A method for implementing a stencil shadow volume method in a computer graphics system, comprising:

• generating a tile stencil shadow record,
• generating a pixel stencil shadow record;
• generating a tile depth value record;
• and
• performing a stencil shadow volume operation, wherein the stencil shadow volume operation is configured to utilizing the tile stencil shadow record, wherein the stencil shadow volume operation is further configured to utilize the pixel stencil shadow record.

A system, comprising:

• means for performing a stencil shadow volume operation on a plurality of groups of pixels;
• wherein one of the plurality of groups of pixels comprises a first group of pixels, where the first group of pixels comprises a first number of pixels;
• wherein one of the plurality of groups of pixels comprises a second group of pixels, where the second group of pixels comprises a second number of pixels;
• wherein the first number of pixels is greater than the second number of pixels.

A method of rendering shadows in a computer graphics system, comprising:

• evaluating a subtile for compression, the subtile associated with a compressed z-data buffer;
• selectively flushing the subtile to a pixel z-data/stencil buffer, wherein the flushed subtile does not compress in a compressed stencil buffer;
• and
• performing the stencil shadow volume operation in a compressed stencil buffer.

In a computer graphics system, a method of merging compressed stencil data into a pixel stencil buffer in a stencil shadow volume pass, the method comprising:

• testing a subtile for a first condition and a second condition, wherein the first condition comprises subtile underflow, wherein the second condition comprises subtile overflow, and wherein if either the first condition or the second condition is true a subtile status is changed from accept to retest;
• setting a subtile merge mask, for identifying compressed stencil data in a compressed stencil buffer to flush into a pixel stencil buffer;
• merging the compressed stencil data into the pixel stencil buffer, such that a resultant value is the sum of the compressed stencil data and stencil data in the pixel stencil buffer;
• resetting a subtile dirty bit in the compressed stencil buffer, wherein the reset value is zero;
• and
• clearing the compressed stencil value in the compressed stencil buffer.

In a computer graphics system, a method of merging compressed stencil data into a pixel stencil buffer in a specular color pass, the method comprising:

• reading a tile dirty bit in a compressed stencil data record, wherein if the tile dirty bit is zero then a merge operation is not performed;
• reading a subtile dirty bit in the compressed stencil data record, wherein if the subtile dirty bit is zero then the merge operation is not performed;
• setting a subtile merge mask, for identifying compressed stencil data in a compressed stencil buffer to flush into a pixel stencil buffer;
• merging the compressed stencil data and pixel stencil data;
• and
• writing the sum of the compressed stencil data and pixel stencil data into the pixel stencil buffer.