Method and apparatus for generating compressed stencil test information

1. A method for rendering pixels for display comprising:

generating stencil values on a per pixel basis for storage in stencil buffer memory;

selecting a group of stencil values that represent a block of pixels;

generating per-group compressed stencil data representing the group of stencil values wherein the per-group compressed stencil data is represented as fewer bits than a number of bits that represent the generated stencil value; and

performing stencil testing on a corresponding incoming block of pixels prior to performing rendering using the per-group compressed stencil data.

2. The method of claim 1 wherein generating compressed stencil data includes comparing each of the stencil values in the group to a reference value and based on the comparison, generating the per-group compressed stencil value.

3. An apparatus for rendering pixels for display comprising: circuitry operative to:

generate stencil values on a per pixel basis for storage in stencil buffer memory;

select a group of stencil values that represent a block of pixels;

generate per-group compressed stencil data representing the group of stencil values wherein the compressed stencil data is represented as fewer bits than a number of bits that represent the generated stencil value; and

perform stencil testing on a corresponding incoming block of pixels prior to performing light related rendering using the compressed per-group stencil data.

4. The apparatus of claim 3 wherein when the circuit generates the per-group compressed stencil data by comparing each of the stencil values in the group to reference value and based on the comparison generates the per-group compressed stencil value as represented as fewer bits than the number of bits that represent a generated stencil value.