Depth, Stencil, & Alpha — The Mesa 3D Graphics Library latest documentation

# Depth, Stencil, & Alpha

These three states control the depth, stencil, and alpha tests, used to discard fragments that have passed through the fragment shader.

Traditionally, these three tests have been clumped together in hardware, so they are all stored in one structure.

During actual execution, the order of operations done on fragments is always:

- Alpha

- Stencil

- Depth

## Depth Members

enabled

  Whether the depth test is enabled.

writemask

  Whether the depth buffer receives depth writes.

func

  The depth test function. One of PIPE_FUNC.

## Stencil Members

enabled

  Whether the stencil test is enabled. For the second stencil, whether the two-sided stencil is enabled. If two-sided stencil is disabled, the other fields for the second array member are not valid.

func

  The stencil test function. One of PIPE_FUNC.

valuemask

  Stencil test value mask; this is ANDed with the value in the stencil buffer and the reference value before doing the stencil comparison test.

writemask

  Stencil test writemask; this controls which bits of the stencil buffer are written.

fail_op

  The operation to carry out if the stencil test fails. One of PIPE_STENCIL_OP.

zfail_op

  The operation to carry out if the stencil test passes but the depth test fails. One of PIPE_STENCIL_OP.

zpass_op

  The operation to carry out if the stencil test and depth test both pass. One of PIPE_STENCIL_OP.

## Alpha Members

enabled

  Whether the alpha test is enabled.

func

  The alpha test function. One of PIPE_FUNC.

ref_value

  Alpha test reference value; used for certain functions.