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.