Graphics.GL.Low.Stencil

Documentation

The stencil test is like a configurable depth test with a dedicated additional buffer. Like the depth test, if the stencil test fails then the pixel being tested will not be rendered. The stencil test happens before the depth test, if it's enabled. For a given pixel, the stencil test passes if the following computation

(ref & mask) `stencilOp` (buf & mask)

computes true. The variables ref and mask are configurable constants, buf is the value in the stencil buffer at the given pixel, and stencilOp is a configurable comparison operation. The stencil op can also be set to pass Always or Never.

The stencil buffer may be modified in various ways on the following events:

• When the stencil test fails or
• When the stencil test passes then the depth test fails or
• When both tests pass.

enableStencil :: Stencil -> IO ()

Enable the stencil test with a set of operating parameters.

disableStencil :: IO ()

Disable the stencil test and updates to the stencil buffer, if one exists.

clearStencilBuffer :: IO ()

Clear the stencil buffer with all zeros.

basicStencil :: Stencil

In this basic configuration of the stencil, anything rendered will create a silhouette of 1s in the stencil buffer. Attempting to render a second time into the silhouette will have no effect because the stencil test will fail (ref=1 isn't greater than buffer=1).

def { func = Greater
    , ref = 1
    , onBothPass = Replace }

data Stencil

Configuration of the stencil test and associated stencil buffer updating.

Constructors

Stencil

Fields

func :: StencilFunc

ref :: Int

mask :: Word

onStencilFail :: StencilOp

onDepthFail :: StencilOp

onBothPass :: StencilOp

Instances

Default Stencil

The default state of the stencil, if it were simply enabled, would be to always pass and update nothing in the buffer. It would have no effect on rendering.

data StencilFunc

The stencil test passes under what condition.

Constructors

Never

Less

LessOrEqual

Greater

GreaterOrEqual

Equal

NotEqual

Always

Instances

Show StencilFunc

ToGL StencilFunc

data StencilOp

Modification action for the stencil buffer.

Constructors

Keep

Do nothing.

Zero

Set to zero.

Replace

Write the ref value passed to enableStencil.

Increment

Decrement

Invert

Bitwise complement.

IncrementWrap

DecrementWrap

Instances

Show StencilOp

ToGL StencilOp