# The CairoOperator class

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## Introduction

This is used to set the compositing operator for all cairo drawing operations.

The default operator is `CairoOperator::OVER`

The operators marked as unbounded modify their destination even outside of the mask layer (that is, their effect is not bound by the mask layer). However, their effect can still be limited by way of clipping.

To keep things simple, the operator descriptions here document the behavior for when both source and destination are either fully transparent or fully opaque. The actual implementation works for translucent layers too. For a more detailed explanation of the effects of each operator, including the mathematical definitions, see http://cairographics.org/operators/.

## Class synopsis

CairoOperator {
/* Constants */
const integer CLEAR = 0 ;
const integer SOURCE = 1 ;
const integer OVER = 2 ;
const integer IN = 3 ;
const integer OUT = 4 ;
const integer ATOP = 5 ;
const integer DEST = 6 ;
const integer DEST_OVER = 7 ;
const integer DEST_IN = 8 ;
const integer DEST_OUT = 9 ;
const integer DEST_ATOP = 10 ;
const integer XOR = 11 ;
const integer ADD = 12 ;
const integer SATURATE = 13 ;
}

## Predefined Constants

`CairoOperator::CLEAR`

  Clear destination layer (bounded)

`CairoOperator::SOURCE`

  Replace destination layer (bounded)

`CairoOperator::OVER`

  Draw source layer on top of destination layer (bounded)

`CairoOperator::IN`

  Draw source where there was destination content (unbounded)

`CairoOperator::OUT`

  Draw source where there was no destination content (unbounded)

`CairoOperator::ATOP`

  Draw source on top of destination content and only there

`CairoOperator::DEST`

  Ignore the source

`CairoOperator::DEST_OVER`

  Draw destination on top of source

`CairoOperator::DEST_IN`

  Leave destination only where there was source content (unbounded)

`CairoOperator::DEST_OUT`

  Leave destination only where there was no source content

`CairoOperator::DEST_ATOP`

  Leave destination on top of source content and only there (unbounded)

`CairoOperator::XOR`

  Source and destination are shown where there is only one of them

`CairoOperator::ADD`

  Source and destination layers are accumulated

`CairoOperator::SATURATE`

  Like `CairoOperator::OVER`, but assuming source and dest are disjoint geometries