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// bbox_intersect.ysl2

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//

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// bounding boxes intersection tests

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// Rates 1D intersection of 2 segments A and B

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// described respectively with a0,a1 and b0,b1

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def "func:intersect_1d" {

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    // it is assumed that a1 > a0 and b1 > b0

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    param "a0";

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    param "a1";

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    param "b0";

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    param "b1";

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    const "d0", "$a0 >= $b0";

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    const "d1", "$a1 >= $b1";

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    choose {

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        when "not($d0) and $d1"

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            // b contained in a

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            //   a0<b0 b1<a1

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            // a +--------+

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            // b    +--+

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            result "3";

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        when "$d0 and not($d1)"

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            // a contained in b

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            //   b0<a0 a1<b1

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            // a    +--+

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            // b +--------+

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            result "2";

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        when "$d0 and $d1 and $a0 < $b1"

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            // a and b are overlapped 

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            //   b0<a0<b1<a1

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            // a    +-----+

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            // b +-----+

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            result "1";

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        when "not($d0) and not($d1) and $b0 < $a1"

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            // a and b are overlapped

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            //   a0<b0<a1<b1

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            // a +-----+

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            // b    +-----+

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            result "1";

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            // since orientation doesn't matter,

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            // rated same as previous symetrical overlapping

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        otherwise

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            result "0"; /* no intersection*/

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}

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// Rates intersection A and B areas described with x,y,w and h 

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// attributes passed as $a and $b parameters.

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// 

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// returns :

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// 0 - no intersection

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//            .-----.

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//    .-----. |    b|

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//    |     | |     |

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//    |     | '-----'

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//    |a    |

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//    '-----'

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//

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// 1 - overlapping

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//        .-----.

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//    .---|--. b|

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//    |   |  |  |

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//    |   '-----'

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//    |a     |

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//    '------'

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//

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// 2 - overlapping

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//        .-----.

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//        |  a  |

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//    .---|-----|---.

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//    |   '-----'   |

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//    | b           |

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//    '-------------'

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//

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// 3 - overlapping

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//        .-----.

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//        |  b  |

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//    .---|-----|---.

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//    |   '-----'   |

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//    | a           |

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//    '-------------'

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//

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// 4 - a contained in b

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//    .-------------.

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//    |   .-----.   |

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//    |   |  a  |   |

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//    |b  '-----'   |

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//    '-------------'

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//

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// 6 - overlapping

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//        .----.

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//        |   b|

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//    .---|----|---.

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//    |a  |    |   |

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//    '---|----|---'

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//        '----'

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//

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// 9 - b contained in a

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//    .-------------.

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//    |   .-----.   |

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//    |   |  b  |   |

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//    |a  '-----'   |

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//    '-------------'

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//

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def "func:intersect" {

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    param "a";

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    param "b";

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    const "x_intersect", "func:intersect_1d($a/@x, $a/@x+$a/@w, $b/@x, $b/@x+$b/@w)";

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    choose{

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        when "$x_intersect != 0"{

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            const "y_intersect", "func:intersect_1d($a/@y, $a/@y+$a/@h, $b/@y, $b/@y+$b/@h)";

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            result "$x_intersect * $y_intersect";

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        otherwise result "0";