Ray-casting algorithm: Difference between revisions

=={{header|Factor}}==

To test whether a ray intersects a line, we test that the starting point is between the endpoints in y value, and that it is to the left of the point on the segment with the same y value. Note that this implementation does not support polygons with horizontal edges.

<lang factor>USING: kernel prettyprint sequences arrays math math.vectors ;

IN: raycasting

: between ( a b x -- ? ) [ last ] tri@ [ < ] curry bi@ xor ;

: lincomb ( a b x -- w )

3dup [ last ] tri@

[ - ] curry bi@

[ drop ] 2dip

neg 2dup + [ / ] curry bi@

[ [ v*n ] curry ] bi@ bi* v+ ;

: leftof ( a b x -- ? ) dup [ lincomb ] dip [ first ] bi@ > ;

: ray ( a b x -- ? ) [ between ] [ leftof ] 3bi and ;

: raycast ( poly x -- ? )

[ dup first suffix [ rest-slice ] [ but-last-slice ] bi ] dip

[ ray ] curry 2map

f [ xor ] reduce ;</lang>

Usage:

<lang factor>( scratchpad ) CONSTANT: square { { -2 -1 } { 1 -2 } { 2 1 } { -1 2 } }

( scratchpad ) square { 0 0 } raycast .

t

( scratchpad ) square { 5 5 } raycast .

f

( scratchpad ) square { 2 0 } raycast .

f</lang>