canvas - How find if a point is in a wedge of a other point javascript -


i have canvas , draw 2 points. have draw 2 straight lines each point. must check whether point u sees point v , vice versa.

to know, necessary see if point v in wedge of point u , vice versa:

-here v wedge of u, v sees u u don't see v

-here v sees u , u sees v

if 2 points in wedge of each 1 segment drawn between 2 points.

how can kind of wedge in canvas javascript?

cross product of 2 vectors.

using cross product of line (x1,y1, x2,y2) ax vector (x2-x1, y2-y1) , vector line start point x,y (x - x1, y - y1) give number negative if point left of line, 0 if point along line, , positive if point right of line.

thus point in view of v has to right of v's left arm , left of v's right arm.

a v described follows

const v = {     lx : ?,  // point on left v     ly : ?,      x : ?,  // point of v     y : ?,     rx : ?,     ry : ?, }

the following function return true if v1 can see v2 v1 , v2 objects described above.

function cansee(v1,v2){     const lx = v1.lx - v1.x;  // vector center left line end     const ly = v1.ly - v1.y;     const cx = v2.x  - v1.x;  // vector center v2's center     const cy = v2.y  - v1.y;     const rx = v1.rx - v1.x;  // vector center right line end     const ry = v1.ry - v1.y;      // cross product of left , right arms other v's center     const lc = lx * cy - ly * cx;     const rc = rx * cy - ry * cx;      return (lc > 0 && rc < 0);  // return true if v2 center right of                                 // left arm , left of arm.                                 // else return false; }

using function can find out if both can see each other follows.

if(cansee(v1, v2) && cansee(v2, v1)){ } // both can see each other else { } //one or none can see other

it important points on correct sides. left , right defined when standing @ line start , looking towards line end


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