JavaScript: distance and angle between two points

[Jason Knight]

It's actually funny how much this comes up when people message me directly for help. Usually it's for between a fixed point in the document or in the canvas and the mouse.

You know that geometry and trigonometry you always thought would be useless in high school? Yeah, that.

Code: [Select]

function vectorBetween(point1, point2) {
var
result = {
distanceX = point2.x - point1.x,
distanceY = point2.y - point1.y
};
result.distance = Math.sqrt(
result.distanceX * result.distanceX +
result.distanceY * result.distanceY
);
result.angle = Math.atan2(result.distanceX, result.distanceY);
return result;
}

Assuming your "points" are an object of { x, y }. YES, I know that technically the points are vectors, but "normal" people know them as points so I wrote it for the normies, not those of us who know how to use the terminology correctly... because the correct terminology scares the straights.

Oh and the angle is in radians, since that's what's useful for Math.sin and Math.cos. If you need it in degrees, add a line before the return reading:

Code: [Select]

result.degrees = result.angle * 180 / Math.PI;

Arctangents are your friend.

I actually use them in OpenGL / Vulcan programming for manual projections rather than dividing by "z". You lose hardware projection handling, but gain a lot more control over FOV -- to the point you can do a 360 degree projection with ease to any render target. "The ultimate fisheye".