JavaScript: LERP - Linear Interpolation Function

LERP

First, LERP for reference:

function lerp(a, b, t) {
	return a + (b - a) * t;
}

Or:

function lerp(a, b, t) {
	return a * (1 - t) + b * t;
}

Linear interpolation makes it possible to precisely place a point between, before and after two points.

The heart of the code for the above looks like this.

function lerp(a, b, t) {
	return a * (1 - t) + b * t;
}
var p1 = {x: 50, y: 100};
var p2 = {x: 250, y: 100};
var t = 0.5; // 0.5 == 50% (the default value)
var p3 = {x: lerp(p1.x, p2.x, t), y: 100};

VLERP

Now, this time, easy-in-out with using vector LERP (2 dimensions only).

VLERP for reference:

function vLerp(p1, p2, t) {
	return {
		x: lerp(p1.x, p2.x, t),
		y: lerp(p1.y, p2.y, t)
	};
}

Learn about ease in and out functions at https://easings.net/.

All of the JavaScript code for this page is here:

function lerp(a, b, t) {
	return a + (b - a) * t;
}
function vLerp(p1, p2, t) {
	return {
		x: lerp(p1.x, p2.x, t),
		y: lerp(p1.y, p2.y, t)
	};
}
function drawPoint(ctx, pos, text) {
	ctx.beginPath();
	ctx.fillStyle = "dodgerblue";
	ctx.strokeStyle = "navy";
	ctx.arc(pos.x, pos.y, 20, 0, Math.PI * 2);
	ctx.fill();
	ctx.stroke();
	ctx.fillStyle = "white";
	ctx.textAlign = "center";
	ctx.textBaseline = "middle";
	ctx.font = "bold 13px Courier";
	ctx.fillText(text, pos.x, pos.y);
}
function updateLerpEx(t) {
	if(isNaN(t)) { return; }
	var cvs = document.getElementById("lerp-canvas");
	var ctx = cvs.getContext("2d");
	ctx.clearRect(0, 0, cvs.width, cvs.height);
	var i = {x: 50, y: 100};
	var j = {x: 250, y: 100};
	drawPoint(ctx, i, "i");
	drawPoint(ctx, j, "j");
	drawPoint(ctx, {x: lerp(i.x, j.x, t), y: 100}, t);
}
updateLerpEx(0.5);
function animateEase() {
	var cvs = document.getElementById("vlerp-canvas");
	var ctx = cvs.getContext("2d");
	ctx.clearRect(0, 0, cvs.width, cvs.height);
	var i = {x: 30, y: 30};
	var j = {x: 270, y: 270};
	var t = (Math.sin(new Date().getTime() / 1000) + 1) * 0.5;
	var c = vLerp(i, j, t)
	drawPoint(ctx, i, "i");
	drawPoint(ctx, j, "j");
	drawPoint(ctx, c, Math.round(t * 10) / 10);
	requestAnimationFrame(animateEase);
}
animateEase();

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