Un peu tard, mais pour mémoire.
Vous pouvez obtenir des lignes lisses en utilisant des splines cardinales (aka spline canonique) pour dessiner des courbes lisses passant par les points.
J'ai créé cette fonction pour la toile - elle est divisée en trois fonctions pour augmenter la polyvalence. La fonction principale du wrapper ressemble à ceci:
function drawCurve(ctx, ptsa, tension, isClosed, numOfSegments, showPoints) {
showPoints = showPoints ? showPoints : false;
ctx.beginPath();
drawLines(ctx, getCurvePoints(ptsa, tension, isClosed, numOfSegments));
if (showPoints) {
ctx.stroke();
ctx.beginPath();
for(var i=0;i<ptsa.length-1;i+=2)
ctx.rect(ptsa[i] - 2, ptsa[i+1] - 2, 4, 4);
}
}
Pour dessiner une courbe, utilisez un tableau avec x, y points dans l'ordre: x1,y1, x2,y2, ...xn,yn
.
Utilisez-le comme ceci:
var myPoints = [10,10, 40,30, 100,10]; //minimum two points
var tension = 1;
drawCurve(ctx, myPoints); //default tension=0.5
drawCurve(ctx, myPoints, tension);
La fonction ci-dessus appelle deux sous-fonctions, une pour calculer les points lissés. Cela renvoie un tableau avec de nouveaux points - c'est la fonction principale qui calcule les points lissés:
function getCurvePoints(pts, tension, isClosed, numOfSegments) {
// use input value if provided, or use a default value
tension = (typeof tension != 'undefined') ? tension : 0.5;
isClosed = isClosed ? isClosed : false;
numOfSegments = numOfSegments ? numOfSegments : 16;
var _pts = [], res = [], // clone array
x, y, // our x,y coords
t1x, t2x, t1y, t2y, // tension vectors
c1, c2, c3, c4, // cardinal points
st, t, i; // steps based on num. of segments
// clone array so we don't change the original
//
_pts = pts.slice(0);
// The algorithm require a previous and next point to the actual point array.
// Check if we will draw closed or open curve.
// If closed, copy end points to beginning and first points to end
// If open, duplicate first points to befinning, end points to end
if (isClosed) {
_pts.unshift(pts[pts.length - 1]);
_pts.unshift(pts[pts.length - 2]);
_pts.unshift(pts[pts.length - 1]);
_pts.unshift(pts[pts.length - 2]);
_pts.push(pts[0]);
_pts.push(pts[1]);
}
else {
_pts.unshift(pts[1]); //copy 1. point and insert at beginning
_pts.unshift(pts[0]);
_pts.push(pts[pts.length - 2]); //copy last point and append
_pts.push(pts[pts.length - 1]);
}
// ok, lets start..
// 1. loop goes through point array
// 2. loop goes through each segment between the 2 pts + 1e point before and after
for (i=2; i < (_pts.length - 4); i+=2) {
for (t=0; t <= numOfSegments; t++) {
// calc tension vectors
t1x = (_pts[i+2] - _pts[i-2]) * tension;
t2x = (_pts[i+4] - _pts[i]) * tension;
t1y = (_pts[i+3] - _pts[i-1]) * tension;
t2y = (_pts[i+5] - _pts[i+1]) * tension;
// calc step
st = t / numOfSegments;
// calc cardinals
c1 = 2 * Math.pow(st, 3) - 3 * Math.pow(st, 2) + 1;
c2 = -(2 * Math.pow(st, 3)) + 3 * Math.pow(st, 2);
c3 = Math.pow(st, 3) - 2 * Math.pow(st, 2) + st;
c4 = Math.pow(st, 3) - Math.pow(st, 2);
// calc x and y cords with common control vectors
x = c1 * _pts[i] + c2 * _pts[i+2] + c3 * t1x + c4 * t2x;
y = c1 * _pts[i+1] + c2 * _pts[i+3] + c3 * t1y + c4 * t2y;
//store points in array
res.push(x);
res.push(y);
}
}
return res;
}
Et pour dessiner réellement les points sous forme de courbe lissée (ou toute autre ligne segmentée tant que vous avez un tableau x, y):
function drawLines(ctx, pts) {
ctx.moveTo(pts[0], pts[1]);
for(i=2;i<pts.length-1;i+=2) ctx.lineTo(pts[i], pts[i+1]);
}
var ctx = document.getElementById("c").getContext("2d");
function drawCurve(ctx, ptsa, tension, isClosed, numOfSegments, showPoints) {
ctx.beginPath();
drawLines(ctx, getCurvePoints(ptsa, tension, isClosed, numOfSegments));
if (showPoints) {
ctx.beginPath();
for(var i=0;i<ptsa.length-1;i+=2)
ctx.rect(ptsa[i] - 2, ptsa[i+1] - 2, 4, 4);
}
ctx.stroke();
}
var myPoints = [10,10, 40,30, 100,10, 200, 100, 200, 50, 250, 120]; //minimum two points
var tension = 1;
drawCurve(ctx, myPoints); //default tension=0.5
drawCurve(ctx, myPoints, tension);
function getCurvePoints(pts, tension, isClosed, numOfSegments) {
// use input value if provided, or use a default value
tension = (typeof tension != 'undefined') ? tension : 0.5;
isClosed = isClosed ? isClosed : false;
numOfSegments = numOfSegments ? numOfSegments : 16;
var _pts = [], res = [], // clone array
x, y, // our x,y coords
t1x, t2x, t1y, t2y, // tension vectors
c1, c2, c3, c4, // cardinal points
st, t, i; // steps based on num. of segments
// clone array so we don't change the original
//
_pts = pts.slice(0);
// The algorithm require a previous and next point to the actual point array.
// Check if we will draw closed or open curve.
// If closed, copy end points to beginning and first points to end
// If open, duplicate first points to befinning, end points to end
if (isClosed) {
_pts.unshift(pts[pts.length - 1]);
_pts.unshift(pts[pts.length - 2]);
_pts.unshift(pts[pts.length - 1]);
_pts.unshift(pts[pts.length - 2]);
_pts.push(pts[0]);
_pts.push(pts[1]);
}
else {
_pts.unshift(pts[1]); //copy 1. point and insert at beginning
_pts.unshift(pts[0]);
_pts.push(pts[pts.length - 2]); //copy last point and append
_pts.push(pts[pts.length - 1]);
}
// ok, lets start..
// 1. loop goes through point array
// 2. loop goes through each segment between the 2 pts + 1e point before and after
for (i=2; i < (_pts.length - 4); i+=2) {
for (t=0; t <= numOfSegments; t++) {
// calc tension vectors
t1x = (_pts[i+2] - _pts[i-2]) * tension;
t2x = (_pts[i+4] - _pts[i]) * tension;
t1y = (_pts[i+3] - _pts[i-1]) * tension;
t2y = (_pts[i+5] - _pts[i+1]) * tension;
// calc step
st = t / numOfSegments;
// calc cardinals
c1 = 2 * Math.pow(st, 3) - 3 * Math.pow(st, 2) + 1;
c2 = -(2 * Math.pow(st, 3)) + 3 * Math.pow(st, 2);
c3 = Math.pow(st, 3) - 2 * Math.pow(st, 2) + st;
c4 = Math.pow(st, 3) - Math.pow(st, 2);
// calc x and y cords with common control vectors
x = c1 * _pts[i] + c2 * _pts[i+2] + c3 * t1x + c4 * t2x;
y = c1 * _pts[i+1] + c2 * _pts[i+3] + c3 * t1y + c4 * t2y;
//store points in array
res.push(x);
res.push(y);
}
}
return res;
}
function drawLines(ctx, pts) {
ctx.moveTo(pts[0], pts[1]);
for(i=2;i<pts.length-1;i+=2) ctx.lineTo(pts[i], pts[i+1]);
}
canvas { border: 1px solid red; }
<canvas id="c"><canvas>
Il en résulte ceci:
Vous pouvez facilement étendre le canevas pour pouvoir l'appeler comme ceci à la place:
ctx.drawCurve(myPoints);
Ajoutez ce qui suit au javascript:
if (CanvasRenderingContext2D != 'undefined') {
CanvasRenderingContext2D.prototype.drawCurve =
function(pts, tension, isClosed, numOfSegments, showPoints) {
drawCurve(this, pts, tension, isClosed, numOfSegments, showPoints)}
}
Vous pouvez trouver une version plus optimisée de ceci sur NPM ( npm i cardinal-spline-js
) ou sur GitLab .