test-canvas/spline.js

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JavaScript
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import { resizeCanvas, drawCircle, drawLine, cubicBezier, quadraticBezier } from "./common.js"
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function drawPoints(ctx, points) {
for (const p of points) {
drawCircle(ctx, p, 2, 0xFF00FF);
}
}
function drawCurve(ctx, curve) {
for (let i=0; i < curve.length - 1; ++i) {
drawLine(ctx, curve[i], curve[i+1], 0xFFFFFF);
}
}
function draw(ctx, points) {
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let start = 0;
while (true) {
const sl = points.slice(start, start + 4);
if (sl.length === 4) {
const bezier = cubicBezier(...sl);
drawCurve(ctx, bezier);
start += 3;
} else if (sl.length === 3) {
const bezier = quadraticBezier(...sl);
drawCurve(ctx, bezier);
start += 2;
} else {
break;
}
}
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drawPoints(ctx, points);
}
function init() {
const canvas = document.getElementById("canvas");
let selection = undefined;
let points = [
{ x: 227, y: 434 },
{ x: 341, y: 234 },
{ x: 649, y: 255 },
{ x: 765, y: 450 },
{ x: 800, y: 500 },
{ x: 850, y: 450 },
{ x: 900, y: 550 },
];
if (canvas.getContext) {
const ctx = canvas.getContext("2d");
resizeCanvas(ctx); // Init canvas
draw(ctx, points);
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canvas.oncontextmenu = (evt) => {
evt.preventDefault();
points = [];
// redraw
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
draw(ctx, points);
};
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canvas.onmousedown = (evt) => {
const { clientX, clientY } = evt;
for (const p of points) {
if (Math.abs(p.x - clientX) < 10 && Math.abs(p.y - clientY) < 10) {
selection = points.indexOf(p);
}
}
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if (selection === undefined) {
points.push({ x: clientX, y: clientY });
// redraw
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
draw(ctx, points);
}
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};
canvas.onmousemove = (evt) => {
if (selection !== undefined) {
points[selection].x = evt.clientX;
points[selection].y = evt.clientY;
// redraw
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
draw(ctx, points);
}
};
canvas.onmouseup = () => {
selection = undefined;
};
}
}
init();