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const X_START = '8*cos(t)';
const Y_START = '8*sin(t)';
const equations = {
x: math.compile(X_START),
y: math.compile(Y_START),
}
window.onload = () => {
const root = document.getElementById('root');
const launchButton = document.createElement('input');
launchButton.type = 'button';
launchButton.value = 'Launch';
const xeq = document.createElement('input');
xeq.value = X_START;
xeq.onchange = (e) => {
equations.x = math.compile(e.target.value);
running = false;
path = computePath(equations, 0, 100, 0.1);
render(ctx, path, 0);
};
xeq.onkeydown = xeq.onchange;
xeq.onkeyup = xeq.onchange;
const yeq = document.createElement('input');
yeq.value = Y_START;
yeq.onchange = (e) => {
equations.y = math.compile(e.target.value);
running = false;
path = computePath(equations, 0, 100, 0.1);
render(ctx, path, 0);
};
yeq.onkeydown = yeq.onchange;
yeq.onkeyup = yeq.onchange;
root.appendChild(xeq);
root.appendChild(yeq);
root.appendChild(launchButton);
const canvas = document.createElement('canvas');
canvas.width = 600;
canvas.height = 600;
root.appendChild(canvas);
const ctx = canvas.getContext('2d');
ctx.translate(canvas.width/2, canvas.height/2)
ctx.scale(canvas.width/20, -canvas.height/20);
let path = computePath(equations, 0, 100, 0.1);
let running = false;
const step = (index) => {
render(ctx, path, index);
if (running && index < path.length-1) {
setTimeout(() => step(index+1), 10);
} else {
running = false;
render(ctx, path, 0);
}
}
launchButton.onclick = () => {
running = false;
setTimeout(() => { running=true; step(0); }, 20);
}
render(ctx, path, 0);
}
function render(ctx, path, index) {
const { width, height } = ctx.canvas;
ctx.fillStyle = 'black';
ctx.fillRect(-width, -height, 2*width, 2*height);
const [x0, y0] = path[index];
const [x1, y1] = path[index+1] || path[index];
const angle = Math.atan2(y1-y0, x1-x0);
drawGrid(ctx);
drawPath(ctx, path);
drawShip(ctx, [x0, y0], angle);
}
function drawShip(ctx, pos, angle) {
const transform = ctx.getTransform();
const { width, height } = ctx.canvas;
const [x, y] = pos;
ctx.translate(x, y);
ctx.rotate(angle);
ctx.fillStyle = 'white';
const STEP = 120/Math.min(width,height);
ctx.beginPath();
ctx.moveTo(0, 0);
ctx.lineTo(-STEP, -STEP);
ctx.lineTo(2*STEP, 0);
ctx.lineTo(-STEP, STEP);
ctx.lineTo(0, 0);
ctx.fill();
ctx.setTransform(transform);
}
function computePath(equations, start, end, step) {
const ts = [...Array(Math.floor((end-start)/step)).keys()].map(k => step * (start+k))
return ts.map(t => [ equations.x.eval({t}), equations.y.eval({t}) ]);
}
function drawGrid(ctx) {
ctx.scale(1, -1);
ctx.strokeStyle = 'white';
ctx.fillStyle = 'white';
const { width, height } = ctx.canvas;
ctx.font = `${200/Math.max(width, height)}px serif`;
ctx.lineWidth = 4 / Math.max(width, height);
const drawLine = (start, end) => {
ctx.beginPath();
ctx.moveTo(start[0], start[1]);
ctx.lineTo(end[0], end[1]);
ctx.stroke();
}
const drawXLabel = (x, y) => {
ctx.textAlign = 'right';
ctx.textBaseline = 'bottom';
ctx.fillText(`${x} `, x, y);
}
const drawYLabel = (x, y) => {
ctx.rotate(Math.PI/2);
ctx.textAlign = 'right';
ctx.textBaseline = 'bottom';
ctx.fillText(`${y} `, y, x);
ctx.rotate(-Math.PI/2);
}
const drawGrid = (start, end, step) => {
[...Array(1+Math.floor((end-start)/step)).keys()].forEach(z => {
z = (step*z)+start;
drawLine([z, start], [z, end]);
drawLine([start, z], [end, z]);
drawXLabel(z, end);
drawYLabel(end, z);
});
}
drawGrid(-10, 10, 2);
ctx.scale(1, -1);
}
function drawPath(ctx, path) {
const [ start, ...line ] = path;
const { width, height } = ctx.canvas;
ctx.strokeStyle = 'white';
ctx.lineWidth = 8 / Math.max(width, height);
ctx.beginPath();
ctx.moveTo(start[0], start[1]);
line.forEach(p => ctx.lineTo(p[0], p[1]));
ctx.stroke();
}
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