Public
Edited
Oct 25, 2020
3 forks
10 stars
// Intersection of circle: x² + (y - cy)² = radius² and line: y = line_y,
// i.e. solutions to x² + (line_y - cy)² = radius²
px = Math.sqrt(radius**2 - (line_y - cy)**2)
{
const ct = canvas.ct;
ct.clearRect(0, 0, WIDTH, HEIGHT);
// First draw the focus …
ct.beginPath();
ct.arc(cx, cy, 5, 0, 7);
ct.fillStyle = "blue";
ct.fill();
// … and directrix
ct.beginPath();
ct.moveTo(0, HEIGHT - DIRECTRIX_Y);
ct.lineTo(WIDTH, HEIGHT - DIRECTRIX_Y);
ct.lineWidth = 1;
ct.strokeStyle = "blue";
ct.stroke();
// Now draw the dynamic circle and line
ct.beginPath();
// the circle
ct.arc(cx, cy, radius, 0, 7);
// the line
ct.moveTo(0, line_y);
ct.lineTo(WIDTH, line_y);
ct.strokeStyle = "#666";
ct.lineWidth = 1;
ct.stroke();
if (!isNaN(px)) {
// Draw the resulting parabola
ct.beginPath();
ct.moveTo(cx - px, line_y);
ct.quadraticCurveTo(cx, (HEIGHT - DIRECTRIX_Y) + cy - line_y, cx + px, line_y);
ct.lineWidth = 3;
ct.strokeStyle = "red";
ct.stroke();
// Mark the points of intersection
ct.beginPath();
ct.arc(cx - px, line_y, 4, 0, 7);
ct.arc(cx + px, line_y, 4, 0, 7);
ct.fillStyle = "#000";
ct.fill();
}
return this || html`(<i>the drawing function</i>)`;
}
One platform to build and deploy the best data apps
Experiment and prototype by building visualizations in live JavaScript notebooks. Collaborate with your team and decide which concepts to build out.
Use Observable Framework to build data apps locally. Use data loaders to build in any language or library, including Python, SQL, and R.
Seamlessly deploy to Observable. Test before you ship, use automatic deploy-on-commit, and ensure your projects are always up-to-date.