Calculate 2D rotation javascript HTML canvas
Solution 1:
Here is how I would do it:
function getRectangeCoordinates(x, y, width, height, angle) {
let points = [ [x, y] ]
let radians = (Math.PI / 180) * angle;
for (let i = 0; i < 3; i++) {
x += Math.cos(radians) * ((i == 1) ? height : width);
y += Math.sin(radians) * ((i == 1) ? height : width);
points.push([x, y])
radians += Math.PI / 2
}
return points
}
let canvas = document.createElement("canvas");
canvas.width = canvas.height = 140
let ctx = canvas.getContext('2d');
document.body.appendChild(canvas);
function draw(coords, radius) {
for (let i = 0; i < 4; i++) {
ctx.beginPath();
ctx.arc(coords[i][0], coords[i][1], radius, 0, 8);
ctx.moveTo(coords[i][0], coords[i][1]);
let next = (i + 1) % 4
ctx.lineTo(coords[next][0], coords[next][1]);
ctx.stroke();
}
}
let coords = getRectangeCoordinates(20, 10, 120, 40, 15)
console.log(JSON.stringify(coords))
draw(coords, 3)
ctx.strokeStyle = "red";
coords = getRectangeCoordinates(60, 40, 40, 50, 65)
draw(coords, 5)
ctx.strokeStyle = "blue";
coords = getRectangeCoordinates(120, 3, 20, 20, 45)
draw(coords, 2)In the getRectangeCoordinates I'm returning all corners of a rectangle and the paraments of the function are the top left corner (x, y) the height and width of the rectangle and last the angle.
I'm drawing a few rectangles with different shapes and angles to show how it looks like
The calculations in the function are simple trigonometry here is a visual representation that could help you remember it the next time you need it:
