Rotate a line around a circle
I have two arcs with strokes and I want an animated line between them. The animation of the line should be perpendicular to the points of the inner circle.
This is what I want, almost what I want.
The problem is:
- The length of the wire is not the length between the 2 turns because it rotates around the inner turn.
- Sometimes the line is not perpendicular to the point of the inner circle. For example, when it gets to the rounded corners, it's tilted a little bit.
I'm having trouble understanding how to use the trig function lineTo. Probably because that changes the length of the line and I don't know how to get the x and y coordinates of the outer circle to get the end point of the line. I'm used to it math.cos * lengthand this gives me a slash. I have nothing, I just want the coordinates of the outer circle.
window.onload = function(){
var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");
function lineAtAngle(startX, startY, angleDeg, length, startX2, startY2, angleDeg2, length2){
var angle = angleDeg * (Math.PI / 180);
var angle2 = angleDeg2 * (Math.PI / 180);
// context.moveTo(startX, startY);
context.beginPath();
context.moveTo(
Math.cos(angle) * length + startX,
Math.sin(angle) * length + startY
)
context.lineTo(
Math.cos(angle2) *(length2 )+ startX2,
Math.sin(angle2) *(length2) + startY2
)
// context.lineTo(canvas.width / 2 + 60, canvas.height / 2, angle2, length2)
context.lineWidth = 10;
context.stroke();
context.closePath();
console.log("startX2: " + startX2 + " startY2: " + startY2 )
console.log(Math.sin(angle2) + startY2)
console.log(length)
}
function myLineTo(startX, startY, angleDeg, length){
}
var length1 = canvas.width / 2 + 60 - canvas.width / 2 -30
var length2 = canvas.width / 2 ;
// var length2 = 1;
console.log(length2)
var angle1 = 0;
var angle2 = 0;
(function animate(){
context.clearRect(0,0, canvas.width, canvas.height);
window.requestAnimationFrame(animate);
context.beginPath()
context.arc(canvas.width / 2, canvas.height / 2, 30, 0, 2 * Math.PI, true)
context.lineWidth = 1;
context.stroke()
context.beginPath();
context.arc(canvas.width / 2, canvas.height / 2, 60, 0, 2 * Math.PI, true);
context.stroke();
context.closePath()
context.beginPath();
context.arc(canvas.width / 2, canvas.height / 2, 3, 0, 2 * Math.PI, true)
context.fill()
context.closePath();
angle1++
angle2++
// lineAtAngle(canvas.width / 2 , canvas.height / 2 , angle1, length1, canvas.width / 2 + 60, canvas.height / 2, angle2, length2 )
lineAtAngle(canvas.width / 2 , canvas.height / 2 , angle1, length1, canvas.width / 2 + 60, canvas.height / 2, angle2, length2 )
}())
} canvas{
background: #aaa;
}<canvas id="canvas" width="400" height="400"></canvas>The idea of drawing a line is that you need to provide a start point ( moveTo) and an end point ( lineTo). Your current code complicates the whole thing with multiple angles and lengths. You want to imagine that what you are doing is starting from the center of the circle and adding an offset to place the starting point on the edge of the inner circle. Using trig here is great. The length of the line will simply be the outer radius minus the inner radius, which is the same direction as the offset (only one angle is needed).
Without fundamentally changing your approach, the code below shows the changes you can use to try this out. Let the linefunction take a start point (x,y) and offset and angle and length. The starting point is the center of the circle, and the offset is the radius of the inner circle. The length (again) is the outer radius minus the inner radius.
window.onload = function(){
var innerCircleRadius = 30;
var outerCircleRadius = 60;
var canvas = document.getElementById("canvas");
var context = canvas.getContext("2d");
var angle1 = 0;
function lineAtAngle(startX, startY, angleDeg, offset, length) {
var angle = angleDeg * (Math.PI / 180); // Convert to radians.
var cosAngle = Math.cos(angle); // Only need cos(angle) once.
var sinAngle = Math.sin(angle); // Only need sin(angle) once.
var startXPos = cosAngle * offset + startX;
var startYPos = sinAngle * offset + startY;
var endXPos = cosAngle * length + startXPos;
var endYPos = sinAngle * length + startYPos;
context.beginPath();
context.moveTo(startXPos, startYPos);
context.lineTo(endXPos, endYPos);
context.lineWidth = 10;
context.stroke();
context.closePath();
}
(function animate() {
context.clearRect(0,0, canvas.width, canvas.height);
window.requestAnimationFrame(animate);
context.beginPath()
context.arc(canvas.width / 2, canvas.height / 2, innerCircleRadius, 0, 2 * Math.PI, true)
context.lineWidth = 1;
context.stroke()
context.beginPath();
context.arc(canvas.width / 2, canvas.height / 2, outerCircleRadius, 0, 2 * Math.PI, true);
context.stroke();
context.closePath()
context.beginPath();
context.arc(canvas.width / 2, canvas.height / 2, 3, 0, 2 * Math.PI, true)
context.fill()
context.closePath();
angle1++
lineAtAngle(canvas.width / 2 , canvas.height / 2 , angle1, innerCircleRadius, outerCircleRadius - innerCircleRadius);
}())
}canvas {
background: #aaa;
}<canvas id="canvas" width="400" height="400"></canvas>