create multiple draggable circles in canvas

Question

I\'m having trouble with making several circles in a HTML canvas draggable. I don\'t really know what I\'m doing wrong. Hope someone can point out my mistakes (rookie here s

Answer 1

This might be what for looking for

//track mouse position on mousemove
var mousePosition;
//track state of mousedown and up
var isMouseDown;

//reference to the canvas element
var c = document.getElementById("myCanvas");
//reference to 2d context
var ctx = c.getContext("2d");

//add listeners
document.addEventListener('mousemove', move, false);
document.addEventListener('mousedown', setDraggable, false);
document.addEventListener('mouseup', setDraggable, false);

//make some circles
var c1 = new Circle(50, 50, 50, "red", "black");
var c2 = new Circle(200, 50, 50, "green", "black");
var c3 = new Circle(350, 50, 50, "blue", "black");
//make a collection of circles
var circles = [c1, c2, c3];

//main draw method
function draw() {
    //clear canvas
    ctx.clearRect(0, 0, c.width, c.height);
    drawCircles();
}

//draw circles
function drawCircles() {
    for (var i = circles.length - 1; i >= 0; i--) {
        circles[i].draw();
    }
}

//key track of circle focus and focused index
var focused = {
   key: 0,
   state: false
}

//circle Object
function Circle(x, y, r, fill, stroke) {
    this.startingAngle = 0;
    this.endAngle = 2 * Math.PI;
    this.x = x;
    this.y = y;
    this.r = r;

    this.fill = fill;
    this.stroke = stroke;

    this.draw = function () {
        ctx.beginPath();
        ctx.arc(this.x, this.y, this.r, this.startingAngle, this.endAngle);
        ctx.fillStyle = this.fill;
        ctx.lineWidth = 3;
        ctx.fill();
        ctx.strokeStyle = this.stroke;
        ctx.stroke();
    }
}

function move(e) {
    if (!isMouseDown) {
        return;
    }
    getMousePosition(e);
    //if any circle is focused
    if (focused.state) {
        circles[focused.key].x = mousePosition.x;
        circles[focused.key].y = mousePosition.y;
        draw();
        return;
    }
    //no circle currently focused check if circle is hovered
    for (var i = 0; i < circles.length; i++) {
        if (intersects(circles[i])) {
            circles.move(i, 0);
            focused.state = true;
            break;
        }
    }
    draw();
}

//set mousedown state
function setDraggable(e) {
    var t = e.type;
    if (t === "mousedown") {
        isMouseDown = true;
    } else if (t === "mouseup") {
        isMouseDown = false;
        releaseFocus();
    }
}

function releaseFocus() {
    focused.state = false;
}

function getMousePosition(e) {
    var rect = c.getBoundingClientRect();
    mousePosition = {
        x: Math.round(e.x - rect.left),
        y: Math.round(e.y - rect.top)
    }
}

//detects whether the mouse cursor is between x and y relative to the radius specified
function intersects(circle) {
    // subtract the x, y coordinates from the mouse position to get coordinates 
    // for the hotspot location and check against the area of the radius
    var areaX = mousePosition.x - circle.x;
    var areaY = mousePosition.y - circle.y;
    //return true if x^2 + y^2 <= radius squared.
    return areaX * areaX + areaY * areaY <= circle.r * circle.r;
}

Array.prototype.move = function (old_index, new_index) {
    if (new_index >= this.length) {
        var k = new_index - this.length;
        while ((k--) + 1) {
            this.push(undefined);
        }
    }
    this.splice(new_index, 0, this.splice(old_index, 1)[0]);
};
draw();

See this DEMO

Answer 2

There is a error here!

//no circle currently focused check if circle is hovered
for (var i = 0; i < circles.length; i++) {
    if (intersects(circles[i])) {
        circles.move(i, 0);
        focused.state = true;
        break;
    }
}
draw();

You need to use

cicles.move(i,i)