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How to draw a line between two divs?

Posted by: admin November 30, 2017 Leave a comment

Questions:

I’m currently trying to draw a diagonal line between the bottom right corner of one div to the top right corner of another. If possible, I would like to do it without jQuery. Is this possible?

Answers:

http://jsfiddle.net/cnmsc1tm/

This won’t work with IE8 or below because of CSS limitations.

function getOffset( el ) {
    var rect = el.getBoundingClientRect();
    return {
        left: rect.left + window.pageXOffset,
        top: rect.top + window.pageYOffset,
        width: rect.width || el.offsetWidth,
        height: rect.height || el.offsetHeight
    };
}

function connect(div1, div2, color, thickness) { // draw a line connecting elements
    var off1 = getOffset(div1);
    var off2 = getOffset(div2);
    // bottom right
    var x1 = off1.left + off1.width;
    var y1 = off1.top + off1.height;
    // top right
    var x2 = off2.left + off2.width;
    var y2 = off2.top;
    // distance
    var length = Math.sqrt(((x2-x1) * (x2-x1)) + ((y2-y1) * (y2-y1)));
    // center
    var cx = ((x1 + x2) / 2) - (length / 2);
    var cy = ((y1 + y2) / 2) - (thickness / 2);
    // angle
    var angle = Math.atan2((y1-y2),(x1-x2))*(180/Math.PI);
    // make hr
    var htmlLine = "<div style='padding:0px; margin:0px; height:" + thickness + "px; background-color:" + color + "; line-height:1px; position:absolute; left:" + cx + "px; top:" + cy + "px; width:" + length + "px; -moz-transform:rotate(" + angle + "deg); -webkit-transform:rotate(" + angle + "deg); -o-transform:rotate(" + angle + "deg); -ms-transform:rotate(" + angle + "deg); transform:rotate(" + angle + "deg);' />";
    //
    // alert(htmlLine);
    document.body.innerHTML += htmlLine;
}
  • The Distance Formula
  • Finding the Center Of Two Points
  • Finding the Angle Between Two Points
  • CSS Transform:Rotate
  • HTML Element offset[Width|Height|Top|Left] properties

Edit (for others with the same problem):

If you need to, for example, create a line from two corners that are not the top right and bottom right divs, go to this section of the code:

// bottom right
var x1 = off1.left + off1.width;
var y1 = off1.top + off1.height;
// top right
var x2 = off2.left + off2.width;
var y2 = off2.top;

where you see + off1.width and + off1.height, that means that the code is calculating the position of the bottom or the right of the div. Remove the + off1.width or the + off1.height to get the left or the top of the div.

EDIT updated to a more standard getOffset function. If you want to get really anal you’d probably also have to add document.documentElement.client[Left/Top] and walk the offsetParent tree, but I think getBoundingClientRect() and window.page[X/Y]Offset are sufficient for an example like this.

Questions:
Answers:

There is a way to do it without jQ.

  1. Find the position of your divs using offset.
  2. Find the slope
  3. draw 1x1px points from start to end position using the slope in your loop.
Questions:
Answers:

Is using an image as the bottom border for that div class out of the question? If your diagonal line always has to be the same size/color, etc… that would be a non-jQuery option you could use.