Javascript draw dynamic line

Question

I'm looking for Javascript code for letting the user draw a line (on an image).

Just as the line tool in Photoshop (for example):

The user clicks on the image, drags the mouse (while the line between the start point and the mouse point is dynamically drawn on mouse drag).

I would also need a callable function to send the page the start and end coordinates.

I've found this very nice script for area selection: http://www.defusion.org.uk/code/javascript-image-cropper-ui-using-prototype-scriptaculous/

and I've found many script for drawing lines (and other shapes in JS), but could not find what I'm looking for.

Thanks

Answer 1

Since there is no standard method of drawing, if you want to support older browsers and IE, you will need to use a library. The library will handle the cross platform issues of drawing with SVG or Microsoft's VML

I recommend Raphael JS

Answer 2

raphael.js is a lightweight rendering tool for javascript (MIT licensed) which works in FF, Safari, Chrome and IE6+.

It uses SVG for the first 3 and VML for IE but the API is identical across browsers and very sweet.

http://raphaeljs.com/

e.g.

// Creates canvas 320 × 200 at 10, 50
var paper = Raphael(10, 50, 320, 200);

// Creates circle at x = 50, y = 40, with radius 10
var circle = paper.circle(50, 40, 10);
// Sets the fill attribute of the circle to red (#f00)
circle.attr("fill", "#f00");

// Sets the stroke attribute of the circle to white
circle.attr("stroke", "#fff"); 

I've used it to draw a line while dragging and can vouch for its ease of use

Answer 3

A cross-browser solution for drawing lines in javascript, without requiring any external libraries, can be found here: http://bytes.com/topic/javascript/answers/88771-drawing-vector-lines-javascript

This works in all browsers, including IE.

Answer 4

Consider using the canvas element to display the image. Then, drawing a line (or anything else) on it is trivial.

Answer 5

If your maths is good enough, it is possible (although mad) to do it without the canvas tag for most modern browsers using one of (as appropriate):

• -webkit-transform: rotate
• -moz-transform: rotate
• -o-transform-rotate
• The Trident Matrix Filter

By creating eg. a 1px high div, with eg. a border-top for your 'line', and using the mouse drag event to position and rotate it.

Madness lies this way but it would be a quite fun exercise. (You should use something like Raphael JS, which is cross browser and sane - see above)

Answer 6

i'm working on something similar. Drawing a line on a canvas is pretty simple. You can take from my code here.

http://p-func.com/html5_test/test2.html

Just follow the mousedown listener.

Although I have found, when wanting to load images, that the raphael library might be better to use. I saw this because Canvas seems to act like a flat image. So if I want to add an aimge to it, then allow the user to manipulate that image, it won't let me (unless there is something that i am missing).

Raphael allows you to draw and still use those drawings, and images, as objects.