#A sketch like ruler in javascript 中文介绍

###Introduction

Ruler.js is a jQuery plugin based on HTML5 (canvas) which provide you two sketch like rulers (vertical and horizontal) at the left and top of a divor other block-level HTML Element.

Sometimes, a div contains so many elements in it that you have to add a scroll bar. In this scene, you might want to know the exact position of the elements in your eyes when scrolling is carried out.

####Ruler.js will help you like that: Use Case . Any issue will be appreciated.

###Usage

1. Include jquery and ruler.js in your HTML document

2. set the container element's style

    #demo{
    	position:absolute;
    	/* fixed and relative is alse supposed */
    	width: 200px; 
    	height: 200px;
    	/* width and height as you need */
    }

3. use ruler.js to add rulers on div#demo like this

    var ruler = $('#demo').getRuler()
   	

   or configure parameters according to need

    var ruler = $('#demo').getRuler({
      startX: -240,  // the start peg of the horizontal ruler
      startY: -100,  // the start peg of the vertical ruler
      thick: 30,  // the width of both ruler
      fgColor: '#F5F5F5', // the foreground color of ruler
      bgColor: '#999',	// the background color of ruler
      shadowColor: '#CCC', // the shadow's color when you call the method 'setSelect()'
      font: '15px -apple-system, '.SFNSText'Regular', "SF'UI Text", "Helvetica Neue", Arial, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "WenQuanYi Zen Hei", sans-serif',
      // * Be careful! the font's size is expected to be the size of the n multiple (n equils to the parameter 'ratio')
      fontColor: '#000', // the value tag's color on ruler
      ratio: 2, // canvas PixelRatio, 1 on ordinary display, 2 on retina
      perWidth: 10 // width between two pegs
    });

4. update ruler when the container scroll

    $('#demo').css({
      overflow: 'scroll'  //assign 'scroll' to the 'overflow' attribute 
    }).on('scroll', function(event) {
      event.preventDefault();
      ruler.update();
    });

5. you can alse draw a shadow on the ruler by the method setSelect(x, y, width, height), in this example, you can click the colorful div like That

6. By the way, the ruler is clickable to draw align line on it, the align line can be deleted when hover on it.Both will trigger a jQuery event, you can listene the event setAlignLine like this

    $(document.body).on('setAlignLine', function(event, position) {
    	event.preventDefault();
        console.log('Horizontal', position.horValue)
        console.log('Vertical', position.verValue)
    });

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