CSS Visual Formatting Model

CSSWeb DevelopmentFront End Technology

The CSS Visual Formatting is a model corresponding to an algorithm which processes and transforms each element of the document to generate one or more boxes that conform to CSS Box Model.

The layout of generated boxes depends on several properties such as −

  • Dimensions
  • Type − atomic inline-level, block, inline, or inline-block
  • Positioning − absolute, float, or normal
  • Relation with child and neighbor elements of document
  • External Information − viewport’s and image’s width - height, etc.

CSS Box Generation of processed elements −

  • Block level
    • These elements force line break above and below themselves and take up the available whole width even though their content doesn’t require it.
    • For example: Divisions (<div>), Heading (<h1> to <h6>), etc.
  • Inline level
    • These elements do not force line break above and below themselves and take up only the required width for the content.
    • For example: Spans (<span>), Strong element (<strong>)

Example

Let’s see an example of block level box generation −

 Live Demo

<!DOCTYPE html>
<html>
<head>
<title>HTML Heading</title>
<style>
form {
   width:70%;
   margin: 0 auto;
   text-align: center;
}
* {
   padding: 2px;
   margin:5px;
}
input[type="button"] {
   border-radius: 10px;
}
#headingPreview h2{
   background-color: #DC3545;
}
</style>
</head>
<body>
<form>
<fieldset>
<legend>HTML Heading</legend>
<input type="text" id="textSelect" placeholder="Type Heading Here...">
<div id="radioBut">
<label>H1</label><input class="radio" type="radio" name="heading" value="h1" checked >
<label>H2</label><input class="radio" type="radio" name="heading" value="h2">
<label>H3</label><input class="radio" type="radio" name="heading" value="h3">
<label>H4</label><input class="radio" type="radio" name="heading" value="h4">
<label>H5</label><input class="radio" type="radio" name="heading" value="h5">
<label>H6</label><input class="radio" type="radio" name="heading" value="h6">
</div>
<div>Heading Preview: <span id="headingPreview">Output will show up here</span></div>
<input type="button" onclick="changeHeading()" value="Preview">
</fieldset></form>
<script>
var textSelect = document.getElementById("textSelect");
var headingPreview = document.getElementById("headingPreview");
function changeHeading() {
   if(textSelect.value === '')
      headingPreview.innerHTML = 'Write a Heading';
   else{
      for(var i=0; i<6; i++){
         var radInp = document.getElementsByClassName('radio')[i];
         if(radInp.checked === true && textSelect.value !== ''){
            headingPreview.innerHTML = '<'+radInp.value+'>'+textSelect.value+'</'+radInp.value+'>';
            headingPreview.innerHTML += '<'+radInp.value+'>'+textSelect.value+'</'+radInp.value+'>';
         }
      }
   }
}
</script></body></html>

Output

This will produce the following output −

After clicking ‘Preview’ button with text field empty −

After clicking ‘Preview’ button with text field not empty and ‘h2’ radio button checked −

Example

Let’s see an example for inline level box generation −

 Live Demo

<!DOCTYPE html>
<html>
<head>
<title>em element</title>
<style>
form {
   width:70%;
   margin: 0 auto;
   text-align: center;
}
* {
   padding: 2px;
   margin:5px;
}
input[type="button"] {
   border-radius: 10px;
}
em{
   background-color: #FF8A00;
}
</style>
</head>
<body>
<form>
<fieldset>
<legend>em-element</legend>
<label for="textSelect">Formatter: </label>
<input id="textSelect" type="text" placeholder="John Doe">
<input type="button" onclick="convertItalic()" value="Check">
<div id="divDisplay"></div>
</fieldset>
</form>
<script>
var divDisplay = document.getElementById("divDisplay");
var textSelect = document.getElementById("textSelect");
function convertItalic() {
   for(i=0; i<2; i++){
      var italicObject = document.createElement("EM");
      var italicText = document.createTextNode(textSelect.value);
      italicObject.appendChild(italicText);
      divDisplay.appendChild(italicObject);
   }
}
</script>
</body>
</html>

Output

This will produce the following output −

Before clicking ‘Check’ button −

After clicking ‘Check’ button −

raja
Published on 07-Jan-2020 11:09:41
Advertisements