CSS Vertical Text Typography | CSS Writing-mode & Text-orientation Property

CSS Vertical Text Typography | CSS Writing-mode & Text-orientation Property

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Navigating Between DOM Nodes in JavaScript

In the previous chapters you've learnt how to select individual elements on a web page. But there are many occasions where you need to access a child, parent or ancestor element. See the JavaScript DOM nodes chapter to understand the logical relationships between the nodes in a DOM tree.

DOM node provides several properties and methods that allow you to navigate or traverse through the tree structure of the DOM and make changes very easily. In the following section we will learn how to navigate up, down, and sideways in the DOM tree using JavaScript.

Accessing the Child Nodes

You can use the firstChild and lastChild properties of the DOM node to access the first and last direct child node of a node, respectively. If the node doesn't have any child element, it returns null.

Example

<div id="main">
    <h1 id="title">My Heading</h1>
    <p id="hint"><span>This is some text.</span></p>
</div>

<script>
var main = document.getElementById("main");
console.log(main.firstChild.nodeName); // Prints: #text

var hint = document.getElementById("hint");
console.log(hint.firstChild.nodeName); // Prints: SPAN
</script>

Note: The nodeName is a read-only property that returns the name of the current node as a string. For example, it returns the tag name for element node, #text for text node, #comment for comment node, #document for document node, and so on.

If you notice the above example, the nodeName of the first-child node of the main DIV element returns #text instead of H1. Because, whitespace such as spaces, tabs, newlines, etc. are valid characters and they form #text nodes and become a part of the DOM tree. Therefore, since the <div> tag contains a newline before the <h1> tag, so it will create a #text node.

To avoid the issue with firstChild and lastChild returning #text or #comment nodes, you could alternatively use the firstElementChild and lastElementChild properties to return only the first and last element node, respectively. But, it will not work in IE 9 and earlier.

Example

<div id="main">
    <h1 id="title">My Heading</h1>
    <p id="hint"><span>This is some text.</span></p>
</div>

<script>
var main = document.getElementById("main");
alert(main.firstElementChild.nodeName); // Outputs: H1
main.firstElementChild.style.color = "red";

var hint = document.getElementById("hint");
alert(hint.firstElementChild.nodeName); // Outputs: SPAN
hint.firstElementChild.style.color = "blue";
</script>

Similarly, you can use the childNodes property to access all child nodes of a given element, where the first child node is assigned index 0. Here's an example:

Example

<div id="main">
    <h1 id="title">My Heading</h1>
    <p id="hint"><span>This is some text.</span></p>
</div>

<script>
var main = document.getElementById("main");

// First check that the element has child nodes 
if(main.hasChildNodes()) {
    var nodes = main.childNodes;
    
    // Loop through node list and display node name
    for(var i = 0; i < nodes.length; i++) {
        alert(nodes[i].nodeName);
    }
}
</script>

The childNodes returns all child nodes, including non-element nodes like text and comment nodes. To get a collection of only elements, use children property instead.

Example

<div id="main">
    <h1 id="title">My Heading</h1>
    <p id="hint"><span>This is some text.</span></p>
</div>

<script>
var main = document.getElementById("main");

// First check that the element has child nodes 
if(main.hasChildNodes()) {
    var nodes = main.children;
    
    // Loop through node list and display node name
    for(var i = 0; i < nodes.length; i++) {
        alert(nodes[i].nodeName);
    }
}
</script>

#javascript 

CSS Vertical Text Typography | CSS Writing-mode & Text-orientation Property

CSS Vertical Text Typography | CSS Writing-mode & Text-orientation Property

#css #programming #web-development

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Position Layout property in CSS

Hello, World! In this article, we will try to grasp the concepts of one of the trickiest and crucial topics in CSS.

Position layout property in CSS is solely used to place and position elements respectively in an HTML document. They assign respective positions to HTML elements so that the overall design of our page is maintained and managed well.

The widely used positions property in CSS are as follows:

1. Static position:

When an HTML element gets assigned with

staticposition, the various position properties likeleft,right,topandbottomdoesn’t work. Elements in an HTML document carry static position by default.

Let’s copy and paste the code below in an IDE to view what’s happening.

<!DOCTYPE html>
<html lang="en">
  <head>
    <style>
      #Section {
        height: 200vh;
        width: 800px;
        border: 5px solid blue;
        background-color: cyan;
        font-family: monospace;
        font-size: 2rem;
        text-align: center; 
      }

      #Div1, #Div2, #Div3 {
        border: 4px solid red;
        font-size: 1.5rem;
        width: 200px;
        height: 100px;
        text-align: center;
        display: inline-block;
      }

      #Div2 {
        position: static;
        left: 20px;
        top: 50px;
      }
    </style>
  </head>
  <body>
    <section id="Section">
      <p>This is Section</p>
      <div id="Div1">
        <p>This is Div 1</p>
      </div>
      <div id="Div2">
        <p>This is Div 2</p>
      </div>
      <div id="Div3">
        <p>This is Div 3</p>
      </div>
    <section>
  </body>
</html>

Upon adding position property

staticto the selector idDiv2, we saw that the position ofDiv2box didn’t change. Hence, we can conclude that elements with positionstaticdoesn’t get affected byleft, right,toporbottomproperties.

2. Relative position:

When an element gets assigned with position

relative, the position properties likeleft,right,top andbottomaffects the element’s position in the page relative to its normal position asstatic.

Let’s copy and paste the code below to

Div2selector to replace the previous position property.

#Div2 {
        position: relative;
        left: 20px;
        top: 50px;
      }

We can see that the

Div2box changed its position relative to its normal orstaticposition, i.e.20pxfrom theleftand50pxfrom thetop. Upon applyingrelativeposition property to an element, other contents in the same box won’t get affected and change positions

3. Fixed position:

This position property is used to freeze an element in a particular location of the page so that scrolling doesn’t affect the visibility or location of the element. When we apply

fixedvalue to a selector, it gets removed from the flow of the HTML document, i.e. the selector element gets uprooted from its actual position, becomes relative to the entire viewport, and doesn’t get scrolled.

Let’s copy and paste the code below to know the difference.

<!DOCTYPE html>
<html lang="en">
  <head>
    <style>
      #Section {
        height: 400vh;
        width: 800px;
        border: 5px solid blue;
        background-color: cyan;
        font-family: monospace;
        font-size: 2rem;
        text-align: center; 
      }
      #Div1, #Div2, #Div3 {
        border: 4px solid red;
        font-size: 1.5rem;
        width: 200px;
        height: 100px;
        text-align: center;
        display: inline-block;
      }
      #Div2 {
        position: fixed;
        left: 0;
        top: 0;
      }
    </style>
  </head>
  <body>
    <section id="Section">
      <p>This is Section</p>
      <div id="Div1">
        <p>This is Div 1</p>
      </div>
      <div id="Div2">
        <p>This is Div 2</p>
      </div>
      <div id="Div3">
        <p>This is Div 3</p>
      </div>
    <section>
  </body>
</html>

After scrolling, we can see that the id

Div2gets fixed in the topmost corner of the document.

4. Absolute position:

Just like

fixedposition, theabsoluteposition property removes selectors from the flow. As the element gets removed from its normal position, the parent element doesn’t regard it as its child anymore. The element becomes relative to the document.

#css #css3 #css-position-property #tutorials #learning-css #html-css

OpenCV putText() - Writing Text on Images

Hello fellow learner! In this tutorial, we will learn how to write string text on Images in Python using the OpenCV putText() method. So let’s get started.

Table of Contents

What is the OpenCV putText() method?

OpenCV Python is a library of programming functions mainly aimed at real-time computer vision and image processing problems.

OpenCV contains putText() method which is used to put text on any image. The method uses following parameters.

• img: The Image on which you want to write the text.
• text: The text you want to write on the image.
• org: It is the coordinates of the Bottom-Left corner of your text. It is represented as a tuple of 2 values (X, Y). X represents the distance from the left edge and Y represents the distance from the top edge of the image.
• fontFace: It denotes the type of font you want to use. OpenCV supports only a subset of Hershey Fonts.
• FONT_HERSHEY_SIMPLEX
• FONT_HERSHEY_PLAIN
• FONT_HERSHEY_DUPLEX
• FONT_HERSHEY_COMPLEX
• FONT_HERSHEY_TRIPLEX
• FONT_HERSHEY_COMPLEX_SMALL
• FONT_HERSHEY_SCRIPT_SIMPLEX
• FONT_HERSHEY_SCRIPT_COMPLEX
• FONT_ITALIC
• fontScale: It is used to increase/decrease the size of your text. The font scale factor is multiplied by the font-specific base size.
• color: It represents the color of the text that you want to give. It takes the value in BGR format, i.e., first blue color value, then green color value, and the red color value all in range 0 to 255.
• thickness (Optional): It represents the thickness of the lines used to draw a text. The default value is 1.
• lineType (Optional): It denotes the type of line you want to use. 4 LineTypes available are
• FILLED
• LINE_4
• LINE_8 (Default)
• LINE_AA
• bottomLeftOrigin (Optional): When true, the image data origin is at the bottom-left corner. Otherwise, it is at the top-left corner. The default value is False.

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