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1 CS101 Introduction to Computing Lecture 41 Images & Animation (Web Development Lecture 14)

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Presentation on theme: "1 CS101 Introduction to Computing Lecture 41 Images & Animation (Web Development Lecture 14)"— Presentation transcript:

1 1 CS101 Introduction to Computing Lecture 41 Images & Animation (Web Development Lecture 14)

2 2 During the last lecture we discussed String Manipulation We became familiar with methods used for manipulating strings We became able to solve simple problems involving strings

3 3 String Manipulation in JavaScript In addition to the concatenation operator (+) JavaScript supports several advanced string operations as well Notationaly, these functions are accessed by referring to various methods of the String object Moreover, this object also contains the ‘length’ property

4 4 String Methods FORMAT string.methodName( ) EXAMPLE: name = “Bhola” ; document.write( name.toUpperCase( ) ) ; document.write( name.bold( ) ) ; BHOLABhola

5 5 Two Types of String Methods 1.HTML Shortcuts 2.All Others

6 6 String Methods: HTML Shortcuts bold( ) italics( ) strike( ) sub( ) sup( ) big( ) small( ) fontsize( n ) fixed( ) fontcolor( color ) link( URL )

7 7 String Methods: All Others split( delimiter ) toLowerCase( ) toUpperCase( ) charAt( n ) substring( n, m ) indexOf( substring, n ) lastIndexOf( substring, n )

8 8 Automatic Conversion to Strings Whenever a non-string is used where JavaScript is expecting a string, it converts that non-string into a string Example: –The document.write( ) method expects a string (or several strings, separated by commas) as its argument –When a number or a Boolean is passed as an argument to this method, JavaScript automatically converts it into a string before writing it onto the document

9 9 The ‘+’ Operator When ‘+’ is used with numeric operands, it adds them When it is used with string operands, it concatenates them When one operand is a string, and the other is not, the non-string will first be converted to a string and then the two strings will be concatenated

10 10 Strings In Mathematical Expressions When a string is used in a mathematical context, if appropriate, JavaScript first converts it into a number. Otherwise, a “NaN” is the result document.write( "2" * Math.PI ) ; document.write( "Yes" ^ 43 ) ; NaN

11 11 The ‘toString’ Method Explicit conversion to a string EXAMPLE: Convert into a currency format a = ; b = a.toString( ) ; decimalPos = b.indexOf( ".", 0 ) ; c = b.substring( 0, decimalPos + 3 ) ; document.write( c ) ;

12 12 Conversion from Strings parseInt( ) and parseFloat( ) methods

13 13 Today’s Goal (Images & Animation) To become able to add and manipulate images and simple animations to a Web page

14 14 Images in HTML It is quite straight forward to include gif and jpg images in an html Web page using the tag Format: text Plea: Don’t use images just for the sake of it!

15 15

16 16 Image Demo Image Demo Here is an image Here is another

17 17 Images in JavaScript Images in JavaScript can be manipulated in many ways using the built-in object Image Properties: name, border, complete, height, width, hspace, vspace, lowsrc, src Methods: None Event handlers: onAbort, onError, onLoad, etc.

18 18 Image Preloading The primary use for an Image object is to download an image into the cache before it is actually needed for display This technique can be used to create smooth animations or to display one of several images based on the requirement

19 19 The Image Pre-Loading Process 1.An instance of the Image object is created using the new keyword 2.The src property of this instance is set equal to the filename of the image to be pre-loaded 3.That step starts the down-loading of the image into the cache without actually displaying it 4.When a pre-loaded image is required to be displayed, the src property of the displayed image is set to the src property of the pre- fetched image

20 20 Let us revisit an example that we first saw in lecture 35

21 21 * *

22 22

23 23 die1.gifdie2.gifdie3.gif die4.gifdie5.gifdie6.gif

24 24 Roll the Die JavaScript Code HTML Code

25 25

26 26 dieImg = new Array( 7 ) ; for( k = 1; k < 7; k = k + 1 ) { //Preload images dieImg[ k ] = new Image( ) ; dieImg[ k ].src = "die" + k + ".gif" ; } function rollDie( ) { dieN = Math.ceil( 6 * Math.random( ) ) ; document.die.src = dieImg[ dieN ].src ; }

27 27 Another Example Develop a Web page that displays six thumbnail images and a main image The main image should change to a larger version of the thumbnail as soon as the mouse moves over on a thumbnail image

28 28

29 29 Image Selector JavaScript Code HTML Code

30 30 dieImg = new Array( 7 ) ; for( k = 1; k < 7; k = k + 1 ) { // Preload images dieImg[ k ] = new Image( ) ; dieImg[ k ].src = "die" + k + ".gif" ; }

31 31

32 32 Where Else Can We Use This? Automobile Web site ???

33 33 Animation Example 1 Take 16 images and cycle through them to create an animation effect

34

35 35

36 36 Animation 1 JavaScript Code HTML Code

37 37 setTimeout( ) executes circulate( ) once after a delay of gap milliseconds

38 38 gap = 100 ; imageN = 1 ; circImg = new Array( 17 ) ; for( k = 1; k < 17; k = k + 1 ) { // Preload images circImg[ k ] = new Image( ) ; circImg[ k ].src = "circle" + k + ".gif" ; }

39 39 function circulate( ) { document.circle.src = circImg[ imageN ].src ; imageN = imageN + 1 ; if( imageN > 16 ) imageN = 1 ; }

40 40

41 41 Animated Gifs We could have saved the 16 gif images of the previous example in a single file in the form of an animated gif, and then used it in a regular tag to display a moving image However, JavaScript provides better control over the sequencing and the gap between the individual images

42 42 Animation Example 2 Take 16 images and cycle through them to create an animation effect Provide buttons to slow down or speed up the animation

43 43

44 44 Animation 2 JavaScript Code HTML Code

45 45

46 46 gap = 100 ; imageN = 1 ; circImg = new Array( 17 ) ; for( k = 1; k < 17; k = k + 1 ) { // Preload images circImg[ k ] = new Image( ) ; circImg[ k ].src = "circle" + k + ".gif" ; } No change

47 47 function circulate( ) { document.circle.src = circImg[ imageN ].src ; imageN = imageN + 1 ; if( imageN > 16 ) imageN = 1 ; } No change

48 48 function slowDown( ) { gap = gap + 20 ; if( gap > 4000 ) gap = 4000 ; } function speedUp( ) { gap = gap - 20 ; if( gap < 0 ) gap = 0 ; } Two new functions

49 49

50 50 Flash Animation Designed for 2-D animations, but can be used for storing static vector-images as well A special program (called a plug-in) is required to view Flash files in a Web browser Can be used to design complete, animated Web sites with hardly any HTML in it Binary-file storage

51 51 Structured Vector Graphics New format; may become more popular than Flash Plug-in required Text-file storage; search engine friendly

52 52 During Today’s Lecture … We became able to add and manipulate images and simple animations to a Web page

53 53 Our 15 th & Final Web Dev Lecture: ( Programming Methodology) To understand effective programming practices that result in the development of correct programs with minimum effort To become familiar with simple debugging techniques


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