ZeePedia buy college essays online


Introduction to Computing

<<< Previous IMAGES & ANIMATION Next >>>
 
img
Introduction to Computing ­ CS101
VU
LESSON 41
IMAGES & ANIMATION
(Web Development Lesson 14)
During the last Lesson we discussed String Manipulation
·
We became familiar with methods used for manipulating strings
·
We became able to solve simple problems involving strings
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
String Methods
FORMAT
string.methodName( )
EXAMPLE:
name = "Bhola" ;
document.write( name.toUpperCase( ) ) ;
BHOLABhola
document.write( name.bold( ) ) ;
Two Types of String Methods
1.HTML Shortcuts
bold( )
2.All Others
big( )
italics( )
String Methods: HTML Shortcuts
small( )
link( URL )
strike( )
fontsize( n )
sub( )
fixed( )
sup( )
fontcolor( color )
String Methods: All Others
charAt( n )
toLowerCase( )
substring( n, m )
toUpperCase( )
indexOf( substring, n )
lastIndexOf( substring, n )
split( delimiter )
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:
277
img
Introduction to Computing ­ CS101
VU
­
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
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
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
6.283185307179586
document.write( "2" * Math.PI ) ;
document.write( "Yes" ^ 43 ) ;
NaN
The `toString' Method
Explicit conversion to a string
EXAMPLE:
Convert 100.553478 into a currency format
a = 100.553478 ;
b = a.toString( ) ;
decimalPos = b.indexOf( ".", 0 ) ;
100.55
c = b.substring( 0, decimalPos + 3 ) ;
document.write( c ) ;
Conversion from Strings
parseInt( ) and parseFloat( ) methods
Today's Goal
(Images & Animation)
·
To become able to add and manipulate images and simple animations to a Web page
Images in HTML
·
It is quite straight forward to include gif and jpg images in an html Web page using the <IMG> tag
Format: <IMG src=URL, alt=text height=pixels width=pixels align="bottom|middle|top">
Plea: Don't use images just for the sake of it!
278
img
Introduction to Computing ­ CS101
VU
<HTML><HEAD>
<TITLE>Image Demo</TITLE>
</HEAD><BODY>
<H1>Image Demo</H1>
Here is an image <IMG src="die5.gif">
<IMG src="die5.gif" height="63"
width="126"> <P>
Here is another <IMG align="middle" src=
"http://www.vu.edu.pk/images/logo/logotop.jpg">
</BODY></HTML>
41.1 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.
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
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
Let us revisit an example that we first saw in Lesson 35
*
279
img
Introduction to Computing ­ CS101
VU
die3.gif
die2.gif
die1.gif
die6.gif
die5.gif
die4.gif
<HTML>
<HEAD>
<TITLE>Roll the Die</TITLE>
<SCRIPT>
JavaScript Code
</SCRIPT>
</HEAD>
<BODY >
HTML Code
</BODY>
</HTML>
<IMG name="die" src="die6.gif">
<FORM>
<INPUT type="button" value="Roll the Die"
onClick="rollDie( )">
</FORM>
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 ;
}
Another Example
·
Develop a Web page that displays six thumbnail images and a main image
280
img
Introduction to Computing ­ CS101
VU
·
The main image should change to a larger version of the thumbnail as soon as the mouse moves
over on a thumbnail image
<HTML>
<HEAD>
<TITLE>Image Selector</TITLE>
<SCRIPT>
JavaScript Code
</SCRIPT>
</HEAD>
<BODY >
HTML Code
</BODY>
</HTML>
dieImg = new Array( 7 ) ;
for( k = 1; k < 7; k = k + 1 ) { // Preload images
dieImg[ k ] = new Image( ) ;
dieImg[ k ].src = "die" + k + ".gif" ;
}
<IMG name="big" src="die6.gif" width="252" height="252"><P>
<IMG src="die1.gif" width="63" height="63"
onMouseOver=
"document.big.src=dieImg[ 1 ].src">
...
...
<IMG src="die6.gif" width="63" height="63"
onMouseOver=
"document.big.src=dieImg[ 6 ].src">
Where Else Can We Use This?
·
Automobile Web site
·
???
Animation Example 1
·
Take 16 images and cycle through them to create an animation effect
<HTML>
<HEAD>
<TITLE>Animation 1</TITLE>
<SCRIPT>
JavaScript Code
</SCRIPT>
</HEAD>
<BODY >
HTML Code
</BODY>
</HTML>
281
img
Introduction to Computing ­ CS101
VU
<CENTER>
<IMG name="circle" src="circle1.gif" onLoad="setTimeout( 'circulate( )', gap )">
</CENTER>
setTimeout( ) executes circulate( ) once after a delay of
gap = 100 ;
gap milliseconds
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" ;
2
4
1
3
6
5
7
8
10
12
9
11
16
14
13
15
function circulate( ) {
document.circle.src =
circImg[ imageN ].src ;
imageN = imageN + 1 ;
if( imageN > 16 )
imageN = 1 ;
}
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 <IMG> tag to display a moving image
·
However, JavaScript provides better control over the sequencing and the gap between the
individual images
282
img
Introduction to Computing ­ CS101
VU
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
<HTML>
<HEAD>
<TITLE>Animation 2</TITLE>
<SCRIPT>
JavaScript Code
</SCRIPT>
</HEAD>
<BODY >
HTML Code
</BODY>
</HTML>
<CENTER>
<IMG name="circle" src="circle1.gif" onLoad="setTimeout( 'circulate( )',
gap )">
</CENTER>
<FORM>
<INPUT type="button" value="Slow Down"
onClick="slowDown( )">
<INPUT type="button" value="Speed Up"
onClick="speedUp( )">
</FORM>
gap = 100 ;
imageN = 1 ;
circImg = new Array( 17 ) ;
No change
for( k = 1; k < 17; k = k + 1 ) { // Preload images
circImg[ k ] = new Image( ) ;
circImg[ k ].src = "circle" + k + ".gif" ;
}
function circulate( ) {
document.circle.src =
circImg[ imageN ].src ;
No change
imageN = imageN + 1 ;
if( imageN > 16 )
imageN = 1 ;
}
Two new
function slowDown( ) {
functions
gap = gap + 20 ;
if( gap > 4000 )
gap = 4000 ;
}
function speedUp( ) {
gap = gap - 20 ;
if( gap < 0 )
gap = 0 ;
}
283
img
Introduction to Computing ­ CS101
VU
41.2 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
Structured Vector Graphics
·
New format; may become more popular than Flash
·
Plug-in required
·
Text-file storage; search engine friendly
During Today's Lesson ...
·
We became able to add and manipulate images and simple animations to a Web page
Our 15th & 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
284
Table of Contents:
  1. INTRODUCTION
  2. EVOLUTION OF COMPUTING
  3. World Wide Web, Web’s structure, genesis, its evolution
  4. Types of Computers, Components, Parts of Computers
  5. List of Parts of Computers
  6. Develop your Personal Web Page: HTML
  7. Microprocessor, Bus interface unit, Data & instruction cache memory, ALU
  8. Number systems, binary numbers, NOT, AND, OR and XOR logic operations
  9. structure of HTML tags, types of lists in web development
  10. COMPUTER SOFTWARE: Operating Systems, Device Drivers, Trialware
  11. Operating System: functions, components, types of operating systems
  12. Forms on Web pages, Components of Forms, building interactive Forms
  13. APPLICATION SOFTWARE: Scientific, engineering, graphics, Business, Productivity, Entertainment, Educational Software
  14. WORD PROCESSING: Common functions of word processors, desktop publishing
  15. Interactivity to Forms, JavaScript, server-side scripts
  16. ALGORITHMS
  17. ALGORITHMS: Pseudo code, Flowcharts
  18. JavaScript and client-side scripting, objects in JavaScript
  19. Low, High-Level, interpreted, compiled, structured & object-oriented programming languages
  20. Software Design and Development Methodologies
  21. DATA TYPES & OPERATORS
  22. SPREADSHEETS
  23. FLOW CONTROL & LOOPS
  24. DESIGN HEURISTICS. Rule of thumb learned through trial & error
  25. WEB DESIGN FOR USABILITY
  26. ARRAYS
  27. COMPUTER NETWORKS: types of networks, networking topologies and protocols
  28. THE INTERNET
  29. Variables: Local and Global Variables
  30. Internet Services: FTP, Telnet, Web, eMail, Instant messaging, VoIP
  31. DEVELOPING PRESENTATIONS: Effective Multimedia Presentations
  32. Event Handlers
  33. GRAPHICS & ANIMATION
  34. INTELLIGENT SYSTEMS: techniques for designing Artificial Intelligent Systems
  35. Mathematical Functions in JavaScript
  36. DATA MANAGEMENT
  37. DATABASE SOFTWARE: Data Security, Data Integrity, Integrity, Accessibility, DBMS
  38. String Manipulations:
  39. CYBER CRIME
  40. Social Implications of Computing
  41. IMAGES & ANIMATION
  42. THE COMPUTING PROFESSION
  43. THE FUTURE OF COMPUTING
  44. PROGRAMMING METHODOLOGY
  45. REVIEW & WRAP-UP of Introduction to Computing