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JavaScript: Fun with Images

JavaScript: Fun with Images. Chapter 3 JavaScript for the WWW. Demos come mostly from text Website www.javascriptworld.com. Chapter 3 Demos in Text. Outline of Demos in C3. Rollovers (2 of 8 demo programs) Cycling Banners (0 of 4 demos) SlideShows (0 of 2 demos – use .ppt)

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JavaScript: Fun with Images

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  1. JavaScript: Fun with Images Chapter 3 JavaScript for the WWW

  2. Demos come mostly from text Website www.javascriptworld.com

  3. Chapter 3 Demos in Text

  4. Outline of Demos in C3 • Rollovers (2 of 8 demo programs) • Cycling Banners (0 of 4 demos) • SlideShows (0 of 2 demos – use .ppt) • Random Images (1 of 1 demo) • Rollover and Image Map (1 of 1 demo) • Auto change background colors (0 of 1 demo)

  5. <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML> <HEAD> <TITLE>A Simple Rollover</TITLE> </HEAD> <BODY BGCOLOR="WHITE"> <A HREF="next.html" onMouseover="document.arrow.src='redArrow.gif'" onMouseout="document.arrow.src='blueArrow.gif'"> <IMG SRC="blueArrow.gif" WIDTH="147" HEIGHT="82" BORDER="0" NAME="arrow" ALT="arrow"></A> </BODY> </HTML> RollOver.html

  6. Comments on this Simple RollOver • Note that the JS is invoked from attributes of HTML tags, not <SCRIPT> tags • It uses MouseOver event handlers in JS • This script does not download the images until they are needed. There might be a delay in the mouseover • In the floppy version, you can hear the browser getting the images from the diskette each time they are used. They are not cached in RAM. • It’s better to pre-fetch the images in the <HEAD>

  7. <HTML><HEAD> <TITLE>A Rollover with Pre-Fetching of Images</TITLE> <script> if (document.images) { img1 = new Image img2 = new Image img1.src = "blueArrow.gif" img2.src = "redArrow.gif" } else { img1.src = "" img2.src = "" document.arrow = "" } </script> </HEAD> <BODY BGCOLOR="WHITE"> <A HREF="next.html" onMouseover="document.arrow.src= img2.src" onMouseout="document.arrow.src=img1.src"><IMG SRC="blueArrow.gif" WIDTH="147" HEIGHT="82" BORDER="0" NAME="arrow" ALT="arrow"></A> </BODY> </HTML> RollOver2.html

  8. The next script puts a random image up on each visit • It uses an Array of 4 images # 0, 1, 2, 3. • Math.random() generates 0 < n < 1 • Then m=n*4 ranges from 0 to 3.999 • Math. floor(m) generates integer part of m, example floor(3.4) = 3 • This index picks one of the Array elements at random

  9. <HTML> <HEAD> <TITLE>Random Images</TITLE> <SCRIPT> myPix2 = new Array("images/callisto.jpg", "images/europa.jpg", "images/io.jpg", "images/ganymede.jpg") function choosePix() { if (document.images) { randomNum = Math.floor((Math.random() * myPix2.length)) document.myPicture2.src = myPix2[randomNum] }} </SCRIPT> </HEAD> <BODY BGCOLOR="WHITE" onLoad="choosePix()"> <IMG SRC="images/spacer.gif" WIDTH="262" HEIGHT="262" NAME="myPicture2" ALT="some image"> </BODY> </HTML> RandomImages1.html

  10. Image Maps in HTML • Use ISMAP to find coordinates of subparts of an image • Then put those coordinates into a shape • Demo is an American flag • After this demo, we will see how to combine image maps with rollovers in JS

  11. <html> <head> <title> Demo of Client Side Image Map </title> </head> <body> <h5> What do the symbols on the American flag mean? <br> (Click on the flag for answers) </h5> <!-- the ISMAP provides coordinates of the mouse location in the status bar <img src="USflag.gif" ISMAP> Then replace this tag with the one below. --> <img src="USflag.gif" USEMAP = "#flagmap"> <!-- now the image map--> <MAP NAME = "flagmap"> <AREA SHAPE = RECT COORDS ="0,0,81,60" HREF = stars.html> <AREA SHAPE = RECT COORDS ="81,0,192,112" HREF = bars.html> <AREA SHAPE = RECT COORDS ="0,60,81,112" HREF = bars.html> </MAP> </body> </html> A:/ImageMapDemo.html

  12. Combination of an Image Map with RollOvers • This can be used for an attractive navigation bar. • The hitch is creating nice graphics for each mouseover • The underlying links are not valid in the demo

  13. <HTML> <HEAD> <TITLE>Combining rollovers & image maps</TITLE> <SCRIPT > if (document.images) { img1 = new Image ; img2 = new Image; img3 = new Image imgRed = new Image img1.src = "images/testGreen1.gif“; img2.src = "images/testGreen2.gif" img3.src = "images/testGreen3.gif“; imgRed.src = "images/testRed.gif" } </SCRIPT> </HEAD> <BODY BGCOLOR="WHITE"> <MAP NAME="roll_map"> <AREA SHAPE="RECT" HREF="sec1.html" onMouseover="document.roll.src=img1.src" onMouseout="document.roll.src=imgRed.src" COORDS="0,0,120,60" ALT="Sample chapter"> <AREA SHAPE="RECT" HREF="sec2.html" onMouseover="document.roll.src=img2.src" onMouseout="document.roll.src=imgRed.src" COORDS="0,60,120,120" ALT="About the authors"> <AREA SHAPE="RECT" HREF="sec3.html" onMouseover="document.roll.src=img3.src" onMouseout="document.roll.src=imgRed.src" COORDS="0,120,120,180" ALT="Buy a copy"> </MAP> <A HREF="home.html" onMouseout="document.roll.src=imgRed.src"><IMG USEMAP="#roll_map" SRC="images/testRed.gif" WIDTH="120" HEIGHT="180" BORDER="0" NAME="roll" ALIGN="LEFT" HSPACE="20" ALT="Book info"></A> <H3>Thanks for visiting our site. Click on the box to the left.</H3> </BODY> </HTML> ImageMapRollOver.htm

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