Tự học HTML và CSS trong 1 giờ - part 28 pot

ptg A circular region A polygonal region A rectangular region The Mapedit program for Windows, Linux, and the Mac OS can help you create client- side imagemaps. You can find it online at http://www.boutell.com/mapedit/. In addition, many of the latest WYSIWYG editors for HTML pages and Web graphics enable you to generate imagemaps. There’s a Web-based editor for imagemaps that you can try out at http://www.image-maps.com/; it creates both imagemaps and the CSS equivalents. If you must create your imagemaps by hand, here’s how. First, make a sketch of the regions that will be active on your image. Figure 9.25 shows the three types of shapes that you can specify in an imagemap: circles, rectangles, and polygons. 246 LESSON 9: Adding Images, Color, and Backgrounds FIGURE 9.25 Three types of shapes are avail- able for creating imagemaps. You next need to determine the coordinates for the endpoints of those regions. Most image-editing programs have an option that displays the coordinates of the current mouse position. Use this feature to note the appropriate coordinates. (All the mapping programs mentioned previously will create the <map> tag for you, but for now, following the steps manually will help you better understand the processes involved.) Defining a Polygon Figure 9.26 shows the x,y coordinates of a polygon region. These values are based on their positions from the upper-left corner of the image, which is coordinate 0,0. The first number in the coordinate pair indicates the x value and defines the number of pixels from the extreme left of the image. The second number in the pair indicates the y mea- surement and defines the number of pixels from the top of the image. Download from www.wowebook.com ptg (0,0) (229,66) (333,94) (332,19) (276,19) (263,94) Defining a Circle Figure 9.27 shows how to get the coordinates for circles. Here you note the coordinates for the center point of the circle and the radius, in pixels. The center point of the circle is defined as the x,y coordinate from the upper-left corner of the image. What Is an Imagemap? 247 9 The 0,0 origin is in the upper-left corner of the image, and positive y is down. NOTE FIGURE 9.26 Getting the coordinates for a polygon. (0,0) Center (121,79) Radius of circle=66 pixels FIGURE 9.27 Getting the coordi- nates for a circle. Download from www.wowebook.com ptg Defining a Rectangle Figure 9.28 shows how to obtain coordinates for rectangle regions. Note the x,y coordi- nates for the upper-left and lower-right corners of the rectangle. 248 LESSON 9: Adding Images, Color, and Backgrounds FIGURE 9.28 Getting the coordinates for a rectangle. (0,0) Top Left (342,19) Bottom right (440,318) The <map> and <area> Tags If you’re creating your imagemap manually and you’ve written down all the coordinates for your regions and the URLs they’ll point to, you can include this information in the client-side imagemap tags on a web page. To include a client-side imagemap inside an HTML document, use the <map> tag, which looks like the following: <map name=“mapname”> coordinates and links </map> The value assigned to the name attribute is the name of this map definition. This is the name that will be used later to associate the clickable image with its corresponding coor- dinates and hyperlink references. So, if you have multiple imagemaps on the same page, you can have multiple <map> tags with different names. Between the <map> and the </map> tags, enter the coordinates for each area in the imagemap and the destinations of those regions. The coordinates are defined inside yet another new tag: the <area> tag. To define a rectangle, for example, you would write the following: <area shape=“rect” coords=“41,16,101,32” href=“test.html”> The type of shape to be used for the region is declared by the shape attribute, which can have the values rect, poly, circle, and default. The coordinates for each shape are Download from www.wowebook.com ptg noted using the coords attribute. For example, the coords attribute for a poly shape appears as follows: <area shape=“poly” coords=“x1,y1,x2,y2,x3,y3, ,xN,yN” href=“URL”> Each x,y combination represents a point on the polygon. For rect shapes, x1,y1 is the upper-left corner of the rectangle, and x2,y2 is the lower-right corner: <area shape=“rect” coords=“x1,y1,x2,y2” href=“URL”> For circle shapes, x,y represents the center of a circular region of size radius: <area shape=“circle” coords=“x,y,radius” href=“URL”> The default shape is different from the others—it doesn’t require any coordinates to be specified. Instead, the link associated with the default shape is followed if the user clicks anywhere on the image that doesn’t fall within another defined region. Another attribute you need to define for each <area> tag is the href attribute. You can assign href any URL you usually would associate with an <a> link, including relative pathnames. In addition, you can assign href a value of “nohref” to define regions of the image that don’t contain links to a new page. What Is an Imagemap? 249 9 If you’re using client-side imagemaps with frames, you can include the target attribute inside an <area> tag to open a new page in a specific window, as in this example: <area shape=“rect” coords=“x1,y1,x2,y2” href=“URL” target= “window_name”> You need to include one more attribute in HTML5. Earlier in this lesson, you learned how to specify alternate text for images. In HTML5, the alt attribute is an additional requirement for the <area> tag that displays a short description of a clickable area on a client-side imagemap when you pass your cursor over it. Using the <area> example that I cited, the alt attribute appears as shown in the following example: <area shape=“rect” coords=“41,16,101,32” href=“test.html” alt=“test link”> The usemap Attribute After you’ve created your <map> tag and defined the regions of your image using <area> tags, the next step is to associate the map with the image. To do so, the usemap attribute of the <img> tag is used. The map name that you specified using the name attribute of the <map> tag, preceded by a #, should be used as the value of the usemap attribute, as shown in this example: <img src=“image.gif” usemap=“#mapname”> NOTE Download from www.wowebook.com ptg ▼ 250 LESSON 9: Adding Images, Color, and Backgrounds The value assigned to usemap is a standard URL. This is why map- name has a pound symbol (#) in front of it. As with links to anchors inside a web page, the pound symbol tells the browser to look for mapname in the current web page. If you have a complex imagemap, however, you can store it in a separate HTML file and reference it using a standard URL. Task: Exercise 9.3: A Clickable Jukebox Let’s take a look at how to create a client-side imagemap for a real image. In this exam- ple, you define clickable regions on an image of a jukebox. The image you use appears in Figure 9.29. NOTE FIGURE 9.29 The jukebox image. First, define the regions that will be clickable on this image. There are six rectangular buttons with musical categories on them, a center area that looks like a house, and a circle with a question mark inside it. Figure 9.30 shows regions on the image. FIGURE 9.30 The jukebox with areas defined. Polygon Circle Rectangle Rectangle , Download from www.wowebook.com ptg Now that you know where the various regions are, you need to find the exact coordinates of the areas as they appear in your image. You can use a mapping program like Mapedit, or you can do it manually. If you try it manually, it’s helpful to keep in mind that most image-editing programs display the x and y coordinate of the image when you move the mouse over it. What Is an Imagemap? 251 9 , Getting Image Coordinates from the Browser You don’t have an image-editing program? If you use Firefox as your browser, here’s a trick: Create an HTML file with the image inside a link pointing to a fake file, and include the ismap attribute inside the <img> tag. You don’t need a real link; anything will do. The HTML code might look something like the following: <a href=“nothing”><img src=“myimage.gif” ismap></a> When you load this into your browser, the image displays as if it were an imagemap. When you move your mouse over it, the x and y coordinates appear in the status line of the browser. Using this trick, you can find the coordinates for the map file of any point on that image. With regions and a list of coordinates, all you need are the web pages to jump to when the appropriate area is selected. These can be documents, scripts, or anything else you can call from a browser as a jump destination. For this example, I’ve created several doc- uments and stored them inside the music directory on my Web server. These are the pages you’ll define as the end points when the clickable images are selected. Figure 9.31 identifies each of the eight clickable areas in the imagemap. Table 9.1 shows the coordi- nates of each and the URL that’s called up when it’s clicked. TABLE 9.1 Clickable Areas in the Jukebox Image Number Type URL Coordinates 1 rect music/classics.html 101,113,165,134 2 rect music/country.html 101,139,165,159 3 rect music/rockpop.html 101,163,165,183 4 poly music/home.html 175,152,203,118 220,118,247,152 237,153,237,181 186,181,186,153 , Download from www.wowebook.com ptg TABLE 9.1 Continued Number Type URL Coordinates 5 rect music/swing.html 259,113,323,134 6 rect music/jazz.html 259,139,323,159 7 rect music/gospel.html 259,163,323,183 8 circle music/help.html 379,152,21 252 LESSON 9: Adding Images, Color, and Backgrounds 5 1 8 2 3 4 7 6 FIGURE 9.31 Eight hot spots, numbered as iden- tified in Table 9.1. For the jukebox image, the <map> tag and its associated <area> tags and attributes look like the following: <map name=“jukebox”> <area shape=“rect” coords=“101,113, 165,134” href=“/music/classics.html” alt=“Classical Music and Composers” /> <area shape=“rect” coords=“101,139, 165,159” href=“/music/country.html” alt=“Country and Folk Music” /> <area shape=“rect” coords=“101,163, 165,183” href=“/music/rockpop.html” alt=“Rock and Pop from 50’s On” /> <area shape=“poly” coords=“175,152, 203,118, 220,118, 247,152, 237,153, 237,181, 186,181, 186,153” href=“code/music/home.html” alt=“Home Page for Music Section” /> <area shape=“rect” coords=“259,113, 323,134” href=“/music/swing.html” alt=“Swing and Big Band Music” /> <area shape=“rect” coords=“259,139, 323,159” href=“/music/jazz.html” alt=“Jazz and Free Style” /> <area shape=“rect” coords=“259,163, 323,183” href=“/music/gospel.html” alt=“Gospel and Inspirational Music” /> , , Download from www.wowebook.com ptg <area shape=“circle” coords=“379,152, 21” href=“/music/help.html” alt=“Help” /> </map> The <img> tag that refers to the map coordinates uses usemap, as follows: <img src=“jukebox.gif” usemap=“#jukebox”> Finally, put the whole thing together and test it. Here’s a sample HTML file for The Really Cool Music Page with a client-side imagemap, which contains both the <map> tag and the image that uses it: Input ▼ <!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “http://www.w3.org/TR/xhtml1/DTD/transitional.dtd”> <html> <head> <title>The Really Cool Music Page</title> </head> <body> <div align=“center”> <h1>The Really Cool Music Page</h1> <p>Select the type of music you want to hear.<br /> You’ll go to a list of songs that you can select from.</p> <p> <img src=“jukebox.gif” alt=“Juke Box” usemap=“#jukebox” /> <map name=“jukebox”> <area shape=“rect” coords=“101,113, 165,134” href=“/music/classics.html” alt=“Classical Music and Composers” /> <area shape=“rect” coords=“101,139, 165,159” href=“/music/country.html” alt=“Country and Folk Music” /> <area shape=“rect” coords=“101,163, 165,183” href=“/music/rockpop.html” alt=“Rock and Pop from 50’s On” /> <area shape=“poly” coords=“175,152, 203,118, 220,118, 247,152, 237,153, 237,181, 186,181, 186,153” href=“code/music/home.html” alt=“Home Page for Music Section” /> <area shape=“rect” coords=“259,113, 323,134” href=“/music/swing.html” alt=“Swing and Big Band Music” /> <area shape=“rect” coords=“259,139, 323,159” href=“/music/jazz.html” alt=“Jazz and Free Style” /> <area shape=“rect” coords=“259,163, 323,183” What Is an Imagemap? 253 9 , , Download from www.wowebook.com ptg href=“/music/gospel.html” alt=“Gospel and Inspirational Music” /> <area shape=“circle” coords=“379,152, 21” href=“/music/help.html” alt=“Help” /> </map></p> <p> <a href=“code/music/home.html”>Home</a> | <a href=“code/music/classics.html”>Classics</a> | <a href=“code/music/country.html”>Country</a> | <a href=“code/music/rockpop.html”>Rock/Pop</a> | <a href=“code/music/swing.html”>Swing</a> | <a href=“code/music/jazz.html”>Jazz</a> | <a href=“code/music/gospel.html”>Gospel</a> | <a href=“code/music/help.html”>Help</a> </p> </div> </body> </html> Figure 9.32 shows the imagemap in a browser. 254 LESSON 9: Adding Images, Color, and Backgrounds , Output . FIGURE 9.32 The finished Really Cool Music Page with client-side imagemap. ▲ Image Etiquette There are great images on sites all over the Web: cool icons, great photographs, excellent line art, and plenty of other graphics, too. You might feel the temptation to link directly to these images and include them on your own pages, or to save them to disk and then use them. There are a number of reasons why it’s wrong to do so. Download from www.wowebook.com ptg First, if you’re linking directly to images on another site, you’re stealing bandwidth from that site. Every time someone requests your page, they’ll also be issuing a request to the site where the image is posted and downloading the image from there. If you get a lot of traffic, you can cause problems for the remote site. The second reason is actually a problem regardless of how you use images from other sites. If you don’t have permission to use an image on your site, you’re violating the rights of the image’s creator. Copyright law protects creative work from use without per- mission, and it’s granted to every creative work automatically. The best course of action is to create your own images or look for images that are explic- itly offered for free use by their creators. Even if images are made available for your use, you should download them and store them with your web pages rather than linking to them directly. Doing so prevents you from abusing the bandwidth of the person provid- ing the images. Summary In this lesson you learned to place images on your web pages. Those images are nor- mally in GIF, JPEG, or PNG format and should be small enough that they can be down- loaded quickly over a slow link. You also learned that the HTML tag <img> enables you to put an image on a web page either inline with text or on a line by itself. The <img> tag has three primary attributes supported in standard HTML: src The location and filename of the image to include align How to position the image vertically with its surrounding text. align can have one of three values: top, middle,or bottom (deprecated from HTML5 in favor of style sheets). alt A text string to substitute for the image in text-only browsers You can include images inside a link tag (<a>) to treat them as links. In addition to the standard attributes, several other attributes to the <img> tag provide greater control over images and layout on web pages. You learned how to use these HTML 3.2 attributes in this lesson, but they have been removed from HTML5 in favor of style sheets. They include the following: align=“left” Places the image against the appropriate margin, align=“right”, allowing all the following text to flow into the space alongside the image. clear An extension to <br> that enables you to stop wrapping text alongside an image. clear can have three values: left, right, and all. Summary 255 9 Download from www.wowebook.com . 10 1 ,11 3 ,16 5 ,13 4 2 rect music/country .html 10 1 ,13 9 ,16 5 ,15 9 3 rect music/rockpop .html 10 1 ,16 3 ,16 5 ,18 3 4 poly music/home .html 17 5 ,15 2,203 ,11 8 220 ,11 8,247 ,15 2 237 ,15 3,237 ,18 1 18 6 ,18 1 ,18 6 ,15 3 , . coords= 10 1 ,16 3, 16 5 ,18 3” href=“/music/rockpop .html alt=“Rock and Pop from 50’s On” /> <area shape=“poly” coords= 17 5 ,15 2, 203 ,11 8, 220 ,11 8, 247 ,15 2, 237 ,15 3, 237 ,18 1, 18 6 ,18 1, 18 6 ,15 3” href=“code/music/home .html alt=“Home. coords= 10 1 ,16 3, 16 5 ,18 3” href=“/music/rockpop .html alt=“Rock and Pop from 50’s On” /> <area shape=“poly” coords= 17 5 ,15 2, 203 ,11 8, 220 ,11 8, 247 ,15 2, 237 ,15 3, 237 ,18 1, 18 6 ,18 1, 18 6 ,15 3” href=“code/music/home .html alt=“Home