{"rowid": 165, "title": "Transparent PNGs in Internet Explorer 6", "contents": "Newer breeds of browser such as Firefox and Safari have offered support for PNG images with full alpha channel transparency for a few years. With the use of hacks, support has been available in Internet Explorer 5.5 and 6, but the hacks are non-ideal and have been tricky to use. With IE7 winning masses of users from earlier versions over the last year, full PNG alpha-channel transparency is becoming more of a reality for day-to-day use.\n\nHowever, there are still numbers of IE6 users out there who we can\u2019t leave out in the cold this Christmas, so in this article I\u2019m going to look what we can do to support IE6 users whilst taking full advantage of transparency for the majority of a site\u2019s visitors.\n\nSo what\u2019s alpha channel transparency?\n\nCast your minds back to the Ghost of Christmas Past, the humble GIF. Images in GIF format offer transparency, but that transparency is either on or off for any given pixel. Each pixel\u2019s either fully transparent, or a solid colour. In GIF, transparency is effectively just a special colour you can chose for a pixel.\n\nThe PNG format tackles the problem rather differently. As well as having any colour you chose, each pixel also carries a separate channel of information detailing how transparent it is. This alpha channel enables a pixel to be fully transparent, fully opaque, or critically, any step in between.\n\nThis enables designers to produce images that can have, for example, soft edges without any of the \u2018halo effect\u2019 traditionally associated with GIF transparency. If you\u2019ve ever worked on a site that has different colour schemes and therefore requires multiple versions of each graphic against a different colour, you\u2019ll immediately see the benefit. \n\nWhat\u2019s perhaps more interesting than that, however, is the extra creative freedom this gives designers in creating beautiful sites that can remain web-like in their ability to adjust, scale and reflow.\n\nThe Internet Explorer problem\n\nUp until IE7, there has been no fully native support for PNG alpha channel transparency in Internet Explorer. However, since IE5.5 there has been some support in the form of proprietary filter called the AlphaImageLoader. Internet Explorer filters can be applied directly in your CSS (for both inline and background images), or by setting the same CSS property with JavaScript. \n\nCSS:\n\nimg {\n\tfilter: progid:DXImageTransform.Microsoft.AlphaImageLoader(...);\n}\n\nJavaScript:\n\nimg.style.filter = \"progid:DXImageTransform.Microsoft.AlphaImageLoader(...)\";\n\nThat may sound like a problem solved, but all is not as it may appear. Firstly, as you may realise, there\u2019s no CSS property called filter in the W3C CSS spec. It\u2019s a proprietary extension added by Microsoft that could potentially cause other browsers to reject your entire CSS rule. \n\nSecondly, AlphaImageLoader does not magically add full PNG transparency support so that a PNG in the page will just start working. Instead, when applied to an element in the page, it draws a new rendering surface in the same space that element occupies and loads a PNG into it. If that sounds weird, it\u2019s because that\u2019s precisely what it is. However, by and large the result is that PNGs with an alpha channel can be accommodated.\n\nThe pitfalls\n\nSo, whilst support for PNG transparency in IE5.5 and 6 is possible, it\u2019s not without its problems.\n\nBackground images cannot be positioned or repeated\n\nThe AlphaImageLoader does work for background images, but only for the simplest of cases. If your design requires the image to be tiled (background-repeat) or positioned (background-position) you\u2019re out of luck. The AlphaImageLoader allows you to set a sizingMethod to either crop the image (if necessary) or to scale it to fit. Not massively useful, but something at least.\n\nDelayed loading and resource use\n\nThe AlphaImageLoader can be quite slow to load, and appears to consume more resources than a standard image when applied. Typically, you\u2019d need to add thousands of GIFs or JPEGs to a page before you saw any noticeable impact on the browser, but with the AlphaImageLoader filter applied Internet Explorer can become sluggish after just a handful of alpha channel PNGs.\n\nThe other noticeable effect is that as more instances of the AlphaImageLoader are applied, the longer it takes to render the PNGs with their transparency. The user sees the PNG load in its original non-supported state (with black or grey areas where transparency should be) before one by one the filter kicks in and makes them properly transparent.\n\nBoth the issue of sluggish behaviour and delayed load only really manifest themselves with volume and size of image. Use just a couple of instances and it\u2019s fine, but be careful adding more than five or six. As ever, test, test, test.\n\nLinks become unclickable, forms unfocusable \n\nThis is a big one. There\u2019s a bug/weirdness with AlphaImageLoader that sometimes prevents interaction with links and forms when a PNG background image is used. This is sometimes reported as a z-index issue, but I don\u2019t believe it is. Rather, it\u2019s an artefact of that weird way the filter gets applied to the document almost outside of the normal render process. \n\nOften this can be solved by giving the links or form elements hasLayout using position: relative; where possible. However, this doesn\u2019t always work and the non-interaction problem cannot always be solved. You may find yourself having to go back to the drawing board.\n\nSidestepping the danger zones\n\nFrankly, it\u2019s pretty bad news if you design a site, have that design signed off by your client, build it and then find out only at the end (because you don\u2019t know what might trigger a problem) that your search field can\u2019t be focused in IE6. That\u2019s an absolute nightmare, and whilst it\u2019s not likely to happen, it\u2019s possible that it might. It\u2019s happened to me. So what can you do?\n\nThe best approach I\u2019ve found to this scenario is\n\n\n\tIsolate the PNG or PNGs that are causing the problem. Step through the PNGs in your page, commenting them out one by one and retesting. Typically it\u2019ll be the nearest PNG to the problem, so try there first. Keep going until you can click your links or focus your form fields.\n\tThis is where you really need luck on your side, because you\u2019re going to have to fake it. This will depend on the design of the site, but some way or other create a replacement GIF or JPEG image that will give you an acceptable result. Then use conditional comments to serve that image to only users of IE older than version 7.\n\n\nA hack, you say? Well, you started it chum.\n\nApplying AlphaImageLoader\n\nBecause the filter property is invalid CSS, the safest pragmatic approach is to apply it selectively with JavaScript for only Internet Explorer versions 5.5 and 6. This helps ensure that by default you\u2019re serving standard CSS to browsers that support both the CSS and PNG standards correct, and then selectively patching up only the browsers that need it. \n\nSeveral years ago, Aaron Boodman wrote and released a script called sleight for doing just that. However, sleight dealt only with images in the page, and not background images applied with CSS. Building on top of Aaron\u2019s work, I hacked sleight and came up with bgsleight for applying the filter to background images instead. That was in 2003, and over the years I\u2019ve made a couple of improvements here and there to keep it ticking over and to resolve conflicts between sleight and bgsleight when used together. However, with alpha channel PNGs becoming much more widespread, it\u2019s time for a new version.\n\nIntroducing SuperSleight\n\nSuperSleight adds a number of new and useful features that have come from the day-to-day needs of working with PNGs.\n\n\n\tWorks with both inline and background images, replacing the need for both sleight and bgsleight\n\tWill automatically apply position: relative to links and form fields if they don\u2019t already have position set. (Can be disabled.)\n\tCan be run on the entire document, or just a selected part where you know the PNGs are. This is better for performance.\n\tDetects background images set to no-repeat and sets the scaleMode to crop rather than scale.\n\tCan be re-applied by any other JavaScript in the page \u2013 useful if new content has been loaded by an Ajax request.\n\n\n Download SuperSleight \n\nImplementation\n\nGetting SuperSleight running on a page is quite straightforward, you just need to link the supplied JavaScript file (or the minified version if you prefer) into your document inside conditional comments so that it is delivered to only Internet Explorer 6 or older.\n\n\n\nSupplied with the JavaScript is a simple transparent GIF file. The script replaces the existing PNG with this before re-layering the PNG over the top using AlphaImageLoaded. You can change the name or path of the image in the top of the JavaScript file, where you\u2019ll also find the option to turn off the adding of position: relative to links and fields if you don\u2019t want that.\n\nThe script is kicked off with a call to supersleight.init() at the bottom. The scope of the script can be limited to just one part of the page by passing an ID of an element to supersleight.limitTo(). And that\u2019s all there is to it.\n\nUpdate March 2008: a version of this script as a jQuery plugin is also now available.", "year": "2007", "author": "Drew McLellan", "author_slug": "drewmclellan", "published": "2007-12-01T00:00:00+00:00", "url": "https://24ways.org/2007/supersleight-transparent-png-in-ie6/", "topic": "code"} {"rowid": 163, "title": "Get To Grips with Slippy Maps", "contents": "Online mapping has definitely hit mainstream. Google Maps made \u2018slippy maps\u2019 popular and made it easy for any developer to quickly add a dynamic map to his or her website. You can now find maps for store locations, friends nearby, upcoming events, and embedded in blogs. \n\nIn this tutorial we\u2019ll show you how to easily add a map to your site using the Mapstraction mapping library. There are many map providers available to choose from, each with slightly different functionality, design, and terms of service. Mapstraction makes deciding which provider to use easy by allowing you to write your mapping code once, and then easily switch providers.\n\nAssemble the pieces\n\nUtilizing any of the mapping library typically consists of similar overall steps:\n\n\n\tCreate an HTML div to hold the map\n\tInclude the Javascript libraries\n\tCreate the Javascript Map element\n\tSet the initial map center and zoom level\n\tAdd markers, lines, overlays and more\n\n\nCreate the Map Div\n\nThe HTML div is where the map will actually show up on your page. It needs to have a unique id, because we\u2019ll refer to that later to actually put the map here. This also lets you have multiple maps on a page, by creating individual divs and Javascript map elements. The size of the div also sets the height and width of the map. You set the size using CSS, either inline with the element, or via a CSS reference to the element id or class. For this example, we\u2019ll use inline styling.\n\n
\n\nInclude Javascript libraries\n\nA mapping library is like any Javascript library. You need to include the library in your page before you use the methods of that library. For our tutorial, we\u2019ll need to include at least two libraries: Mapstraction, and the mapping API(s) we want to display. Our first example we\u2019ll use the ubiquitous Google Maps library. However, you can just as easily include Yahoo, MapQuest, or any of the other supported libraries.\n\nAnother important aspect of the mapping libraries is that many of them require an API key. You will need to agree to the terms of service, and get an API key these.\n\n\n\n\nCreate the Map\n\nGreat, we\u2019ve now put in all the pieces we need to start actually creating our map. This is as simple as creating a new Mapstraction object with the id of the HTML div we created earlier, and the name of the mapping provider we want to use for this map. \n\nWith several of the mapping libraries you will need to set the map center and zoom level before the map will appear. The map centering actually triggers the initialization of the map. \n\nvar mapstraction = new Mapstraction('map','google');\nvar myPoint = new LatLonPoint(37.404,-122.008);\nmapstraction.setCenterAndZoom(myPoint, 10);\n\nA note about zoom levels. The setCenterAndZoom function takes two parameters, the center as a LatLonPoint, and a zoom level that has been defined by mapping libraries. The current usage is for zoom level 1 to be \u201czoomed out\u201d, or view the entire earth \u2013 and increasing the zoom level as you zoom in. Typically 17 is the maximum zoom, which is about the size of a house. \n\nDifferent mapping providers have different quality of zoomed in maps over different parts of the world. This is a perfect reason why using a library like Mapstraction is very useful, because you can quickly change mapping providers to accommodate users in areas that have bad coverage with some maps. \n\nTo switch providers, you just need to include the Javascript library, and then change the second parameter in the Mapstraction creation. Or, you can call the switch method to dynamically switch the provider.\n\nSo for Yahoo Maps (demo):\n\nvar mapstraction = new Mapstraction('map','yahoo');\n\nor Microsoft Maps (demo):\n\nvar mapstraction = new Mapstraction('map','microsoft');\n\nwant a 3D globe in your browser? try FreeEarth (demo):\n\nvar mapstraction = new Mapstraction('map','freeearth');\n\nor even OpenStreetMap (free your data!) (demo):\n\nvar mapstraction = new Mapstraction('map','openstreetmap');\n\nVisit the Mapstraction multiple map demo page for an example of how easy it is to have many maps on your page, each with a different provider. \n\nAdding Markers\n\nWhile adding your first map is fun, and you can probably spend hours just sliding around, the point of adding a map to your site is usually to show the location of something. So now you want to add some markers. There are a couple of ways to add to your map.\n\nThe simplest is directly creating markers. You could either hard code this into a rather static page, or dynamically generate these using whatever tools your site is built on.\n\nvar marker = new Marker( new LatLonPoint(37.404,-122.008) );\nmarker.setInfoBubble(\"It's easy to add maps to your site\");\nmapstraction.addMarker( marker );\n\nThere is a lot more you can do with markers, including changing the icon, adding timestamps, automatically opening the bubble, or making them draggable. \n\nWhile it is straight-forward to create markers one by one, there is a much easier way to create a large set of markers. And chances are, you can make it very easy by extending some data you already are sharing: RSS. \n\nSpecifically, using GeoRSS you can easily add a large set of markers directly to a map. GeoRSS is a community built standard (like Microformats) that added geographic markup to RSS and Atom entries. It\u2019s as simple as addingI wish Google could find my keys
\n\nCSS:\n\na:link:after,\na:visited:after,\na:hover:after,\na:active:after {\n\tcontent: \" <\" attr(href) \"> \";\n}\n\nBut this is not perfect, in the above example the content of the href is just naively plonked after the link text:\n\nI wish Google12b Meeting House Lane
\n\t\tBrighton, UK
\n\t\tBN1 1HB
\n\tTelephone: +44 (0)1273 323 008
\n\tE-mail: info@riddleandfinns.co.uk
\n22-23 Sydney Street
\n\t\tBrighton, UK
\n\t\tBN1 4EN
\n\tTelephone: +44 (0)1273 687 068
\n\tLat/Lon: \n\t\t50.827917, \n\t\t-0.137764\n\t
\n