国产99久久精品_欧美日本韩国一区二区_激情小说综合网_欧美一级二级视频_午夜av电影_日本久久精品视频

最新文章專題視頻專題問答1問答10問答100問答1000問答2000關鍵字專題1關鍵字專題50關鍵字專題500關鍵字專題1500TAG最新視頻文章推薦1 推薦3 推薦5 推薦7 推薦9 推薦11 推薦13 推薦15 推薦17 推薦19 推薦21 推薦23 推薦25 推薦27 推薦29 推薦31 推薦33 推薦35 推薦37視頻文章20視頻文章30視頻文章40視頻文章50視頻文章60 視頻文章70視頻文章80視頻文章90視頻文章100視頻文章120視頻文章140 視頻2關鍵字專題關鍵字專題tag2tag3文章專題文章專題2文章索引1文章索引2文章索引3文章索引4文章索引5123456789101112131415文章專題3
問答文章1 問答文章501 問答文章1001 問答文章1501 問答文章2001 問答文章2501 問答文章3001 問答文章3501 問答文章4001 問答文章4501 問答文章5001 問答文章5501 問答文章6001 問答文章6501 問答文章7001 問答文章7501 問答文章8001 問答文章8501 問答文章9001 問答文章9501
當前位置: 首頁 - 科技 - 知識百科 - 正文

Cross-BrowserVariableOpacitywithPNG_經驗交流

來源:懂視網 責編:小采 時間:2020-11-27 18:54:41
文檔

Cross-BrowserVariableOpacitywithPNG_經驗交流

Cross-BrowserVariableOpacitywithPNG_經驗交流:Periodically, someone tells me about the magic of PNG, how it's the ideal image format for the web, and that someday we'll all be using it on our sites instead of GIF. People have been saying this for years, and by now most of us have stopp
推薦度:
導讀Cross-BrowserVariableOpacitywithPNG_經驗交流:Periodically, someone tells me about the magic of PNG, how it's the ideal image format for the web, and that someday we'll all be using it on our sites instead of GIF. People have been saying this for years, and by now most of us have stopp
Periodically, someone tells me about the magic of PNG, how it's the ideal image format for the web, and that someday we'll all be using it on our sites instead of GIF. People have been saying this for years, and by now most of us have stopped listening. Sadly, flaky browser support has made PNG impractical for almost everything; but now, with a few simple workarounds, we can finally put one of its most compelling features to use.

PNG? What?

The Portable Network Graphics, or PNG (pronounced “ping”), image format has been around since 1995, having cropped up during the now long-forgotten GIF scare, when Compuserve and Unisys announced they would begin charging royalties for the use of the GIF image format.

To provide GIF support in their applications, software makers like Adobe and Macromedia must pay royalty fees – fees which are passed down to the end user in the selling cost of the software.

When PNG appeared on the scene, web designers were ready to make the switch to the free, superior format and shun GIF forever. But over time, browsers continually failed to support PNG, and eventually most people started to forget about it. Today, nearly everyone still uses GIF habitually.

Which is a shame, because PNG makes GIF look pretty pathetic: it supports gamma correction, (sometimes) smaller file sizes, loss-less compression, up to 48-bit color, and, best of all, true alpha transparency.

To get why alpha transparency is a big deal, we must first understand one of the most annoying limitations of GIF.

Binary Transparency: the Scourge of GIF

When it comes to transparency, GIF doesn't cut it. Whereas PNG supports alpha transparency, GIF only supports binary transparency, which is a big limitation and has a couple of important implications.

For one, a GIF image can either use no transparent colors at all or have one color that's completely transparent – there are no degrees of transparency.

And if a complex GIF does contain a transparent color, the background color of the web page must match the transparent color, or else the anti-aliased area around the transparent color will be surrounded by ugly haloing and fringing. If you've spent more than five minutes as a web designer, you know what I'm talking about.

The result is that any anti-aliased transparent GIF is inextricably tied to the background color of the web page on which it lives. If you ever decide to change that color, you must also change the GIF.

Miraculously, PNG doesn't behave that way. A PNG can be transparent in varying degrees – in other words, it can be of variable opacity. And a transparent PNG is background-independent: it can live on any background color or image. Say you want your navigation on monkeys-run-amuck.com to be 65% opaque so you can see through it to your orangutan background image. You can do that. A transparent anti-aliased “Gorillas, Chimps, Gibbons, et al” title that can sit on top of any background color or image? You can do that, too.

So What About Browser Support?

By now, of course, we'd all be up to our ears in PNGs if browsers supported them reliably. But seven years after the format's inception, you still can't slap a PNG onto a web page like you can a GIF or JPG. It's disgraceful, but not as bad as it sounds.

It turns out that most of the latest versions of the major browsers fully support alpha transparency with PNG – namely, Netscape 6, Opera 6, and recently-released Mozilla 1, all on Windows; and, for the Mac, Internet Explorer 5, Netscape 6, Opera 5, Mozilla 1, OmniWeb 3.1, and ICab 1.9. Incredibly, PNG even works on Opera 6 for Linux, on WebTV, and on Sega Dreamcast.

Now, what's missing from that list?

IE5.5+/Win, bless its heart, will, in fact, display a PNG, but it doesn't natively support alpha transparency. In IE5.5+/Win, the transparent area of your PNG will display at 100% opacity – that is, it won't be transparent at all.

Bugger. So what do we do now?

Proprietary Code-o-Rama: the AlphaImageLoader Filter

IE4+/Win supports a variety of non-standard, largely ridiculous visual filters that you can apply to any image's style. You can, for instance, fade in an image with a gradient wipe, or make it stretch from nothing to full size, or even make it swipe into place circularly, like a scene change in Star Wars.

A non-pointless gem among these is the AlphaImageLoader filter, which is supported in IE5.5+/Win. When used to display a PNG, it allows for full alpha transparency support. All you have to do is this:

»
(src='myimage.png',sizingMethod='scale');">

(Line wraps are marked ». –Ed.)

And you're in business. Perfect alpha transparency. This code works great, with only the small drawback that it's not part of any accepted web standard, and no other browser on the planet understands it.

Serving up PNGs with JavaScript

So the trick is to determine the user's browser and serve up the images appropriately: if IE5.5+/Win, then we use AlphaImageLoader; if a browser with native PNG support, then we display PNGs the normal way; if anything else, then we display alternate GIFs, because we can't be sure that a PNG will display correctly or at all.

Using a slightly tweaked version of Chris Nott's Browser Detect Lite, we set some global variables to this effect that we can use later on.

// if IE5.5+ on Win32, then display PNGs with AlphaImageLoader
if ((browser.isIE55 || browser.isIE6up) && browser.isWin32) {
	var pngAlpha = true;
// else, if the browser can display PNGs normally, then do that
} else if ((browser.isGecko) |»
| (browser.isIE5up && browser.isMac) |»
| (browser.isOpera && browser.isWin »
	&& browser.versionMajor >= 6) |»
| (browser.isOpera && browser.isUnix »
&& browser.versionMajor >= 6) |»
| (browser.isOpera && browser.isMac »
	&& browser.versionMajor >= 5) |»
| (browser.isOmniweb && »
	browser.versionMinor >= 3.1) |»
| (browser.isIcab && »
	browser.versionMinor >= 1.9) |»
| (browser.isWebtv) |»
| (browser.isDreamcast)) {
	var pngNormal = true;
}

(Note for the faint of heart: complete source code for all the examples we cover is available at the end of the article.)

Tactic 1: Quick and Dirty with document.writes

The simplest, most reliable way to spit out PNGs is using inline document.writes based on the above detection. So we use a function like this:

function od_displayImage(strId, strPath, intWidth, »
	intHeight, strClass, strAlt) {	
 if (pngAlpha) {
 document.write('»
	width:'+intWidth+'px;»
 filter:progid:DXImageTransform.Microsoft.AlphaImageLoader»
 (src=\'https://www.gxlcms.com/'+strPath+'.png\', sizingMethod=\'scale\')" »
	id="'+strId+'" class="'+strClass+'">');
	} else if (pngNormal) {
 document.write(''+strAlt+'');
	} else {
 document.write(''+strAlt+'');
	}
}

Now we can call the od_displayImage function from anywhere on the page. Any JavaScript-capable browser will display an image, and, if we want to be really careful, we can accompany each call with a

It's a time-tested method, but what if we want more control over our PNGs?

Tactic 2: the Beauty & Majesty of Objects

When I told the programmer in the office next door that I was writing this article, he took one look at my code, glowered at me, and said, “Fool. Where's the abstraction? You need to use objects.”

So now we have a JavaScript object to display PNGs. Here's how we use it:


聲明:本網頁內容旨在傳播知識,若有侵權等問題請及時與本網聯系,我們將在第一時間刪除處理。TEL:177 7030 7066 E-MAIL:11247931@qq.com

文檔

Cross-BrowserVariableOpacitywithPNG_經驗交流

Cross-BrowserVariableOpacitywithPNG_經驗交流:Periodically, someone tells me about the magic of PNG, how it's the ideal image format for the web, and that someday we'll all be using it on our sites instead of GIF. People have been saying this for years, and by now most of us have stopp
推薦度:
標簽: png browser with
  • 熱門焦點

最新推薦

猜你喜歡

熱門推薦

專題
Top 主站蜘蛛池模板: 高清国产美女一级a毛片 | 欧美性xxxbbb| 国产成人综合久久精品下载 | 亚洲色图欧美在线 | 日韩欧美制服 | 日本全黄 | 日韩欧美片 | 免费高清欧美大片在线观看 | 亚洲国产视频网 | 性刺激欧美三级在线现看中文 | 亚洲国产精品嫩草影院久久 | 日本a级片免费观看 | 热久久中文字幕 | 亚洲欧美日韩成人 | 日韩在线欧美高清一区 | 国产一区二区三区在线视频 | 国产视频高清在线观看 | 国产精品亚洲一区二区三区 | 国产成人精品久久一区二区小说 | 久久99久久精品国产99热 | 日韩精品第三页 | 中文字幕日韩一区二区三区不卡 | 欧美日韩精品国产一区二区 | 亚洲欧美字幕 | 精品一区二区久久久久久久网精 | 国产一区精品在线观看 | 欧美日韩一 | 国产一区二区在线看 | 久久精品91 | 精品视频在线观看一区二区三区 | 国产精品原创视频 | 偷拍第一页| 视频一区二区三区欧美日韩 | 亚洲欧美中文日韩综合 | 亚洲综合视频 | 人人添人人澡人人澡人人人爽 | 欧美日韩v | 午夜日韩久久影院 | 欧美日韩国产成人精品 | 欧美成人精品高清在线播放 | 欧美视频在线观看免费 |