I have a webpage where I want the user to see a new image when they put thier mouse over a certain part of the image. I used an image map.
<img src="pic.jpg" usemap="#picmap" />
<map id="picmap" name="picmap"><area shape="rect" coords ="10,20,30,40"
onMouseOver="mouse_on_write('mouse is on spot')"
onMouseOut="mouse_off('mouse is off spot')"
href="http://www....html" target="_blank" />
</map>
<p id="desc"></p>
Where in the header I defined these functions:
<script type="text/javascript">
function mouse_off(txt)
{
document.getElementById("desc").innerHTML=txt;
document.p1.src="pic.jpg";
}
function mouse_on_write(txt)
{
document.getElementById("desc").innerHTML=txt;
document.p1.src="pic2.jpg";
</script>
It works, but it is slow. When the mouse is put over the second image it takes some few seconds to appear; my temporary solution was to drastically reduce the size of the images because they were huge (at 2.5mb they switch fast now, but still not seamless). How can I make the image switching more seamless without reduction in picture quality? On second thought I realize that I could also just have both images displayed, at a small and a large scale, and on mouse over they would switch places; How would I do this? Would this reduce lag?
To preload responsive images, new attributes were recently added to the <link> element: imagesrcset and imagesizes . They are used with <link rel="preload"> and match the srcset and sizes syntax used in <img> element. This kicks off a request using the same resource selection logic that srcset and sizes will apply.
Image caching essentially means downloading an image to the local storage in the app's cache directory (or any other directory that is accessible to the app) and loading it from local storage next time the image loads.
Yes the browser will cache them, often even when your headers say otherwise.
You don't need to create any page elements, it can all be preloaded using JavaScript:
tempImg = new Image()
tempImg.src="pic2.jpg"
EDIT:
If you have a lot of images, you can use the poor-man's multi-preloader:
preloads = "red.gif,green.gif,blue.gif".split(",")
var tempImg = []
for(var x=0;x<preloads.length;x++) {
tempImg[x] = new Image()
tempImg[x].src = preloads[x]
}
Doing this with sprites is a good solution, because you don't have to wait to load the new image. Sprites work by combining the two images into one, and changing the background offset on mouseover.
You can even do with with CSS instead, for much faster results. There's a good tutorial on this here.
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