javascript - How to get the current, "real", background image size, when background-size is cover? -


this might have been asked before , tried answer given in thread: how dimensions background image when background-size set contain?

but in case, background-size set cover, instead of contain.

the background size 1920x1080. have div-element scales width , height 100%, meanwhile background-image if said div set cover.

1920 / 1080 gives ratio of 1.7, whenever browser widow scaled div's width/height ration on or under 1.7 aka. not in correct ratio - things break. need way calculate size of background image correctly set things up.

edit: here example jsfiddle of situation: https://jsfiddle.net/ahvonenj/35pbovmz/

if resize result area, can see result area has width , height, 400x600. however, 400 width , 600 height incorrect calculations. need know size of background image is. notice how background keeps ratio leaving of image out.

the result area width , height correct when result area width/height ratio of background image, 1.7 in case.

edit 2: working: https://jsfiddle.net/ahvonenj/35pbovmz/

i found solution myself. here nice jsfiddle visualization, calculate container size , actual background image size separately.

you can resize image container (red border) dragging bottom right corner , see how container size changes separately actual background size: https://jsfiddle.net/ahvonenj/o76k5jbx/

$(document).ready(function() {     var fullhdwidth = 1920;     var fullhdheight = 1080;     var fullhdratio = fullhdwidth / fullhdheight; // 1.7      $('#wrapper').resize(function()     {         var containerwidth = $(this).width();         var containerheight = $(this).height();         var containerratio = containerwidth / containerheight;         var realwidth = null;         var realheight = null;          console.log(containerwidth, containerheight, containerratio);          if(containerratio > fullhdratio)         {             realwidth = containerwidth;             realheight = containerwidth/fullhdratio;         }         else         {             realwidth = containerheight*fullhdratio;             realheight = containerheight;         }        }); });

note: using this small library detect size changes on container div element, jquery's resize handler can bound window object.


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