Why Does My Full-Screen Background Image Jump in Mobile Chrome and How Can I Fix It?

Background Image Offset Issue in Mobile Chrome

In responsive web design, it's common to use full-screen background images that resize and transition smoothly. However, developers often encounter an issue where the background jumps abruptly when the address bar in iOS Safari, Android Browser, or Chrome on Android hides upon scrolling down.

Cause of the Issue

The problem arises when using fixed-height background divs with a background-size value of "cover". As the address bar shrinks, the height of the background div changes, causing the image to readjust its size and position to cover the available area.

Solution 1: Setting #bg1 and #bg2 Height to 100vh

Attempting to set the background div height to 100vh (viewport height) would seem like an elegant solution, but iOS has a vh bug that prevents this approach from working reliably.

Solution 2: Using Javascript to Set Static Height

Since the viewport size determined by Javascript is unaffected by the URL bar, you can use Javascript to set a static height on the background divs based on the viewport size. This is not an ideal solution, but it effectively prevents the background image from resizing:

var bg = $("#bg1, #bg2");

function resizeBackground() {
    bg.height($(window).height());
}

$(window).resize(resizeBackground);
resizeBackground();

Additional Notes

It's important to note that this issue is caused by the resizing address bar in iOS and Android platforms. The latest change in these browsers prevents the URL bar from being hidden on page load using scroll tricks.

Addressing the Scroll Gap

The above script effectively prevents the background from resizing, but it can cause a noticeable gap when users scroll down. To address this, add 60px to the background height:

function resizeBackground() {
    bg.height( $(window).height() + 60);
}

This modification will prevent the gap, but it may result in the bottom 60px of the background image being hidden when the URL bar is present.

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