How to Keep Fixed Elements from Resizing During Touchscreen Zoom?

Maintaining Fixed Element Size During Touchscreen Zooming

Mobile devices equipped with touchscreens pose a unique challenge for fixed elements on web pages. When users pinch the screen to zoom in, fixed elements tend to resize along with the rest of the content, potentially obscuring underlying elements.

To prevent this behavior, we can employ a technique that calculates the current zoom factor and applies an appropriate CSS3 transform to the fixed element, ensuring it remains the same size at all times.

<code class="javascript">window.addEventListener('scroll', function(e) {
    var zoom = window.innerWidth / document.documentElement.clientWidth;
    el.style["transform"] = "scale(" + zoom + ")";
});</code>

This logic calculates the zoom factor and applies it as a scale transform. However, since the fixed element's position might become inaccurate, we adjust it using absolute positioning:

<code class="javascript">el.style.left = window.pageXOffset + 'px';
el.style.bottom = document.documentElement.clientHeight - (window.pageYOffset + window.innerHeight) + 'px';</code>

Positioning the fixed element within a 100% content height parent element and adjusting its position based on viewport dimensions ensure it stays visible at the desired location, regardless of zoom level.

Pay attention to the transform-origin property if you need to control the scaling anchor point for the fixed element. By utilizing this technique, you can create elements that maintain their size during touchscreen zoom events, enhancing the user experience on mobile devices.

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