bootstrap-less-port/less/mixins/_image.less

A Less port of Bootstrap v4

// Image Mixins
// - Responsive image
// - Retina image


// Responsive image
//
// Keep images from scaling beyond the width of their parents.

#img-fluid() {
	// Part 1: Set a maximum relative to the parent
	max-width: 100%;
	// Part 2: Override the height to auto, otherwise images will be stretched
	// when setting a width and height attribute on the img element.
	height: auto;
}


// Retina image
//
// Short retina mixin for setting background-image and -size.

#img-retina(@file-1x, @file-2x, @width-1x, @height-1x) {
	background-image: url(@file-1x);

	// Autoprefixer takes care of adding -webkit-min-device-pixel-ratio and -o-min-device-pixel-ratio,
	// but doesn't convert dppx=>dpi.
	// There's no such thing as unprefixed min-device-pixel-ratio since it's nonstandard.
	// Compatibility info: https://caniuse.com/#feat=css-media-resolution
	@media only screen and (min-resolution: 192dpi), // IE9-11 don't support dppx
		only screen and (min-resolution: 2dppx) { // Standardized
		background-image: url(@file-2x);
		background-size: @width-1x @height-1x;
	}
	#deprecate("`#img-retina()`", "v4.3.0", "v5");
}