Sass/Compass - Convert Hex, RGB, or Named Color to RGBA

问题

This may be Compass 101, but has anyone written a mixin which sets the alpha value of a color? Ideally, I would like the mixin to take any form of color definition, and apply transparency:

@include set-alpha( red, 0.5 );          //prints rgba(255, 0, 0, 0.5);
@include set-alpha( #ff0000, 0.5 );      //prints rgba(255, 0, 0, 0.5);
@include set-alpha( rgb(255,0,0), 0.5 ); //prints rgba(255, 0, 0, 0.5);

回答1:

Use the rgba function built into Sass

Sets the opacity of a color.

Examples:

rgba(#102030, 0.5) => rgba(16, 32, 48, 0.5)
rgba(blue, 0.2) => rgba(0, 0, 255, 0.2)

Parameters:
(Color) color
(Number) alpha — A number between 0 and 1

Returns:
(Color)

Code:

rgba(#ff0000, 0.5); // Output is rgba(255,0,0,0.5);

回答2:

I use the rgbapng compass plugin

rgbapng is a Compass plugin for providing cross-browser* compatible RGBA support. It works by creating single pixel alpha-transparent PNGs on the fly for browsers that don't support RGBA. It uses the pure Ruby ChunkyPNG library resulting in hassle-free installation and deployment.

Install

gem install compass-rgbapng

Usage

@include rgba-background(rgba(0,0,0,0.75));

Compiles to:

background: url('/images/rgbapng/000000bf.png?1282127952');
background: rgba(0, 0, 0, 0.75);

回答3:

The rgba function doesn't work on color with no transparency, it returns an hex again. After all, it's not meant to transform hex to rgba, we're just making profit out of hex doesn't allow alpha (yet).

rgba(#fff, 1) // returns #fff

So, I made al little functions that buils the rgb string. I don't need to deal with transparencies for now.

@function toRGB ($color) {
    @return "rgb(" + red($color) + ", " + green($color) + ", " + blue($color)+ ")";
}

回答4:

There's also ie-hex-str() for IE's ##AARRGGBB format:

filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#{ie-hex-str(#fdfdfd)}', endColorstr='#{ie-hex-str(#f6f6f6)}',GradientType=0); /* IE6-9 */