A mixin to resize a (rasterized pixel type) background-image using the CSS background-size property

bgSpriteFit_mixins.less

/*
* BACKGROUND-IMAGE SPRITE FIT
*
* This mixin resize a background-image via the background-size property.
* Requirements:
* * icon ratio 1:1 (square shape),
* * the first & second var are strings, all the others are digits ONLY,
* * don't put the 'px', only value as digit!
*
* -----------------------------------------------------------------
* DATA EXAMPLE FOR REFERENCE
*
* 1) @bgColor:                     transparent; //default
* 2) @bgImg_url:                   '/img/sprite/btn-50x50-sprite.png';
*
* // icon sizes:
* 3) @spriteIco_pxSize_original:   50;
* 4) @spriteIco_pxRequired_value:  34;
*
* // image-sprite size:
* 5) @imgFile_pxSize_w:            300;
* 6) @imgFile_pxSize_h:            150;
*
* // icon position within the image-sprite:
* 7) @bgImg_pxPosition_x:          200;
* 8) @bgImg_pxPosition_y:          50;
* 9) @bgImg_pxPosition_y_hover:    100;
*
*/
.bgSpriteFit(@bgColor:transparent, @bgImg_url, @spriteIco_pxSize_original, @spriteIco_pxRequired_value, @imgFile_pxSize_w, @imgFile_pxSize_h, @bgImg_pxPosition_x:0, @bgImg_pxPosition_y:0, @bgImg_pxPosition_y_hover:0) when (isnumber(@spriteIco_pxSize_original)) and (isnumber(@spriteIco_pxRequired_value)) and (isstring(@bgImg_url)) and (isnumber(@imgFile_pxSize_w)) and (isnumber(@imgFile_pxSize_h)) and (isnumber(@bgImg_pxPosition_x)) and (isnumber(@bgImg_pxPosition_y)) and (isnumber(@bgImg_pxPosition_y_hover)) {
 
    // calculate ratio
    @spriteResize_ratio_value:          floor(((100/@spriteIco_pxSize_original)*(@spriteIco_pxRequired_value))); //calcul
    @spriteResize_ratio:                ((@spriteResize_ratio_value)/100); //pourcentage in decimals. ex: 75% = 0.75
    //turn it in a pourcentage string
    @spriteResize:                      ~'@{spriteResize_ratio_value}%'; //pourcentage string interpolation
    // calculate background-size height value
    @imgFile_pxResized_h_value:         floor(((@imgFile_pxSize_h)*(@spriteResize_ratio)));
    //turn it in a pixel string
    @imgFile_pxResized_h:               ~'@{imgFile_pxResized_h_value}px'; //pixel string interpolation
    //turn pxRequired in pixel string
    @spriteIco_pxResized :              ~'@{spriteIco_pxRequired_value}px'; //pixel string interpolation
 
    // re-calculate background-position after applying resized value
    @resized_bgImg_pxPosition_x_value:  floor(((@bgImg_pxPosition_x)*(@spriteResize_ratio))); //calcul (ex: 250px * 68% = 170)
    @resized_bgImg_pxPosition_y_value:  floor(((@bgImg_pxPosition_y)*(@spriteResize_ratio)));  //calcul (ex: 50px * 68% = 34)
    @resized_bgImg_pxPosition_y_hover_value: floor(((@bgImg_pxPosition_y_hover)*(@spriteResize_ratio)));  //calcul (ex: 100px * 68% = 68)
    //turn them in pixel strings
    @resized_bgImg_pxPosition_x:        ~'@{resized_bgImg_pxPosition_x_value}px'; //pixel string interpolation
    @resized_bgImg_pxPosition_y:        ~'@{resized_bgImg_pxPosition_y_value}px'; //pixel string interpolation
    @resized_bgImg_pxPosition_y_hover:  ~'@{resized_bgImg_pxPosition_y_hover_value}px'; //pixel string interpolation
 
    /*
     * render
     */
    width: @spriteIco_pxResized;
    height: @spriteIco_pxResized;
    background: @bgColor url(@bgImg_url) no-repeat ~'-@{resized_bgImg_pxPosition_x}' ~'-@{resized_bgImg_pxPosition_y}';
    background-size: auto (@imgFile_pxResized_h);
    // hover state
    &:hover {
        background-position: ~'-@{resized_bgImg_pxPosition_x}' ~'-@{resized_bgImg_pxPosition_y_hover}';
    }
}