1 files changed, 127 insertions, 0 deletions

diff --git a/src/functions/colors/_apca.scss b/src/functions/colors/_apca.scss
new file mode 100644
index 0000000..d9236b2
--- /dev/null
+++ b/src/functions/colors/_apca.scss
@@ -0,0 +1,127 @@
+/* stylelint-disable scss/dollar-variable-pattern */
+/* stylelint-disable scss/at-function-pattern */
+
+@use 'sass:color';
+@use 'sass:list';
+@use 'sass:map';
+@use 'sass:math';
+
+$SA98G: (
+    mainTRC:     2.4,
+
+    sRco:        0.2126729, 
+    sGco:        0.7151522, 
+    sBco:        0.0721750,
+
+    normBG:      0.56, 
+    normTXT:     0.57,
+    revTXT:      0.62,
+    revBG:       0.65,
+
+    blkThrs:     0.022,
+    blkClmp:     1.414,
+    scaleBoW:    1.14,
+    scaleWoB:    1.14,
+    loBoWoffset: 0.027,
+    loWoBoffset: 0.027,
+    deltaYmin:   0.0005,
+    loClip:      0.0001,
+
+    mFactor:     1.94685544331710,
+    mOffsetIn:   0.03873938165714010,
+    mExpAdj:     0.2833433964208690,
+    mOffsetOut:  0.3128657958707580,
+);
+
+@function apca_sRGB_to_Y($color) {
+    @return map.get($SA98G, sRco) * math.pow(math.div(color.red($color), 255), map.get($SA98G, mainTRC)) +
+        map.get($SA98G, sGco) * math.pow(math.div(color.green($color), 255), map.get($SA98G, mainTRC)) +
+        map.get($SA98G, sBco) * math.pow(math.div(color.blue($color), 255), map.get($SA98G, mainTRC));
+}
+
+@function apca_Y_to_sRGB($y) {
+    $c: math.round(math.pow($y, math.div(1, map.get($SA98G, mainTRC))) * 255);
+    @return rgb($c, $c, $c);
+}
+
+@function apcaContrast($txtY, $bgY) {
+    $icp: 0.0 1.1;
+
+    @if math.min($txtY, $bgY) < list.nth($icp, 1) or math.max($txtY, $bgY) > list.nth($icp, 2) {
+        @return 0;
+    }
+
+    @if $txtY <= map.get($SA98G, blkThrs) {
+        $txtY: $txtY + math.pow(map.get($SA98G, blkThrs) - $txtY, map.get($SA98G, blkClmp));
+    }
+    @if $bgY <= map.get($SA98G, blkThrs) {
+        $bgY: $bgY + math.pow(map.get($SA98G, blkThrs) - $bgY, map.get($SA98G, blkClmp));
+    }
+
+    @if math.abs($bgY - $txtY) < map.get($SA98G, deltaYmin) {
+        @return 0;
+    }
+
+    $outputContrast: 0;
+
+    @if $bgY > $txtY {
+        $SAPC: map.get($SA98G, scaleBoW) * (math.pow($bgY, map.get($SA98G, normBG)) - math.pow($txtY, map.get($SA98G, normTXT)));
+        
+        @if $SAPC >= map.get($SA98G, loClip) {
+            $outputContrast: $SAPC - map.get($SA98G, loBoWoffset);
+        }
+    } @else {
+        $SAPC: map.get($SA98G, scaleWoB) * (math.pow($bgY, map.get($SA98G, revBG)) - math.pow($txtY, map.get($SA98G, revTXT)));
+        
+        @if $SAPC <= -1 * map.get($SA98G, loClip) {
+            $outputContrast: $SAPC + map.get($SA98G, loWoBoffset);
+        }
+    }
+
+    @return $outputContrast * 100.0;
+}
+
+@function apcaReverse($contrast, $knownY, $knownType: 'bg') {
+    $unknownY:   $knownY;
+
+    $knownExp:   0;
+    $unknownExp: 0;
+
+    $scale:  map.get($SA98G, if($contrast > 0, scaleBoW, scaleWoB));
+    $offset: map.get($SA98G, if($contrast > 0, loBoWoffset, loWoBoffset));
+
+    $contrast: math.div($contrast * 0.01 + $offset, $scale);
+
+    @if $knownY <= map.get($SA98G, blkThrs) {
+        $knownY: $knownY + math.pow(map.get($SA98G, blkThrs) - $knownY, map.get($SA98G, blkClmp));
+    }
+
+    @if $knownType == 'bg' {
+        $knownExp:   map.get($SA98G, if($contrast > 0, normBG, revBG));
+        $unknownExp: map.get($SA98G, if($contrast > 0, normTXT, revTXT));
+        $unknownY:   math.pow(math.pow($knownY, $knownExp) - $contrast, math.div(1, $unknownExp));
+    } @else {
+        $knownExp:   map.get($SA98G, if($contrast > 0, normTXT, revTXT));
+        $unknownExp: map.get($SA98G, if($contrast > 0, normBG, revBG));
+        $unknownY:   math.pow($contrast + math.pow($knownY, $knownExp), math.div(1, $unknownExp));
+    }
+
+    @if '#{$unknownY}' == '#{math.sqrt(-1)}' {
+        @return false;
+    }
+
+    @if $unknownY > 1.06 or $unknownY < 0 {
+        @return false;
+    }
+
+    @if $unknownY <= map.get($SA98G, blkThrs) {
+        $unknownY: math.pow(
+            ($unknownY + map.get($SA98G, mOffsetIn)) * map.get($SA98G, mFactor),
+            math.div(map.get($SA98G, mExpAdj), map.get($SA98G, blkClmp))
+        ) * math.div(1, map.get($SA98G, mFactor)) - map.get($SA98G, mOffsetOut);
+    }
+
+    $unknownY: math.max(math.min($unknownY, 1), 0);
+
+    @return $unknownY;
+}