contrast() now accepts percentage threshold

Fixes #501.
Closes #523.

Author: atkaye

lessc.inc.php

@@ -1283,36 +1283,43 @@ protected function lib_mix($args) {
 	}
 
 	protected function lib_contrast($args) {
-	    $darkColor  = array('color', 0, 0, 0);
-	    $lightColor = array('color', 255, 255, 255);
-	    $threshold  = 0.43;
-
-	    if ( $args[0] == 'list' ) {
-	        $inputColor = ( isset($args[2][0]) ) ? $this->assertColor($args[2][0])  : $lightColor;
-	        $darkColor  = ( isset($args[2][1]) ) ? $this->assertColor($args[2][1])  : $darkColor;
-	        $lightColor = ( isset($args[2][2]) ) ? $this->assertColor($args[2][2])  : $lightColor;
-	        $threshold  = ( isset($args[2][3]) ) ? $this->assertNumber($args[2][3]) : $threshold;
-	    }
-	    else {
-	        $inputColor  = $this->assertColor($args);
-	    }
-
-	    $inputColor = $this->coerceColor($inputColor);
-	    $darkColor  = $this->coerceColor($darkColor);
-	    $lightColor = $this->coerceColor($lightColor);
-
-	    //Figure out which is actually light and dark!
-	    if ( $this->toLuma($darkColor) > $this->toLuma($lightColor) ) {
-	        $t  = $lightColor;
-	        $lightColor = $darkColor;
-	        $darkColor  = $t;
-	    }
-
-	    $inputColor_alpha = $this->lib_alpha($inputColor);
-	    if ( ( $this->toLuma($inputColor) * $inputColor_alpha) < $threshold) {
-	        return $lightColor;
-	    }
-	    return $darkColor;
+		$darkColor  = array('color', 0, 0, 0);
+		$lightColor = array('color', 255, 255, 255);
+		$threshold  = 0.43;
+
+		if ( $args[0] == 'list' ) {
+			$inputColor = ( isset($args[2][0]) ) ? $this->assertColor($args[2][0])  : $lightColor;
+			$darkColor  = ( isset($args[2][1]) ) ? $this->assertColor($args[2][1])  : $darkColor;
+			$lightColor = ( isset($args[2][2]) ) ? $this->assertColor($args[2][2])  : $lightColor;
+
+			if ( isset($args[2][3]) ) {
+				if ( isset($args[2][3][2]) && $args[2][3][2] === '%' ) {
+					$args[2][3][1] /= 100;
+					unset($args[2][3][2]);
+				}
+				$threshold = $this->assertNumber($args[2][3]);
+			}
+		}
+		else {
+			$inputColor  = $this->assertColor($args);
+		}
+
+		$inputColor = $this->coerceColor($inputColor);
+		$darkColor  = $this->coerceColor($darkColor);
+		$lightColor = $this->coerceColor($lightColor);
+
+		//Figure out which is actually light and dark!
+		if ( $this->toLuma($darkColor) > $this->toLuma($lightColor) ) {
+			$t  = $lightColor;
+			$lightColor = $darkColor;
+			$darkColor  = $t;
+		}
+
+		$inputColor_alpha = $this->lib_alpha($inputColor);
+		if ( ( $this->toLuma($inputColor) * $inputColor_alpha) < $threshold) {
+			return $lightColor;
+		}
+		return $darkColor;
 	}
 
 	private function toLuma($color) {

tests/inputs/colors.less

@@ -98,6 +98,9 @@ fade {
 .contrast {
 	color1: contrast(#000, red, blue);
 	color2: contrast(#fff, red, blue);
+	color3: contrast(#333, #000, #fff); // Default threshold
+	color4: contrast(#333, #000, #fff, 0.1); // Threshold weighted towards dark colour
+	color5: contrast(#333, #000, #fff, 10%); // Threshold weighted as percentage
 }
 
 .luma {

tests/outputs/colors.css

@@ -68,6 +68,9 @@ fade {
 .contrast {
   color1: #ff0000;
   color2: #0000ff;
+  color3: #ffffff;
+  color4: #000000;
+  color5: #000000;
 }
 .luma {
   color: 44.11161568%;