[css-color] DCI P3 support in conversion code

Author: svgeesus

css-color/Overview.bs

@@ -1769,18 +1769,15 @@ Implementations may choose to implement these steps in some other way (for examp
 using an ICC profile with relative colorimetric rendering intent) provided the results 
 are the same for colors inside the source and destination gamuts.
 
-<h3 id="at-profile">Specifying a color profile: the ''profile'' at-rule</h3>
-<!-- we agreed to call it profile rather than color-profile or icc-profile, for brevity -->
+<h3 id="at-profile">Specifying a color profile: the ''color-profile'' at-rule</h3>
 
 The <dfn data-dfn-type='at-rule' id="at-ruledef-profile">@color-profile</dfn> 
 rule is a  group rule.  It consists of the at-keyword
-'@color-profile' followed by an identifier, followed by a group rule body.
+'@color-profile' followed by a name, followed by a group rule body.
 
 In a very similar way to the ''<@font-face.'' at-rule, the ''<@color-profile>'' 
-at-rule has a descriptor 
-to give the profile a name which will be used inside the stylesheet, 
-<!-- is this actualy a descriptor, or a parameter to the at-rule?-->
-and another descriptor to point to the actual 
+at-rule has a name (which will be used inside the stylesheet), 
+and a descriptor to point to the actual 
 data (<dfn for="@color-profile/src">src</dfn>, just like 
 <dfn for="@font-face/src">src</dfn> in font-face.) 
 <!-- not clear how I link to the two different descriptors therte, in bikeshed syntax -->

css-color/conversions.js

@@ -50,6 +50,53 @@ function XYZ_to_lin_sRGB(XYZ) {
 	return math.multiply(M, XYZ).valueOf();
 }
 
+// DCI P3-related functions
+
+
+function lin_P3(RGB) {
+	// convert an array of DCI P3 RGB values in the range 0.0 - 1.0 
+	// to linear light (un-companded) form.
+
+	return RGB.map(function (val) {
+		return Math.pow(val, 2.6);
+	});
+}
+
+function gam_P3(RGB) {
+	// convert an array of linear-light P3 RGB  in the range 0.0-1.0
+	// to gamma corrected form
+	
+	return RGB.map(function (val) {
+			return Math.pow(val, 1/2.6);
+		}
+	});
+}
+ 
+function lin_P3_to_XYZ(rgb) {
+	// convert an array of linear-light P3 values to CIE XYZ
+	// using  D65 (no chromatic adaptation)
+	// http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html
+	var M = math.matrix([
+		[0.4865709486482162, 0.26566769316909306, 0.1982172852343625],
+		[0.2289745640697488, 0.6917385218365064,  0.079286914093745], 
+		[0.0000000000000000, 0.04511338185890264, 1.043944368900976]
+	]);
+	// 0 was computed as -3.972075516933488e-17
+	
+	return math.multiply(M, rgb).valueOf();
+}
+
+function XYZ_to_lin_P3(XYZ) {
+	// convert XYZ to linear-light P3
+	var M = math.matrix([
+		[ 2.493496911941425,   -0.9313836179191239, -0.40271078445071684],
+		[-0.8294889695615747,   1.7626640603183463,  0.023624685841943577],
+		[ 0.03584583024378447, -0.07617238926804182, 0.9568845240076872]
+	]);
+	
+	return math.multiply(M, XYZ).valueOf();
+}
+
 //Rec.2020-related functions
 
 function lin_2020(RGB) {

css-color/matrixmaker.html

@@ -13,7 +13,7 @@
 
 
 		// these are for ITU Rec BT.2020
-		
+		/*		
 		const xred=0.708 ;
 		const yred=0.292 ;
 		
@@ -22,7 +22,17 @@
 		
 		const xblue=0.131 ;
 		const yblue=0.046 ;
+		*/
+		
+		// these are for DCI P3
+		const xred=0.680 ;
+		const yred=0.320 ;
 
+		const xgreen=0.265 ;
+		const ygreen=0.690 ;
+		
+		const xblue=0.150 ;
+		const yblue=0.060 ;
 
 		// AdobeRGB, for testing
 		/*