Support RGB and gray color models in ConTeXt

The `RGB` support was copied from the the Plain TeX definitions, `tex/generic/pgf/utilities/pgfutil-plain.def:29-37`, which is from #772. The `gray` color model now maps to the grayscale and not to `rgb`. Signed-off-by: Max Chernoff <[email protected]>
pgf-tikz · Feb 6, 2022 · e48ff0f · e48ff0f
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diff --git a/doc/generic/pgf/CHANGELOG.md b/doc/generic/pgf/CHANGELOG.md
@@ -73,6 +73,7 @@ lot of contributed changes. Thanks to everyone who volunteered their time!
 - Form-only patterns have no specified color #1122 
 - Make `graphdrawing` work with `name prefix` and `name suffix` options #1087
 - pgfkeys was a bit too relaxed around `\relax` #1132
+- Add `RGB` and `gray` color model support for ConTeXt #1130
 
 ### Changed
 
@@ -95,6 +96,7 @@ lot of contributed changes. Thanks to everyone who volunteered their time!
 - Jonathan Spratte
 - Joseph Wright
 - Mario Frasca
+- Max Chernoff
 - Michael Kuron
 - Michal Hoftich
 - muzimuzhi

diff --git a/tex/generic/pgf/utilities/pgfutil-context.def b/tex/generic/pgf/utilities/pgfutil-context.def
@@ -26,8 +26,17 @@
 \def\pgfutil@definecolor#1#2#3{\csname pgfutil@emu@#2\endcsname{#1}#3\@nil}
 
 \def\pgfutil@emu@rgb#1#2,#3,#4\@nil{\expandafter\def\csname\string\color@#1\endcsname{\xcolor@{}{}{rgb}{#2,#3,#4}}}
-\def\pgfutil@emu@gray#1#2\@nil{\expandafter\def\csname\string\color@#1\endcsname{\xcolor@{}{}{rgb}{#2,#2,#2}}}
+\def\pgfutil@emu@gray#1#2\@nil{\expandafter\def\csname\string\color@#1\endcsname{\xcolor@{}{}{gray}{#2}}}
 \def\pgfutil@emu@cmyk#1#2,#3,#4,#5\@nil{\expandafter\def\csname\string\color@#1\endcsname{\xcolor@{}{}{cmyk}{#2,#3,#4,#5}}}
+\def\pgfutil@emu@RGB#1#2,#3,#4\@nil{%
+    \begingroup
+    \pgfmathdivide@{#2}{255}\let\pgfutil@emu@RGB@r\pgfmathresult
+    \pgfmathdivide@{#3}{255}\let\pgfutil@emu@RGB@g\pgfmathresult
+    \pgfmathdivide@{#4}{255}\let\pgfutil@emu@RGB@b\pgfmathresult
+    \edef\pgf@marshal{\def\expandafter\noexpand\csname\string\color@#1\endcsname{%
+        \noexpand\xcolor@{}{}{rgb}{\pgfutil@emu@RGB@r,\pgfutil@emu@RGB@g,\pgfutil@emu@RGB@b}}}%
+    \expandafter\endgroup\pgf@marshal
+}
 
 
 % no need for x colors (users can load it if needed)