6  Shadings (gradients)

cvd transforms TikZ/pgf shadings—both axial (linear) and radial gradients emitted by \shade, \shadedraw, and friends. The transformation is applied to the RGB or CMYK color stops at the moment pgf emits the shading’s PDF object. For CMYK, the K component is left unchanged.

6.1 Basic usage

Set the cvd type once before \begin{document} and any shading you draw will come out simulated:

\documentclass{article}
\usepackage{tikz}
\usepackage{cvd}

\cvdtype{deuteranopia}
\cvdseverity{1.0}
\cvdenable

\begin{document}
\begin{tikzpicture}
  \shade[left color=red, right color=blue] (0,0) rectangle (4,1);
\end{tikzpicture}
\end{document}

6.2 Comparing several cvd types in one document

Toggling \cvdtype between two \shade calls that use the same input colors does not produce two different gradients. pgf caches each shading by its input color stops (see \pgfuseshading in pgfcoreshade.code.tex); the second call hits the cache and reuses the PDF object emitted by the first, so the cvd state at the time of the second call has no effect.

The workaround is to pre-compute simulated colors with \cvddefinecolor and shade with those, leaving cvd disabled at draw time:

\cvddefinecolor[type=deuteranopia]{red}{red-d}
\cvddefinecolor[type=deuteranopia]{blue}{blue-d}
\cvddefinecolor[type=protanopia]{red}{red-p}
\cvddefinecolor[type=protanopia]{blue}{blue-p}

\begin{tikzpicture}
  \shade[left color=red,   right color=blue]   (0,0) rectangle (4,0.8);
  \shade[left color=red-d, right color=blue-d] (5,0) rectangle (9,0.8);
  \shade[left color=red-p, right color=blue-p] (0,-1.5) rectangle (4,-0.7);
\end{tikzpicture}

Each row uses different color names, so pgf’s cache key differs and each shading gets its own PDF object.

6.3 Known limitations

• Functional shadings (\pgfdeclarefunctionalshading, ShadingType 1) embed their colors inside a PostScript Type 4 function. cvd does not parse or rewrite that function, so functional shadings pass through unchanged.

• Cached duplicate shadings – as described above, two \shade calls with identical input colors share one PDF object. Use \cvddefinecolor to side-step the cache.