2-dimensional gradient using PGF

Question

I'd like to draw a square with the fill color darkening as one goes up or as one goes to the right. So, the square should be darkest in the upper-right corner and lightest in the lower-left corner. Is there a way to do this using PGF commands?

Answer 1

Such shadings are described in section 85.2 of the TikZ manual. Here's an example of what you want:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\pgfdeclareverticalshading{myshadingE}{80bp} 
{color(0bp)=(white); color(80bp)=(black)} 

\begin{pgfpicture} 
\pgfpathrectangle{\pgfpointorigin}{\pgfpoint{3cm}{3cm}} 
\pgfshadepath{myshadingE}{-45} 
\pgfusepath{stroke}
\end{pgfpicture} 
\end{document}

Answer 2

Another possibility is using tikz commands:

\documentclass{minimal}
\usepackage{tikz}
\begin{document}
\tikz\shade[shading=axis,bottom color=black!10,top color=black,shading angle=-45] 
  (0,0) rectangle (3,3);
\end{document}