TikZ: Rectangle with diagonal fill (two colors)

Question

I'm trying to fill half of my rectangle with a green color. I would like the transition to be along a diagonal of the rectangle.

Here is the code I have currently

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shadows}
\begin{document}
\begin{tikzpicture}
\node [rectangle,draw,thick,text width=1.5cm,minimum height=1.5cm,
        text centered,rounded corners, drop shadow, fill=yellow, name = re] {Test};
\end{tikzpicture}
\end{document}

This (of course) gives me an only yellow rectangle. I would like something like this instead.

I have looked at http://www.texample.net/tikz/examples/rectangle-node-with-diagonal-fill/, but I didn't get it to work with the drop shadow (and it seems like a lot of code for a simple task).

I'm considering drawing an invisible triangle under the rectangle with clipping, but I'm not sure how to do that, or if it's the smartest way.

Answer 1

A short answer with some trick. Rectangle is drawn twice:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shadows}
\begin{document}
\begin{tikzpicture}
\node [rectangle,draw,text width=1.5cm,minimum height=1.5cm,
        text centered,rounded corners,name = re] {};
       \filldraw[yellow!80,drop shadow][] (re.south west)
        [rounded corners=4pt] -- (re.south east)
        [rounded corners=4pt] -- (re.north east)--cycle
        ;
        \filldraw[green!80][] (re.south west)
        [rounded corners=4pt] -- (re.north west)
        [rounded corners=4pt] -- (re.north east)--cycle
        ;
\node [rectangle,draw,thick, text width=1.5cm,minimum height=1.5cm,
        text centered,rounded corners,name = re] {Text};      
\end{tikzpicture}
\end{document}

EDIT: This edit offers by OP. He/she edit my answer and found a new solution.

Now only drawing one rectangle, and diagonal is completely straight.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shadows}
\tikzset{
diagonal fill/.style 2 args={fill=#2, path picture={
\fill[#1, sharp corners] (path picture bounding box.south west) -|
                         (path picture bounding box.north east) -- cycle;}},
reversed diagonal fill/.style 2 args={fill=#2, path picture={
\fill[#1, sharp corners] (path picture bounding box.north west) |- 
                         (path picture bounding box.south east) -- cycle;}}
}
% (reversed) diagonal fill={lower color}{upper color}
\begin{document}
\begin{tikzpicture}
\node[diagonal fill={yellow}{green!80},
      text width=1.5cm, minimum height=1.5cm,
      text centered, rounded corners, draw, drop shadow]{Text};
\end{tikzpicture}
\end{document}

Answer 2

Stumbling upon How to shade text in different colors? I remembered this question and thought it could be done using shading, so stealing the idea from TikZ Fading Speed we can define a sharp shading and fill the node with it. That gives total control over the angle and the node shape.

\documentclass[tikz, margin=3mm]{standalone}
\usetikzlibrary{shadows,shadings,shapes.symbols}
\tikzset{
    double color fill/.code 2 args={
        \pgfdeclareverticalshading[%
            tikz@axis@top,tikz@axis@middle,tikz@axis@bottom%
        ]{diagonalfill}{100bp}{%
            color(0bp)=(tikz@axis@bottom);
            color(50bp)=(tikz@axis@bottom);
            color(50bp)=(tikz@axis@middle);
            color(50bp)=(tikz@axis@top);
            color(100bp)=(tikz@axis@top)
        }
        \tikzset{shade, left color=#1, right color=#2, shading=diagonalfill}
    }
}

\begin{document}
\begin{tikzpicture}[my node/.style={draw, cloud, cloud ignores aspect, drop shadow, double color fill={green}{blue}}]
\foreach \angle[count=\i] in {0,15,...,75} \node[my node, shading angle=\angle] (a\i) at (0,\i) {Text};
\foreach \angle[count=\i] in {105,120,...,180} \node[my node, shading angle=\angle] (b\i) at (3,\i) {Text};
\path (a6) -- node[my node, shading angle=90]{Text} (b1);
\end{tikzpicture}
\end{document}

Answer 3

Putting a node inside a multi-parameters pic is a way. The options [rounded corners], [save path], [use path], and [clip] are just good to be together.

\documentclass[tikz,border=5mm]{standalone}
\begin{document}
\begin{tikzpicture}
% #1 and #2 are colors; 
% #3 is node name (note: no space in node name)
% #4 is text of the node. It can be empty   
\tikzset{pics/colorfulbox/.style args=
{#1|#2|#3|#4}{code={%
\path (0,0) node[minimum size=1cm,rounded corners,save path=\temppath] (#3) {};
\begin{scope}
\clip[use path=\temppath];
\fill[#1] (#3.45)-|(#3.-135)--cycle;
\fill[#2] (#3.45)|-(#3.-135)--cycle;
\end{scope}
\path (0,0) node[draw,minimum size=1cm,rounded corners] (#3) {#4};
}}} 
        
\path
(0,0)  pic{colorfulbox= cyan | magenta |A|}
(3,2)  pic{colorfulbox=violet|yellow|B|}
(-1,3) pic{colorfulbox=brown|orange|C|C}
;
\draw (A)--(B);
\draw[->] (A) -| (B);
\draw[stealth-] (A) to[out=120,in=80] (B); 
\end{tikzpicture}
\end{document}