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## PSTricks | Cut off part of parallelogram if ...

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### PSTricks | Cut off part of parallelogram if ...

First: The topic probably needs a better headline. This was the best I could come up with.

Hi all.

Consider the following MWE, illustrating rays of light coming from the Sun through the Oculus in the Pantheon, Rome:

Code: Select all  •  Open in writeLaTeX
\documentclass{article}

\usepackage[locale=DE]{siunitx}
\usepackage{expl3}

\ExplSyntaxOn
\cs_new_eq:NN
\calculate
\fp_eval:n
\ExplSyntaxOff

\begin{document}

} % Radius of the dome
\def\vinkelA{12 }   % Width of the Oculus
\def\vinkelB{71 }   % Angle of the Sun's rays
\def\faktor{\calculate{1/3} }
\def\vinkelC{\calculate{90-\vinkelA} }
\def\vinkelD{\calculate{90+\vinkelA} }
\def\vinkelE{\calculate{180+\vinkelC} }
\def\vinkelF{\calculate{180+\vinkelD} }
\def\vinkelG{\calculate{180-\vinkelB} }
\def\vinkelH{\calculate{180+\vinkelG} }
\begin{figure}
\centering
\begin{pspicture}(44,50)
\psset{unit=0.5cm,linecolor=red}
\pnode(0,0){A}
\psset{linestyle=none,linecolor=black,dotsep=2pt}
\psRelLine[angle=\vinkelF](E)(B){1}{P1}
\psRelLine[angle=\vinkelE](E)(B){1}{P2}
\psRelLine[angle=\vinkelG](P1)(P2){1}{L1}
\psRelLine[angle=\vinkelH,linestyle=dotted](P2)(P1){1}{L2}
\psRelLine[angle=\vinkelG](P2)(P1){1 \vinkelA cos add 2 \vinkelA sin mul \vinkelB sin mul div}{L3}
\psParallelLine(L2)(L3)(L1){1}{L4}
\pspolygon[fillstyle=solid,fillcolor=yellow](L1)(L2)(L3)(L4)
\pcline[linestyle=dotted](T1)(T2)
\psline[linestyle=solid,linecolor=red](C)(D)(A)(B)
\end{pspicture}
\end{figure}

\end{document
}

I would like to cut off the yellow parallelogram if it reaches the right, vertical part of the red curve, i.e., if the rays of light hit the wall. How do I do this?

P.S. If you spot a way to make the code (more) elegant and/or efficient, I will be glad to know.

Update:
Come to think of it, I would also like the parallelogram to be cut off if it reaches the left, vertical part of the red curve.

Update 2:
Attachments
Angles for the rays to hit the floor only.
angles.png (29.58 KiB) Viewed 884 times
In the game of chess, you can never let your adversary see your pieces.''
-- Zapp Brannigan, Futurama (season 1, episode 4)

svend_tveskaeg

Posts: 475
Joined: Sun Jul 12th, 2009
Location: Aarhus, Denmark

### Re: PSTricks | Cut off Part of Parallelogram if ...

I have cross-posted this question to {TeX} SX.
In the game of chess, you can never let your adversary see your pieces.''
-- Zapp Brannigan, Futurama (season 1, episode 4)

svend_tveskaeg

Posts: 475
Joined: Sun Jul 12th, 2009
Location: Aarhus, Denmark

### Re: PSTricks | Cut off part of parallelogram if ...

The user percusse has come up with a solution on {TeX} SX.
In the game of chess, you can never let your adversary see your pieces.''
-- Zapp Brannigan, Futurama (season 1, episode 4)

svend_tveskaeg

Posts: 475
Joined: Sun Jul 12th, 2009
Location: Aarhus, Denmark

### Re: PSTricks | Cut off part of parallelogram if ...

svend_tveskaeg wrote:Consider the following MWE, illustrating rays of light coming from the Sun through the Oculus in the Pantheon, Rome:

it is easier to use a simple line for the sun ray

Code: Select all  •  Open in writeLaTeX
\documentclass[pstricks]{standalone}
\usepackage[locale=DE]{siunitx}

\begin{document}
} % Radius of the dome
\def\faktor{0.3333}
\def\vinkelA{12
}   % Width of the Oculus
\makeatletter
\pst@getsinandcos{\vinkelA}
\pstFPmul\MaxLW{2}{\MaxLW}

\multido{\iA=10+5}{16
}{% % Angle of the Sun's rays
\psset{unit=0.5cm}
\pst@getsinandcos{\iA}
\pstFPmul\RelLW{\MaxLW}{\pst@sin}
\pnode(0,0){C}
}
\pcline[linecolor=yellow,linewidth=\RelLW,nodesepB=-8,nodesepA=-1]%
(0,0)(!-1 \iA\space neg Tan neg)}
\begin{psclip}{%
\pscustom[linewidth=2pt,linecolor=red,fillstyle=solid,fillcolor=blue!20]{%
\psline(B)(A)(D)
}
\pcline[linecolor=yellow,linewidth=\RelLW,nodesep=-4]%
(0,0)(!\RelRadius\space dup \iA\space neg Tan mul )}
\end{psclip}
}|T1)
\pswedge(0,0){1}{!180 \iA\space sub}{180}
\uput{1}[!180 \iA\space 2 div sub](0,0){\footnotesize\SI{\iA}{\degree}}
\psline[linestyle=dotted](0,0)(!3 180 \iA\space sub PtoC)
}
\end{pspicture}}

\end{document
}
Attachments
demo.gif (74.51 KiB) Viewed 826 times
CrazyHorse

Posts: 350
Joined: Sat Aug 2nd, 2008

### Re: PSTricks | Cut off part of parallelogram if ...

@Herbert: Awesome!
In the game of chess, you can never let your adversary see your pieces.''
-- Zapp Brannigan, Futurama (season 1, episode 4)

svend_tveskaeg

Posts: 475
Joined: Sun Jul 12th, 2009
Location: Aarhus, Denmark