弯曲管子的遮光

Question 1

这似乎是 TeX.SE 问答中尚未解决的一个问题。

打击乐产生了可用的解决方案
约翰内斯提出了类似的问题，但针对的是形状

还存在一些回避问题或与改进答案相关的问题。

这例如处理阴影

扩展 Percusse 的代码并将其包装成一组 TikZ/PGF 键，使其对其他人有用。我创建了两个键diffuse gradient和，diffuse falloff它们通过多次回溯路径来绘制阴影线。

\documentclass[tikz]{standalone}
\usepackage{graphicx}

\usetikzlibrary{positioning}

\tikzset{
 diffuse color/.initial = black,                       % (1) The color value does not carry through to the pre- and post- actions
}

\tikzset{
 linear opacity/.initial=0.5,                          %     Initial value must be defined here to define the next key
 linear stroke/.style = {                              %     Define a style to draw a diffused sstroke
   preaction={                                         %     This uses preactions to draw the gradiens
     draw=\pgfkeysvalueof{/tikz/diffuse color},        %     Draw and colour the path (See 1). This is disabled by `/tikz/diffuse gradient' (See 2)
     line width = (2.0-#1)*\pgflinewidth,              %     Vary the Line width for each stroke, change 2.0 to 1.0 to normalize scaling
     opacity=\pgfkeysvalueof{/tikz/linear opacity}}},  %     Keep resetting the opacity for each line, there is probably a cleaner means of setting this (See 3)
 diffuse gradient/.style={                             %     This style executes `/tikz/diffuse' stroke multiple times to achieve the gradient effect
   draw = none,                                        % (2) Disable the default draw operation
   linear opacity=#1,                                  % (3) Set a consistent value for opacity. In retrospect one could have simply assigned this to /tikz/opacity
   linear stroke/.list={0.0,#1,...,1.0}},              %     Draw the line multiple times. Ideally we would use (1.0-1/#1) as the final value and (1/#1) as the stepsize
 diffuse gradient/.default=1,                          %     Set an initial step size
}

\tikzset{
 non-linear stroke/.style = {                          %     Define a style to draw a diffused sstroke
   preaction={                                         %     This uses preactions to draw the gradiens
     draw=\pgfkeysvalueof{/tikz/diffuse color},        %     Draw and colour the path (See 1). This is disabled by `/tikz/diffuse falloff' (See 4)
     line width = (2.0-#1)*\pgflinewidth,              %     Vary the Line width for each stroke, change 2.0 to 1.0 to normalize scaling
     opacity=#1}},                                     %     Vary the opacity for each stroke
 diffuse falloff/.style={                              %     This style executes `/tikz/diffuse' stroke multiple times to achieve the gradient effect
   draw = none,                                        % (4) Disable the default draw operation
   non-linear stroke/.list={0.0,#1,...,1.0}},          %     Draw the line multiple times. Ideally we would use (1.0-1/#1) as the final value and (1/#1) as the stepsize
 diffuse falloff/.default=1,                           %     Set an initial step size
}

\begin{document}

\begin{tikzpicture}
\draw [line width = 5pt, diffuse gradient= 0.5]                        (0, 3em) ++ (-1, -1) -- coordinate (A) ++ (1,1);
\draw [line width = 5pt, diffuse gradient=0.05]                        (0, 0em) ++ (-1, -1) -- coordinate (B) ++ (1,1);
\draw [line width = 5pt, diffuse gradient=0.25,postaction={draw, red}] (0,-3em) ++ (-1, -1) -- coordinate (C) ++ (1,1);
\node[right=of A] {Coarse Gradient};
\node[right=of B] {Fine Gradient};
\node[right=of C] {Enforced Line};
\end{tikzpicture}
\begin{tikzpicture}
\draw [line width = 5pt, diffuse falloff= 0.3]                        (0, 3em) ++ (-1, -1) -- coordinate (A) ++ (1,1);
\draw [line width = 5pt, diffuse falloff=0.05]                        (0, 0em) ++ (-1, -1) -- coordinate (B) ++ (1,1);
\draw [line width = 5pt, diffuse falloff=0.25,postaction={draw, red}] (0,-3em) ++ (-1, -1) -- coordinate (C) ++ (1,1);
\node[right=of A] {Coarse Gradient};
\node[right=of B] {Fine Gradient};
\node[right=of C] {Enforced Line};
\end{tikzpicture}

\end{document}

代码注释得很好，因此人们可以了解发生了什么（这更多是供我自己参考，而不是其他任何东西）。颜色分配是一种解决方法。请注意，使用着色器时颜色会略微褪色diffuse gradient，我不太确定这是为什么。示例输出中的粗渐变线和细渐变线沿中心都应该是黑色，后者是灰色。

由于diffuse falloff线条更加清晰，因此可能会产生更好的“管子”。原始颜色也得以保留。

强制线条实际上只是为了展示，并突出了着色策略的差异。红色表示通常的线条可能被绘制的位置，这实际上有点被理解为乘法常数 2.0 将实际线宽加倍。如果使用代码，则应将其设置为 1.0，或者将其转换为参数line spread。

阴影的绘制方式允许自然的交叉，如下所示

当然还有动画。

涟漪是用以下方法制成的：

\foreach \n in {0,0.025,...,1} {
 \begin{tikzpicture}
 \fill [inner color=blue!40!black, outer color=blue!60!black] circle (4em);
 \begin{scope}
 \path [clip] circle (4em);
  \pgfmathsetmacro{\rA}{0.0 + mod(\n,1)} 
  \pgfmathsetmacro{\xA}{ 75 - 5*mod(\n,1)}
  \draw [diffuse color = blue!\xA!black, line width = 2pt, diffuse falloff = 0.25] (0,0) circle (\rA em);
  \pgfmathsetmacro{\rB}{1.0 + mod(\n,1)}
  \pgfmathsetmacro{\xB}{ 70 - 5*mod(\n,1)}
  \draw [diffuse color = blue!\xB!black, line width = 2pt, diffuse falloff = 0.25] (0,0) circle (\rB em);
  \pgfmathsetmacro{\rC}{2.0 + mod(\n,1)}
  \pgfmathsetmacro{\xC}{ 65 - 5*mod(\n,1)}
  \draw [diffuse color = blue!\xC!black, line width = 2pt, diffuse falloff = 0.25] (0,0) circle (\rC em);
  \pgfmathsetmacro{\rD}{3.0 + mod(\n,1)}
  \pgfmathsetmacro{\xD}{ 60 - 5*mod(\n,1)}
  \draw [diffuse color = blue!\xD!black, line width = 2pt, diffuse gradient= 0.25] (0,0) circle (\rD em);
 \end{scope}
 \end{tikzpicture}
}

更新：

使用以下代码绘制管道。

\begin{tikzpicture}[
 detail/.style = {
  preaction={draw, every diffuse, line width=2.1*\pgflinewidth, black}, 
  preaction={draw, every diffuse, line width=2*\pgflinewidth, red}, 
  diffuse color=red!50!blue, 
  diffuse gradient=0.06,
  rounded corners=0.75em,
 },
 square tube/.style={
  line width = 0.25em,
  every diffuse/.append style={line cap=rect},
  detail
 },
 round tube/.style={
  line width = 0.25em,
  every diffuse/.append style={line cap=round},
  detail
 }
]
\draw[square tube] ( 0em, -1em) -| ( 2em, 1em) ( 3em,-1.5em) -- ( 3em,1em);
\draw[round tube]  ( 0em, -1em) -| (-2em, 1em) (-3em,-1.5em) -- (-3em,1em);
% \draw [thick, diffuse falloff= 0.3] (120:-120:1em);
\end{tikzpicture}

@cfr 每个人都是批评家 ;P

Answer