如何制作可变颜色的PDF？

[ADSWT518]

我正在尝试修改SJTUBeamer的代码，将 https://github.com/sjtug/SJTUBeamer/tree/main/vi 文件夹下的 sjtu-vi-*.pdf 文件替换为我所需要的徽标。但是我发现 sjtu-vi-*.pdf 文件都是空白的，这样就可以直接在latex中将其改变为所需的颜色。

现在我有一个纯色的PDF文件，有什么办法可以将其转变为 sjtu-vi-*.pdf 文件类似的空白PDF吗？我不知道这种技术/文件的名称，模糊地搜索了一下也没有结果。

[ADSWT518]

我好像知道了，刚刚拿inkscape打开了 sjtu-vi-*.pdf 文件，发现实际上是把徽标变成了白色？然后我自己试着处理了一下，确实正常了。

[LogCreative]

这一块是在 SJTUBeamer 开发手册中讲述的：

SJTUBeamer/src/doc/sjtubeamerdevguide.tex

Lines 1005 to 1045 in 5ee4dc9

	\subsection{Logo System}
	\themename\ has its own color model on the logo. The main macro is
	\verb"\definelogo". You need to specify the control sequence name and the file
	path in the first two arguments.
	TikZ provides an environment to create our own path fading from picture:
	\verb"tikzfadingfrompicture", where you could define your fading in a $(-1,-1)$
	to $(1,1)$ rectangle area. Fill the background to black and insert a white logo
	in the middle will create a mask. Set the path fading to the name of this mask
	will apply to your new TikZ shape.
	However, this only creates a square mask. We have to crop it for some
	rectangular bounding boxes. Our macro will decide from your input on horizontal
	and vertical cropping size for your picture fill the height or fill the width.
	And crop the area symmetrically.
	\begin{figure}[h]
	\begin{tikzpicture}
	\draw [fill=black] (-4,1) rectangle (-2,-1);
	\node [white] at (-3,0) {\LARGE Logo};
	\node at (-3,-1.5) {\ttfamily tikzfadingfrompicture};
	\node at (-0.5,0) {$\rightarrow$};
	\draw (0.5,0.5) rectangle (3,-0.5);
	\node [red] at (1.75,0) {\LARGE Logo};
	\node at (1.75,-1.5) {\verb"\definelogo"};
	\node at (4,0) {$\rightarrow$};
	\node [blue] at (6,0) {\LARGE Logo};
	\node at (6,-1.5) {\verb"\logo[cprimary]"};
	\end{tikzpicture}
	\end{figure}
	The logo color is now controlled by the current text color. See Section
	\ref{sec:logoins} for how to modify the logo color for \verb"\insertlogo".
	Otherwise, the generated command can also receive an optional command for
	overriding color or changing the opacity or using any supported Ti\emph{k}Z
	argument for \verb"\fill". Sometimes, you need to specify the color for your
	logo object.

确实，如果像做可变颜色的徽标，就需要一个白色的徽标（任何图片格式：PDF、png等等），然后

SJTUBeamer/src/source/sjtuvi.dtx

Line 310 in 5ee4dc9

\definelogo{sjtubadge}{vi/sjtu-vi-sjtubadge.pdf}{0}{0}

就可以把logo定义出来。

如果需要普通的徽标，参见：#172

[ADSWT518]

了解了，我提问之前也看过开发手册，但当时没意识到只有白色才会再叠加了任何颜色之后变成指定的颜色 😂

谢谢您！

[LogCreative]

看来这种加密手段很有效果😂