513 lines
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513 lines
16 KiB
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</head>
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<body>
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<h1 class="title toc-ignore">ANSI CSI SGR Sequences in Rmarkdown</h1>
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<h4 class="author">Brodie Gaslam</h4>
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<div id="browsers-do-not-interpret-ansi-csi-sgr-sequences" class="section level3">
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<h3>Browsers Do Not Interpret ANSI CSI SGR Sequences</h3>
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<p>Over the past few years color has been gaining traction in the R
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terminal, particularly since Gábor Csárdi’s <a href="https://github.com/r-lib/crayon">crayon</a> made it easy to format
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text with <a href="https://en.wikipedia.org/wiki/ANSI_escape_code">ANSI
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CSI SGR sequences</a>. At the same time the advent of JJ Alaire and
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Yihui Xie <code>rmarkdown</code> and <code>knitr</code> packages, along
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with John MacFarlane <code>pandoc</code>, made it easy to automatically
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incorporate R code and output in HTML documents.</p>
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<p>Unfortunately ANSI CSI SGR sequences are not recognized by web
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browsers and end up rendering weirdly<a href="#f1"><sup>1</sub></a>:</p>
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<div class="sourceCode" id="cb1"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb1-1"><a href="#cb1-1" tabindex="-1"></a>sgr.string <span class="ot"><-</span> <span class="fu">c</span>(</span>
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<span id="cb1-2"><a href="#cb1-2" tabindex="-1"></a> <span class="st">"</span><span class="sc">\033</span><span class="st">[43;34mday > night</span><span class="sc">\033</span><span class="st">[0m"</span>,</span>
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<span id="cb1-3"><a href="#cb1-3" tabindex="-1"></a> <span class="st">"</span><span class="sc">\033</span><span class="st">[44;33mdawn < dusk</span><span class="sc">\033</span><span class="st">[0m"</span></span>
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<span id="cb1-4"><a href="#cb1-4" tabindex="-1"></a>)</span>
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<span id="cb1-5"><a href="#cb1-5" tabindex="-1"></a><span class="fu">writeLines</span>(sgr.string)</span></code></pre></div>
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<pre><code>## <20>[43;34mday > night<68>[0m
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## <20>[44;33mdawn < dusk<73>[0m</code></pre>
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</div>
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<div id="automatically-convert-ansi-csi-sgr-to-html" class="section level3">
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<h3>Automatically Convert ANSI CSI SGR to HTML</h3>
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<p><code>fansi</code> provides the <code>to_html</code> function which
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converts the ANSI CSI SGR sequences and OSC hyperlinks into HTML markup.
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When we combine it with <code>knitr::knit_hooks</code> we can modify the
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rendering of the <code>rmarkdown</code> document such that ANSI CSI SGR
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encoding is shown in the equivalent HTML.</p>
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<p><code>fansi::set_knit_hooks</code> is a convenience function that
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does just this. You should call it in an <code>rmarkdown</code> document
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with the:</p>
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<ul>
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<li>Chunk option <code>results</code> set to “asis”.</li>
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<li>Chunk option <code>comments</code> set to “” (empty string).</li>
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<li>The <code>knitr::knit_hooks</code> object as an argument.</li>
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</ul>
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<p>The corresponding <code>rmarkdown</code> hunk should look as
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follows:</p>
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<pre><code>```{r, comment="", results="asis"}
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old.hooks <- fansi::set_knit_hooks(knitr::knit_hooks)
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```</code></pre>
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<STYLE type="text/css" scoped>
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PRE.fansi SPAN {padding-top: .25em; padding-bottom: .25em};
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</STYLE>
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<p>We run this function for its side effects, which cause the output to
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be displayed as intended:</p>
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<div class="sourceCode" id="cb4"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb4-1"><a href="#cb4-1" tabindex="-1"></a><span class="fu">writeLines</span>(sgr.string)</span></code></pre></div>
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<PRE class="fansi fansi-output"><CODE>## <span style="color: #0000BB; background-color: #BBBB00;">day > night</span>
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## <span style="color: #BBBB00; background-color: #0000BB;">dawn < dusk</span>
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</CODE></PRE>
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<p>If you are seeing extra line breaks in your output you may need to
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use:</p>
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<pre><code>```{r, comment="", results="asis"}
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old.hooks <- fansi::set_knit_hooks(knitr::knit_hooks, split.nl=TRUE)
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```</code></pre>
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<p>If you use <code>crayon</code> to generate your ANSI CSI SGR style
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strings you may need to set <code>options(crayon.enabled=TRUE)</code>,
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as in some cases <code>crayon</code> suppresses the SGR markup if it
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thinks it is not outputting to a terminal.</p>
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<p>We can also set hooks for the other types of outputs, and add some
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additional CSS styles.</p>
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<pre><code>```{r, comment="", results="asis"}
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styles <- c(
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getOption("fansi.style", dflt_css()), # default style
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"PRE.fansi CODE {background-color: transparent;}",
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"PRE.fansi-error {background-color: #DDAAAA;}",
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"PRE.fansi-warning {background-color: #DDDDAA;}",
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"PRE.fansi-message {background-color: #AAAADD;}"
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)
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old.hooks <- c(
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old.hooks,
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fansi::set_knit_hooks(
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knitr::knit_hooks,
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which=c("warning", "error", "message"),
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style=styles
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) )
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```</code></pre>
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<STYLE type="text/css" scoped>
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PRE.fansi SPAN {padding-top: .25em; padding-bottom: .25em};
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PRE.fansi CODE {background-color: transparent;}
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PRE.fansi-message {background-color: #AAAADD;}
|
||
</STYLE>
|
||
<div class="sourceCode" id="cb7"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb7-1"><a href="#cb7-1" tabindex="-1"></a><span class="fu">message</span>(<span class="fu">paste0</span>(sgr.string, <span class="at">collapse=</span><span class="st">"</span><span class="sc">\n</span><span class="st">"</span>))</span></code></pre></div>
|
||
<PRE class="fansi fansi-message"><CODE>## <span style="color: #0000BB; background-color: #BBBB00;">day > night</span>
|
||
## <span style="color: #BBBB00; background-color: #0000BB;">dawn < dusk</span>
|
||
</CODE></PRE>
|
||
<div class="sourceCode" id="cb8"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb8-1"><a href="#cb8-1" tabindex="-1"></a><span class="fu">warning</span>(<span class="fu">paste0</span>(<span class="fu">c</span>(<span class="st">""</span>, sgr.string), <span class="at">collapse=</span><span class="st">"</span><span class="sc">\n</span><span class="st">"</span>))</span></code></pre></div>
|
||
<PRE class="fansi fansi-warning"><CODE>## Warning:
|
||
## <span style="color: #0000BB; background-color: #BBBB00;">day > night</span>
|
||
## <span style="color: #BBBB00; background-color: #0000BB;">dawn < dusk</span>
|
||
</CODE></PRE>
|
||
<div class="sourceCode" id="cb9"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb9-1"><a href="#cb9-1" tabindex="-1"></a><span class="fu">stop</span>(<span class="fu">paste0</span>(<span class="fu">c</span>(<span class="st">""</span>, sgr.string), <span class="at">collapse=</span><span class="st">"</span><span class="sc">\n</span><span class="st">"</span>))</span></code></pre></div>
|
||
<PRE class="fansi fansi-error"><CODE>## Error in eval(expr, envir, enclos):
|
||
## <span style="color: #0000BB; background-color: #BBBB00;">day > night</span>
|
||
## <span style="color: #BBBB00; background-color: #0000BB;">dawn < dusk</span>
|
||
</CODE></PRE>
|
||
<p>You can restore the old hooks at any time in your document with:</p>
|
||
<div class="sourceCode" id="cb10"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb10-1"><a href="#cb10-1" tabindex="-1"></a><span class="fu">do.call</span>(knitr<span class="sc">::</span>knit_hooks<span class="sc">$</span>set, old.hooks)</span>
|
||
<span id="cb10-2"><a href="#cb10-2" tabindex="-1"></a><span class="fu">writeLines</span>(sgr.string)</span></code></pre></div>
|
||
<pre><code>## <20>[43;34mday > night<68>[0m
|
||
## <20>[44;33mdawn < dusk<73>[0m</code></pre>
|
||
<p>See <code>?fansi::set_knit_hooks</code> for details.</p>
|
||
<hr />
|
||
<p><a name="f1"></a><sup>1</sup>For illustrative purposes we output raw
|
||
ANSI CSI SGR sequences in this document. However, because the ESC
|
||
control character causes problems with some HTML rendering services we
|
||
replace it with the <20> symbol. Depending on the browser and process it
|
||
would normally not be visible at all, or substituted with some other
|
||
symbol.</p>
|
||
</div>
|
||
|
||
|
||
|
||
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