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<h2><a href="index.html">Back to Table of Contents</a></h2>
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<div id="content">
<h1 class="title">Peek definition with Emacs frame</h1>
<p>
In many IDEs, peek definition is a feature that opens a definition (of a
function, a class, a symbol, etc) in a popup window without leaving the current
buffer. Most of the time, jumping into a definition, then jump back, is
enough, so why bother leaving the current buffer to reload a whole new buffer,
then go back for another reload. This is distracting.
</p>
<p>
An example of peek definition:
</p>
<p>
<a href="static/peek-definition-vs.png"><img src="static/peek-definition-vs.png" alt="peek-definition-vs.png" /></a>
(Source: Microsoft)
</p>
<p>
I already searched for an alternative in Emacs, but apparently, all the
solutions that involve a popup is slow and lacking. The space for displaying
text is limited, and there is no font locking. You can't even search, or if it
does, search is difficult and slow.
</p>
<p>
Recently, while jumping around code definitions, I lost track of the original
buffer I start the jump chain, e.g. I started at file1.c, then jumped to
file2.c, file3.h, file4.c, and so on, until I forgot that I started at <code>file1.c</code>
(<code>file1.c</code> can be a long and hard to remember name). It makes me want to do this
whole code hopping process in another separated frame/buffer instead of messing
with my current buffer. I tried improved the process:
</p>
<ul class="org-ul">
<li><b>Using a different buffer</b>: Initially, I create another buffer and start from
there. However, it is usually the case that the other buffer is also a useful buffer.</li>
<li><b>Using a different workspace</b>: I am using <a href="https://github.com/wasamasa/eyebrowse">eyebrowse</a>, a package that can create a
whole new workspace and save the previous window configuration as another
workspace. Effectively, you can switch between different window configurations
with ease. This solution quickly becomes cumbersome, because I must remember
which workspace is for browsing code, not to mention it is quite common for me
to create 5 other workspaces for other purposes. It quickly becomes a burden
to manage the workspaces.</li>
</ul>
<p>
It is at this point that I suddenly remember frames. That's right, Emacs frames!
It is perfect for this use case. I can do whatever I want in this frame, and
when done, simply close it with <code>C-x 5 0</code>. With frames, the number of my
workspaces (using eyebrowse) is kept at a manageable number.
</p>
<p>
But wait, if an Emacs frame is small enough, isn't it the same as a popup
window, but with every feature of a buffer (syntax highlighting, code jumping,
etc) available? Not to mention, making a frame is much more lightweight than
other popup solutions.
</p>
<p>
At this point, implementing a peek definition in Emacs is
simply automating these steps:
</p>
<ol class="org-ol">
<li>Find the absolute position of the current beginning of the symbol at point,
in pixels.</li>
<li>Create a new invisible frame, with the current buffer in it.</li>
<li>Position the new frame right under the beginning of the symbol at point.</li>
<li>Jump to the symbol at point.</li>
<li>Make frame visible again.</li>
</ol>
<p>
That's all for a peek definition popup:
</p>
<div class="figure">
<p><a href="static/peek-definition-emacs.gif"><img src="static/peek-definition-emacs.gif" alt="peek-definition-emacs.gif" /></a>
</p>
</div>
<p>
In the example, I used <code>rtags-find-symbol-at-point</code> function for jumping. But
you can use any function that finds a definition, as long as it jumps to a
buffer. Finally, here is the code:
</p>
<div class="org-src-container">
<pre class="src src-emacs-lisp">(<span style="color: #0000FF;">defun</span> <span style="color: #006699;">rtags-peek-definition</span> ()
<span style="color: #036A07;">"Peek at definition at point using rtags."</span>
(<span style="color: #0000FF;">interactive</span>)
(<span style="color: #0000FF;">let</span> ((func (<span style="color: #0000FF;">lambda</span> ()
(rtags-find-symbol-at-point)
(rtags-location-stack-forward))))
(rtags-start-process-unless-running)
(make-peek-frame func)))
(<span style="color: #0000FF;">defun</span> <span style="color: #006699;">make-peek-frame</span> (find-definition-function <span style="color: #6434A3;">&rest</span> args)
<span style="color: #036A07;">"Make a new frame for peeking definition"</span>
(<span style="color: #0000FF;">when</span> (<span style="color: #0000FF;">or</span> (not (<span style="color: #0000FF;">rtags-called-interactively-p</span>)) (rtags-sandbox-id-matches))
(<span style="color: #0000FF;">let</span> (summary
doc-frame
x y
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
<span style="color: #8D8D84;">;; </span><span style="color: #8D8D84; font-style: italic;">1. Find the absolute position of the current beginning of the symbol at point, ;;</span>
<span style="color: #8D8D84;">;; </span><span style="color: #8D8D84; font-style: italic;">in pixels. ;;</span>
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
(abs-pixel-pos (<span style="color: #0000FF;">save-excursion</span>
(beginning-of-thing 'symbol)
(window-absolute-pixel-position))))
(<span style="color: #0000FF;">setq</span> x (car abs-pixel-pos))
<span style="color: #8D8D84;">;; </span><span style="color: #8D8D84; font-style: italic;">(setq y (cdr abs-pixel-pos))</span>
(<span style="color: #0000FF;">setq</span> y (+ (cdr abs-pixel-pos) (frame-char-height)))
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
<span style="color: #8D8D84;">;; </span><span style="color: #8D8D84; font-style: italic;">2. Create a new invisible frame, with the current buffer in it. ;;</span>
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
(<span style="color: #0000FF;">setq</span> doc-frame (make-frame '((minibuffer . nil)
(name . <span style="color: #008000;">"*RTags Peek*"</span>)
(width . <span style="color: #D0372D;">80</span>)
(visibility . nil)
(height . <span style="color: #D0372D;">15</span>))))
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
<span style="color: #8D8D84;">;; </span><span style="color: #8D8D84; font-style: italic;">3. Position the new frame right under the beginning of the symbol at point. ;;</span>
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
(set-frame-position doc-frame x y)
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
<span style="color: #8D8D84;">;; </span><span style="color: #8D8D84; font-style: italic;">4. Jump to the symbol at point. ;;</span>
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
(<span style="color: #0000FF;">with-selected-frame</span> doc-frame
(apply find-definition-function args)
(read-only-mode)
(<span style="color: #0000FF;">when</span> semantic-stickyfunc-mode (semantic-stickyfunc-mode <span style="color: #D0372D;">-1</span>))
(recenter-top-bottom <span style="color: #D0372D;">0</span>))
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
<span style="color: #8D8D84;">;; </span><span style="color: #8D8D84; font-style: italic;">5. Make frame visible again ;;</span>
<span style="color: #8D8D84;">;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;</span>
(make-frame-visible doc-frame))))
</pre>
</div>
<p>
Then, bind the new command to a key and try it out:
</p>
<div class="org-src-container">
<pre class="src src-emacs-lisp">(global-set-key (kbd <span style="color: #008000;">"C-c p"</span>) 'rtags-peek-definition)
</pre>
</div>
<p>
To close the peek frame, simply use <code>C-x 5 0</code> (runs <code>delete-frame</code> command). You
can bind it to another key to close frame easier, e.g. <code>f12</code> key.
</p>
<p>
The more I use Emacs, the more I start realizing how useful frames
are. Especially with Emacs 26 onward, there is an option to remove a frame from
OS taskbar, effectively you cannot use Alt+Tab to switch to any child frame
created in Emacs. With this feature, you can create many Emacs frames without
creating a mess that renders Alt+tab unusable. Perhaps it is the time to embrace
the frames.
</p>
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