<p>I submitted the following to the Debian bug tracker
<a href="https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=931305">#931305</a>.</p>

<hr />

<p>While using proportional fonts, the Greek letter pi (π) is treated as
a box-drawing character or, more likely, as missing from the
proportional font altogether.  This happens <em>only at certain point
sizes</em> AND/OR <em>only with specific fonts</em>.</p>

<h2>Scenario 1: Greek pi works, but box-drawing does not</h2>

<p>With these settings:</p>

<pre><code>xterm.vt100.faceName: DejaVu Sans Mono
xterm.vt100.faceSize: 10
XTerm.vt100.forceBoxChars: false
</code></pre>

<p>The greek letter pi is displayed correctly, but the second vertical line
(drawn with U+2502) is almost the same as the first one (drawn with
U+007C).</p>

<p><img alt="image scenario 1" src="https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario1.png" /></p>

<h2>Scenario 2: Greek pi does not work, but box-drawing does</h2>

<p>With these settings:</p>

<pre><code>xterm.vt100.faceName: DejaVu Sans Mono
xterm.vt100.faceSize: 10
XTerm.vt100.forceBoxChars: true
</code></pre>

<p>The Greek letter pi is drawn using a fixed-size (bitmap) font.  The
second vertical line is properly displayed using box-drawing characters.</p>

<p><img alt="image scenario 2" src="https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario2.png" /></p>

<h2>Scenario 3: faceSize: 9.5 forceBoxChars: false works for both</h2>

<p>With these settings:</p>

<pre><code>xterm.vt100.faceName: DejaVu Sans Mono
xterm.vt100.faceSize: 9.5
XTerm.vt100.forceBoxChars: false
</code></pre>

<p>Everything appears to work as intended.</p>

<p><img alt="image scenario 3" src="https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario3.png" /></p>

<h2>Scenario 4: Fira Code works using settings from scenarios 1 and 3</h2>

<p>With these:</p>

<pre><code>xterm.vt100.faceName: Fira Code
xterm.vt100.faceSize: 10
XTerm.vt100.forceBoxChars: false
</code></pre>

<p>Or this changed:</p>

<pre><code>xterm.vt100.faceSize: 9.5
</code></pre>

<p>Everything seems to work as intended.</p>

<p><img alt="image scenario 4" src="https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario4.png" /></p>

<h2>Scenario 5: forceBoxChars always breaks Greek letter pi (π)</h2>

<p>With these settings:</p>

<pre><code>xterm.vt100.faceName: Fira Code
xterm.vt100.faceSize: 10
XTerm.vt100.forceBoxChars: true
</code></pre>

<p>Regardless of typeface, enabling forceBoxChars will always draw the
letter pi in a bitmap font.</p>

<p><img alt="image scenario 5" src="https://protesilaos.com/assets/images/attachments/xterm_grpi_boxchars_scenario5.png" /></p>