title: Running Qt 5.15 GUI app on Pi 4 with TFT screen
body: <p>I have a Raspberry Pi 4 with an TFT touchscreen. I downloaded the raspbian image with drivers for the screen installed and the screen displays the desktop.
  I would develop applications with Qt for it. So I cross-compiled Qt 5.15.2.</p>
  <p>Now when I run the app, the error is :</p>
  <pre><code>&quot;Could not find DRM device!&quot;.
  </code></pre>
  <p>In the screen datasheet, it's mentionned to disable the DRM VC4 V3D driver (already done in the pre-installed image).</p>
  <p>I tried to launch the app with &quot;-platform linuxfb&quot; and the app is shown on the screen, but when I touch it, the desktop is re-draw on the top of it (writing on the same buffer /dev/fb0 ?).</p>
  <p>How can I configure my rasberry pi to run qt gui app correctly ?</p>
  <p>Regards</p>
  <p>Stéphane</p>
  <hr />
  <p>Qt :</p>
  <pre><code>5.15.2
  </code></pre>
  <p>Linux:</p>
  <pre><code>Distributor ID: Raspbian
  Description:    Raspbian GNU/Linux 10 (buster)
  Release:        10
  Codename:       buster
  </code></pre>
  <p>Links :
  <a href="https://joy-it.net/files/files/Produkte/RB-TFT3.5/RB-TFT-Manual_04082020.pdf" rel="nofollow noreferrer">TFT Screen</a></p>