system/vncviewer: add VNC viewer for LCD display

[JianyuWang0623]

Summary

Add examples/vncviewer — a lightweight VNC viewer that renders a remote desktop on an LCD display via the NuttX LCD character device interface (/dev/lcd0).

• RFB 3.8 protocol with VNC Authentication (pure software DES, no external library)
• Auto-detect pixel format from LCD driver
• Raw encoding with row-by-row rendering — minimal RAM usage
• Automatic reconnection on disconnect
• CLI: vncviewer [-p password] [-d lcd_devno] <host> [port]

Tested on ESP32-S3 (lckfb-szpi-esp32s3) with ST7789 320×240 SPI LCD over WiFi. Board-side defconfig will be submitted separately to nuttx repo.

Impact

New example application only. No impact on existing code.

Testing

• Host: Ubuntu 22.04 x86_64, xtensa-esp-elf-gcc
• Target: lckfb-szpi-esp32s3 (ESP32-S3-WROOM-1-N16R8), ST7789 320×240 LCD
• VNC server: x11vnc on Ubuntu
• vncviewer (Device): vncviewer -p mypasswd xxx.xxx.xxx.xxx 5901
• vncviewer (Host): vncviewer localhost:5901 & # Enter password in the UI

Three server modes verified:

1. Xvfb virtual desktop (:1, 320×240x16 + openbox + xterm) — pixel-perfect 1:1

# vncserver (Host)
Xvfb :1 -screen 0 320x240x16 &
DISPLAY=:1 openbox &
DISPLAY=:1 xterm -geometry 38x11+0+0 -fa Monospace -fs 10 -T bash -e 'bash --rcfile /tmp/vnc-bashrc' &
x11vnc -display :1 -rfbport 5901 -passwd mypasswd -shared -forever -xkb -add_keysyms -bg

2. Physical desktop clip (-clip 320x240+0+0) — top-left region, no scaling

# vncserver (Host)
x11vnc -display :0 -rfbport 5901 -passwd mypasswd -shared -forever -xkb -add_keysyms -bg -clip 320x240+0+0

3. Physical desktop scale (-scale 320x240) — full desktop scaled to LCD

# vncserver (Host)
x11vnc -display :0 -rfbport 5901 -passwd mypasswd -shared -forever -xkb -add_keysyms -bg -scale 320x240

[cederom]

Wow! This is amazing big thank you @JianyuWang0623 :-)

I am wondering if this should go to apps/examples or better to apps/system ? :-)

[acassis]

@JianyuWang0623 WOW!!!

[JianyuWang0623]

Wow! This is amazing big thank you @JianyuWang0623 :-)

I am wondering if this should go to apps/examples or better to apps/system ? :-)

Either way works for me. I'll go with whatever you all think is better. :-)

[cederom]

What do you think folks? I think this tool suits better to apps/system right? :-)

[lupyuen]

Sorry @raiden00pl: Install NTFC is failing at git clone, could you retry if it fails? Then sync it to NuttX Repo and NuttX Apps Repo? (NuttX Apps is missing the pip install ntfc retry) Thanks :-) FYI @simbit18

https://github.com/apache/nuttx-apps/actions/runs/24843435684/job/72727760891#step:10:134

$ git clone -b release-0.0.1 https://github.com/szafonimateusz-mi/nuttx-testing
fatal: unable to access 'https://github.com/szafonimateusz-mi/nuttx-testing/': The requested URL returned error: 500

[JianyuWang0623]

What do you think folks? I think this tool suits better to apps/system right? :-)

@cederom Moved to apps/system.

[cederom]

What do you think folks? I think this tool suits better to apps/system right? :-)

@cederom Moved to apps/system.

TANK U SIR @JianyuWang0623 ! =)

[cederom]

Thank you @JianyuWang0623 awesome stuff! =)

[acassis]

@JianyuWang0623 please include Documentation with the host vcnserver/Xvfb configuration example (please include at least the first two pictures)