I want to see if the littlevgl GUI library can be used on my camera to provide a GUI on top-of and around the video stream.  One great thing about this library is a well-defined hardware abstraction layer that already includes support for the linux frame buffer and linux touchscreen event driver.  I already had the frame buffer running on my LCD module and I finally figured out how to use the LCD's resistive touch controller with new device tree entries.  This allowed me to quickly get the littlevgl demo program running.

littlevgl also has a direct SPI-based driver for the TSC2046 resistive touch controller IC that I originally thought I might use.  Typically this would be used on a bare-metal embedded system (such as an Arduino or Teensy).  However as I researched it became clear that using the built-in linux touchscreen driver would be superior because I could make use of tslib's ability to provide calibration and de-jitter for the resistive touchscreen.  I did have to make a hardware change and add the pendown IRQ to a GPIO (GPIO27/P2.19) on the Pocketbeagle so my wiring diagram is updated.

Architecturally the system looks as follows.  The tslib utility program ts_calibrate is run before the application to generate the pointercal file used subsequently by the daemon.

The resistive touch screen works fairly well and will probably be sufficient for my application but we are spoiled by our capacitive touch screens and using something like the Adafruit Cap Touch LCD Module would eliminate the need for tslib and provide much better control at a substantial increase in cost (USD14 -> USD45).

The updated device tree files, uEnv.txt and configured littlevgl library and demo are available on github.  I also got this running on a Beaglebone Black.  Even if you never build this camera perhaps the ability to have a sophisticated GUI running on a cheap LCD without needing the entire window system might be useful.