LilyGo : Load Images from SD Card

 My LilyGo Genius Remote (smarter than a smart remote) is becoming more sophisticated as I investigate and utilise extra features.  It almost seems strange that I haven't used the SD card previously as programming in the non-Arduino world is often pre-occupied with files.
Lily comes with a demo sketch SD_Test which shows file and directory functions on an SD card so it was an easy matter to incorporate the SD card into my sketch and list / read  files.

As Lily has a small graphics screen, the factory_test demo sketch displays a logo as Lily starts up.  Data for the picture is provided by a header file in the demo sketch containing pixel values which are compiled with the sketch and loaded into a flash memory (PROGMEM) array so they can be displayed using the displayWrite method in the TFT_eSPI library.

To make my own picture I can use a utility program ImageConverter 565 . The screen size is 240w x 135h so my first step is to find an image and, using MS Paint, cut it down to 240 x 135 pixels, which is a rectangular shape.  ImageConvertor will the convert it to C format which is a statement defining a PROGMEM array with 32,400 16 bit data values.  I include this file as a header within my sketch and can then display it on the screen.

I potentially want to display a variety of pictures on the small screen so I would prefer to load the images from my SD card at run-time rather than compile and download them in a sketch.  ImageConverter can also create images in a ".raw" file format. The screen size is 240w x 135h and each pixel is 16 bits.  The RAW file contains no header or format information, just the pixels, so the file created is exactly 240 x 135 x 2 bytes = 64,800 bytes.

I remove the SD card from Lily and copy my image files on to it.  I like the fact that it is exactly 64,800 bytes, nothing at all is added to the file.  To load the image I simply have to read the file into an array and display it.  The ScreenBuffer array is 32,400 bit values so I have to read in two bytes to each array element.  I can then load an image whenever I want.

I cant stress enough what a wonderful hardware package LilyGo is for ESP32 development.  I think LilyGo are a maker / hobbyist company, but this device is potential usable in shops as a hand-held terminal.  I hope that this box or a similar one continues to be available.  As an added bonus the demo sketches show you how to use all the functions so you don't have to spend time looking for datasheets, pin numbers, libraries etc; making it childsplay to provide more functions.  I love it.