Investigate byte swapping requirement for ILI9341 display controller

[ajlennon]

Background

Currently, the ESP-IDF display driver swaps bytes for each pixel to match TFT_eSPI's behavior when pushColors is called with swap=true. This byte swapping is done in software in the flush function.

Investigation Needed

1. Is byte swapping required?

   • Check if the ILI9341 display controller or the specific display module requires byte swapping
   • Determine if this is a hardware requirement or just matching TFT_eSPI's behavior
   • Test if removing byte swapping causes color issues

2. Performance Optimization

   • Byte swapping is currently done in software for every pixel, which adds CPU overhead
   • Investigate if we can:
     • Configure the display controller to accept native byte order (avoid swapping)
     • Use hardware features (DMA, SPI) to handle byte swapping
     • Optimize the byte swap operation (SIMD, lookup tables, etc.)
     • Pre-swap image data during conversion instead of runtime

3. Image Display Performance

   • Current implementation swaps bytes during flush, which happens for every LVGL refresh
   • Consider pre-swapping image data during PNG to RGB565 conversion
   • This would eliminate runtime byte swapping for static images (logos, splashscreen)

Related Code

• src/lvgl_display.cpp: lvgl_display_flush() function performs byte swapping
• tools/convert_logo.py: Image conversion script (could be modified to pre-swap bytes)

Expected Outcome

Determine the most efficient approach:

• If byte swapping is required: optimize the swap operation or move it to image conversion
• If byte swapping is not required: remove it to improve performance