This is the PatternPlasma Demo adopted for use with multiple LED Matrix Panel displays arranged in a non standard order (i.e. a grid) to make a bigger display.
When you link / chain multiple panels together, the ESP32-HUB75-MatrixPanel-I2S-DMA library treats as one wide horizontal panel. This would be a 'standard' (default) order.
Non-standard order is essentially the creation of a non-horizontal-only display that you can draw to in the same way you would any other display, with VirtualDisplay library looking after the pixel mapping to the physical chained panels.
For example: You bought four (4) 64x32px panels, and wanted to use them to create a 128x64pixel display. You would use the VirtualMatrixPanel class.
3. In your Arduino sketch, use the 'VirtualMatrixPanel' class instance (virtualDisp) to draw to the display (i.e. drawPixel), instead of the underling MatrixPanel_I2S_DMA class instance (dma_display).