Support of Eight Scan panels (8 rows in a frame)

[board707]

Working with matrices sometimes I come across panels that in the @mrcodetastic's accepted terminology (by analogy with quarter scan panels) should be called eight scans.
No need to confuse them with panels with a scan of 1/8, I mean the case when eight lines are simultaneously illuminated in each frame - for example 64x32 1/4 or like the panel 32x16 1/2 below:

see the label:

Basicly, working with such panels using the VirtualMatrixPanel class is similar to quarter scan panels, only in this case we use virtual coordinates stretched along the x-axis by 4 times and compressed by the same amount along the y-axis:

HUB75_I2S_CFG mxconfig(
    PANEL_RES_X * 4,            // DO NOT CHANGE THIS
    PANEL_RES_Y / 4,            // DO NOT CHANGE THIS
    NUM_ROWS * NUM_COLS         // DO NOT CHANGE THIS
    //,_pins            // Uncomment to enable custom pins
  );

And we will need more sophisticated pixel mapping, because we have to describe the distribution of pixels across 4 rows. The mapping of my panel can be schematically described as follows (first and third row in a frame goes from right to left, 2nd and 4th - in opposite, the pixel base is 8 pixels);

<<<<<<<< 
>>>>>>>>
<<<<<<<<
>>>>>>>> 

After some thought, I described it in the getCoords() method as follows:

inline VirtualCoords CustomPxBasePanel ::getCoords(int16_t x, int16_t y) {

  coords = VirtualMatrixPanel::getCoords(x, y); // call base class method to update coords for chaining approach

  if ( coords.x == -1 || coords.y == -1 ) { // Co-ordinates go from 0 to X-1 remember! width() and height() are out of range!
    return coords;
  }

  uint8_t pxbase = 8;  // pixel base
  uint8_t mult_row = (coords.y / 2) % 4; //row order number in the frame

  if (mult_row % 2) {  
    coords.x = (coords.x / pxbase) * 4 * pxbase  + mult_row * pxbase    +  (coords.x & 0x7);
  }
  else {
    coords.x = (coords.x / pxbase) * 4 * pxbase  + mult_row * pxbase    +  7 - (coords.x & 0x7);
  }

  coords.y = (coords.y / 8) * 2 + (1 - (coords.y & 1));

  return coords;
}

These settings allowed me to get the correct display of pixels on the panel.

I hope this will be useful to someone.