UG8lib bitmap understanding

So after two weeks I finally got my 128*64 dot matrix display to function using the UG8lib. inside the example code provided with the library is one called Bitmap provided below for convenience. Now what I wish to understand is how would one write a an image into it for display? examples being game sprites like sonic or mario, again for example and practice. can someone explain it at all? I understand its binary conversion, not unlike writing for a commodore 64, but I personally never learned how to do that, anyway any advice would be greatly appreciated.

/*

  Bitmap.pde
  
  Show simple bitmap

  >>> Before compiling: Please remove comment from the constructor of the 
  >>> connected graphics display (see below).

  Universal 8bit Graphics Library, https://github.com/olikraus/u8glib/
  
  Copyright (c) 2011, olikraus@gmail.com
  All rights reserved.

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*/


#include "U8glib.h"

// setup u8g object, please remove comment from one of the following constructor calls
// IMPORTANT NOTE: The following list is incomplete. The complete list of supported 
// devices with all constructor calls is here: https://github.com/olikraus/u8glib/wiki/device

U8GLIB_ST7920_128X64_1X u8g(12, 10, 11); // SPI Com: SCK = en = 18, MOSI = rw = 16, CS = di = 17
//U8GLIB_ST7920_128X64_4X u8g(18, 16, 17); // SPI Com: SCK = en = 18, MOSI = rw = 16, CS = di = 17
//U8GLIB_ST7920_192X32_1X u8g(8, 9, 10, 11, 4, 5, 6, 7, 18, 17, 16);   // 8Bit Com: D0..D7: 8,9,10,11,4,5,6,7 en=18, di=17,rw=16
//U8GLIB_ST7920_192X32_4X u8g(8, 9, 10, 11, 4, 5, 6, 7, 18, 17, 16);   // 8Bit Com: D0..D7: 8,9,10,11,4,5,6,7 en=18, di=17,rw=16
//U8GLIB_ST7920_192X32_1X u8g(18, 16, 17); // SPI Com: SCK = en = 18, MOSI = rw = 16, CS = di = 17

const uint8_t rook_bitmap[] PROGMEM = {
  0x00,         // 00000000 
  0x55,         // 01010101
  0x7f,          // 01111111
  0x3e,         // 00111110
  0x3e,         // 00111110 
  0x3e,         // 00111110
  0x3e,         // 00111110 
  0x7f           // 01111111
};

void draw(void) {
  // graphic commands to redraw the complete screen should be placed here  
  u8g.drawBitmapP( 0, 0, 1, 8, rook_bitmap);
}

void setup(void) {
}

void loop(void) {
  // picture loop
  u8g.firstPage();  
  do {
    draw();
  } while( u8g.nextPage() );
  
  // rebuild the picture after some delay
  delay(1000);
}

I've never used UG8lib, but other OLED libraries I've tried, use XBMs (X BitMaps).
You can easily use GIMP to export an image to XBM.
Pieter

unfortunately the display I use has no support for a SD card or microSD, though I'm sure an SD card shield would remedy that, but for that to work I'd need another library (for sanity's sake) that supports an LCD using the ST7920 chipset

You don't need an SD card, it's a C array, you can just save it to progmem (that's what they do in the example you posted).

Pieter