// squash all the modes for this demo
unsigned char appleToGhettoVGA(unsigned char apple) {
  if(apple >= 0xC0) return apple-0x40;
  else return apple&0x7F;
}

// Squash into normal mode
unsigned char ghettoVGAToApple(unsigned char ghettoVga) {
  if(ghettoVga >= 0x40 && ghettoVga <= 0x7f) return ghettoVga; 
  else return ghettoVga|0x80;
}

// Extract row, column addressing from woz's interlacing mode
static unsigned char g_row = 0, g_col = 0;
void decodeScreenAddress(unsigned short address) {
  unsigned char block_of_lines = (address>>7) - 0x08;
  unsigned char block_offset = (address&0x00FF) - ((block_of_lines&0x01) ? 0x80 : 0x00);
  if(block_offset < 0x28) {
    g_row = block_of_lines;
    g_col = block_offset;
  } else if(block_offset < 0x50) {
    g_row = block_of_lines + 8;
    g_col = block_offset-0x28;
  } else {
    g_row = block_of_lines + 16;
    g_col = block_offset-0x50;
  }
}

unsigned char screenRead(unsigned short address) {
    //Find our row/column
  decodeScreenAddress(address);
  return ghettoVGAToApple(readCharacter(g_row, g_col));
}

void screenWrite(unsigned short address, unsigned char value) {
  //Find our row/column
  decodeScreenAddress(address);
  // If not bell character
  if(value != 0x87) writeCharacter(g_row, g_col, appleToGhettoVGA(value));
}