void BlitFirstPlaneFirstRowToSecondRow(struct ScreenSetup *screenSetup) {
  unsigned char *source = screenSetup->memoryStart;
  unsigned char *target = (screenSetup->memoryStart + SCREEN_WIDTH * 2 / 8);

  custom.bltcon0 = 0x09f0;
  custom.bltcon1 = 0;
  custom.bltapt = source;
  custom.bltdpt = target;
  custom.bltamod = 0;
  custom.bltdmod = 0;
  custom.bltafwm = 0xffff;
  custom.bltalwm = 0xffff;
  custom.bltsize = 0x0041;
}

void BlitShiftFirstPlaneFirstRowToThirdRow(struct ScreenSetup *screenSetup) {
  unsigned char *source = screenSetup->memoryStart;
  unsigned char *target = (screenSetup->memoryStart + SCREEN_WIDTH * 4 / 8);

  custom.bltcon0 = 0x49f0;
  custom.bltcon1 = 0;
  custom.bltapt = source;
  custom.bltdpt = target;
  custom.bltamod = 0;
  custom.bltdmod = 0;
  custom.bltafwm = 0xffff;
  custom.bltalwm = 0xffff;
  custom.bltsize = 0x0041;
}

void BlitWithMaskInBChannel(struct ScreenSetup *screenSetup) {
  unsigned char *source = screenSetup->memoryStart;
  unsigned char *target = (screenSetup->memoryStart + SCREEN_WIDTH * 6 / 8);
  unsigned char *mask = (screenSetup->memoryStart + 8);

  // a is source
  // b is mask
  // d is destination

  // so I want AB

  custom.bltcon0 = 0x0dc0;
  custom.bltcon1 = 0;
  custom.bltapt = mask;
  custom.bltbpt = source;
  custom.bltdpt = target;
  custom.bltamod = 0;
  custom.bltdmod = 0;
  custom.bltafwm = 0xffff;
  custom.bltalwm = 0xffff;
  custom.bltsize = 0x0041;
}

void BlitWithMaskInBDataInCChannel(struct ScreenSetup *screenSetup) {
  unsigned char *source = screenSetup->memoryStart;
  unsigned char *target = (screenSetup->memoryStart + SCREEN_WIDTH * 8 / 8);
  unsigned char *mask = (screenSetup->memoryStart + 8);
  unsigned char *background = (screenSetup->memoryStart + 16);

  // a is source
  // b is mask
  // c is background
  // d is destination

  // so I want AB+`AC

  custom.bltcon0 = 0x0fca;
  custom.bltcon1 = 0;
  custom.bltapt = mask;
  custom.bltbpt = source;
  custom.bltcpt = background;
  custom.bltdpt = target;
  custom.bltamod = 0;
  custom.bltbmod = 0;
  custom.bltcmod = SCREEN_WIDTH / 8;
  custom.bltdmod = SCREEN_WIDTH / 8;
  custom.bltafwm = 0xffff;
  custom.bltalwm = 0xffff;
  custom.bltsize = 0x0041;
}

void BlitDrawHorizontalLine(struct ScreenSetup *screenSetup) {

  // i want to draw a line from 20,20 to 50,80
  // i need to get dx and dy
  // dx is 30, dy is 60
  // the shift value is 20 mod 15 = 5
  // a data register gets $8000
  // b data register gets $ffff
  // text shift is 0
  // c and d pointers get the word containing the first pixel, so
  //   screenSetup->memoryStart + 320 * 20 / 8 + 2
  // module registers get width of bitplane in bytes
  // blit height is dx + 1 so 31
  // blit width = 2
  // logic is ab+'a, so 6, 7, 2, 3, 1, 0

  char *target = screenSetup->memoryStart + (320 * 20 + 20) / 8;
  int dx = 10;
  int dy = 60;
  int tmp;

  if (dx < dy) {
    tmp = dx;
    dx = dy;
    dy = tmp;
  }

  custom.bltcon0 = (5 << 12) + (11 << 8) + 0xca;
  custom.bltcon1 = 1;
  custom.bltapt = 4 * dy - 2 * dx;
  custom.bltadat = 0x8000;
  custom.bltbdat = 0xffff;
  custom.bltcpt = target;
  custom.bltdpt = target;
  custom.bltamod = 4 * (dy - dx);
  custom.bltbmod = 4 * dy;
  custom.bltcmod = 320 / 8;
  custom.bltdmod = 320 / 8;
  custom.bltafwm = 0xffff;
  custom.bltalwm = 0xffff;
  custom.bltsize = 0x02 + (dx + 1 << 7);
}