8bitworkshop/presets/atari7800/scroll.c

#include "atari7800.h"

#include <string.h>

//#link "chr_font.s"

//#link "generic8x16.s"

#define DLL_FLAGS DLL_H16
#define SLOTHEIGHT 16
#define SLOTSIZE 32
#define DOUBLEBUFFER
#define DLSAVE

#ifdef DOUBLEBUFFER
#define NUMSLOTS 32
byte slot0 = 0;
#else
#define NUMSLOTS 16
const byte slot0 = 0;
#endif


DLLEntry DLL[NUMSLOTS];

byte DL[NUMSLOTS][SLOTSIZE];
byte DL_len[NUMSLOTS];

#ifdef DLSAVE
byte DL_save[NUMSLOTS];
#endif

void dll_set_addr(const void* dpp) {
  MARIA.DPPH = (word)dpp>>8;
  MARIA.DPPL = (byte)dpp;
}

void dll_clear() {
  byte i;
  for (i=slot0; i<slot0+16; i++) {
    DL_len[i] = 0;
    DL[i][1] = 0;
  }
}

#ifdef DLSAVE
void dll_save() {
  memcpy(DL_save, DL_len, sizeof(DL_save));
}

void dll_restore() {
  byte i;
  memcpy(DL_len, DL_save, sizeof(DL_save));
  for (i=0; i<NUMSLOTS; i++) {
    DL[i][DL_len[i]+1] = 0;
  }
}
#endif

#ifdef DOUBLEBUFFER
void dll_swap() {
  slot0 ^= 16;
  if (!slot0) {
    dll_set_addr(DLL+16);
  } else {
    dll_set_addr(DLL);
  }
}

void dll_set_scroll(byte y) {
  static byte oldslot = 0;
  byte slot = y / SLOTHEIGHT;
  byte offset = 15 - (y & 15);
  DLL[oldslot].offset_flags = DLL_FLAGS | (SLOTHEIGHT-1);
  DLL[slot].offset_flags = DLL_FLAGS | offset;
  dll_set_addr(DLL + slot);
  oldslot = slot;
}
#endif

void* dll_alloc(byte slot, byte len) {
  byte dlofs;
  slot &= NUMSLOTS-1;
  dlofs = DL_len[slot];
  DL_len[slot] += len;
  DL[slot][dlofs+len+1] = 0;
  return &DL[slot][dlofs];
}

void dll_add_sprite(word addr, byte x, byte y, byte wpal) {
  byte slot = (y / SLOTHEIGHT) | slot0;
  register DL4Entry* dl = (DL4Entry*) dll_alloc(slot, 4);
  dl->data_lo = (byte)addr;
  dl->data_hi = (byte)(addr>>8) + (y & 15);
  dl->xpos = x;
  dl->width_pal = wpal;
  if (y & 15) {
    DL4Entry* dl2 = (DL4Entry*) dll_alloc(slot+1, 4);
    *dl2 = *dl;
    dl2->data_hi -= SLOTHEIGHT;
  }
}

void dll_add_string(const char* str, byte x, byte y, byte wpal) {
  byte slot = (y / SLOTHEIGHT) | slot0;
  register DL5Entry* dl = (DL5Entry*) dll_alloc(slot, 5);
  dl->data_lo = (byte)str;
  dl->data_hi = (word)str>>8;
  dl->flags = DL5_INDIRECT;
  dl->width_pal = wpal;
  dl->xpos = x;
}

void dll_setup() {
  byte i;
  byte* dlptr = &DL[0][0];
  register DLLEntry *dll = &DLL[0];
  for (i=0; i<NUMSLOTS; i++) {
    dll->offset_flags = DLL_FLAGS | (SLOTHEIGHT-1);
    dll->dl_hi = (word)dlptr>>8;
    dll->dl_lo = (byte)dlptr;
    dlptr += sizeof(DL[0]);
    dll++;
  }
  dll_clear();
#ifdef DOUBLEBUFFER
  dll_swap();
  dll_clear();
  dll_swap();
#endif
#ifdef DLSAVE
  memset(DL_save, 0, sizeof(DL_save));
#endif
}

char* hello = "\2\4\6\0\220\222\102";

void main() {
  byte i;
  byte y = 0;

  dll_setup();
  
  // activate DMA
  MARIA.CHARBASE = 0x80;
  MARIA.P0C1 = 0x8f;
  MARIA.P0C2 = 0x4f;
  MARIA.P0C3 = 0x1f;
  MARIA.P1C1 = 0x34;
  MARIA.P1C2 = 0x28;
  MARIA.P1C3 = 0x1f;
  MARIA.BACKGRND = 0;
  dll_set_addr(DLL);
  MARIA.CTRL = CTRL_DMA_ON | CTRL_DBLBYTE | CTRL_160AB;

  dll_clear();
  dll_add_string(hello, y+32, 32, DL_WP(8,0));
  for (i=0; i<8; i++) {
    slot0 = 0;
    dll_add_sprite(0xa068, i*4, i*33, DL_WP(4,1));
    dll_add_sprite(0xa06c, i*8, i*25, DL_WP(4,1));
    slot0 = 16;
    dll_add_sprite(0xa068, i*4, i*32, DL_WP(4,1));
    dll_add_sprite(0xa06c, 128-i*8, i*24, DL_WP(4,1));
  }
  dll_save();

  while (1) {
    while ((MARIA.MSTAT & MSTAT_VBLANK) == 0) ;
    dll_set_scroll(y);
    dll_restore();
    dll_add_sprite(0xa06c, y, y, DL_WP(4,1));
    while ((MARIA.MSTAT & MSTAT_VBLANK) != 0) ;
    y++;
  }
}