GBA Scroll (Wrap)

#include <gba.h>

// These are your tiles and map data
#include "graphics.h"
#include "map.h"

static void updateBGColumn(u16 column)
{
  const u16* src = (const u16*) map;
  u16* dst = (u16*) SCREEN_BASE_BLOCK(16);
  u16 updateX = (column + 32) % 32 - 1;
  if (updateX > 0)
  {
    for (u16 j = 0; j < 32; ++j)
    {
       dst[y * 32 + updateX] = src[y * mapWidth + updateX + 32];
    }
  }
}

int main(void)
{
  // Load the palette
  CpuSet(bg_palette,
         BG_PALETTE,
         COPY16 | bg_palette_size / 2);

  // Load the tiles into VRAM, Char Block 0
  CpuSet(tiles, CHAR_BASE_BLOCK(0), COPY16 | tiles_size / 2);

  // Load the first chunk of our map
  const u16* src = (const u16*) map;
  u16* dst = (u16*) SCREEN_BASE_BLOCK(16);

  for (u16 j = 0; j < 32; ++j)
  {
    for (u16 i = 0; i < 32; ++i)
    {
       dst[j * 32 + i] = src[j * map_width + i];
    }
  }

  SetMode(MODE_0 | BG0_ENABLE);

  irqInit();
  irqEnable(IRQ_VBLANK);

  u16 delay = 0;
  u16 xScroll = 0;
  u16 mapX = 0;

  while (true)
  {
    VBlankIntrWait();

    if (delay++ % 10 == 0)
    {
      xScoll++;

      if (++xScroll % 8 == 0)
      {
        mapX += 1;
        updateBGColumn(mapX);
      }

      BG0HOFS = xScroll;
    }
  }

  return 0;
}