8bitworkshop/presets/nes/horizmask.c

#include "neslib.h"
#include <string.h>

// 0 = horizontal mirroring
// 1 = vertical mirroring
#define NES_MIRRORING 1

// VRAM update buffer
#include "vrambuf.h"
//#link "vrambuf.c"

// link the pattern table into CHR ROM
//#link "chr_generic.s"

// function to write a string into the name table
//   adr = start address in name table
//   str = pointer to string
void put_str(unsigned int adr, const char *str) {
  vram_adr(adr);        // set PPU read/write address
  vram_write(str, strlen(str)); // write bytes to PPU
}

word x_scroll;		// X scroll amount in pixels
byte bldg_height;	// building height in tiles
byte bldg_width;	// building width in tiles
byte bldg_char;		// character to draw
byte bldg_attr;		// attribute table value

#define PLAYROWS 24

word nt2attraddr(word a) {
  return (a & 0x2c00) | 0x3c0 |
    ((a >> 4) & 0x38) | ((a >> 2) & 0x07);
}

void new_building() {
  bldg_height = (rand8() & 7) + 2;
  bldg_width = (rand8() & 3) * 4 + 4;
  bldg_char = (rand8() & 15);
  bldg_attr = rand8();
}

void update_nametable() {
  register word addr;
  // a buffer drawn to the nametable vertically
  char buf[PLAYROWS];
  // divide x_scroll by 8
  // to get nametable X position
  byte x = ((x_scroll >> 3)+32) & 63;
  if (x < 32)
    addr = NTADR_A(x, 4);
  else
    addr = NTADR_B(x&31, 4);
  // clear empty space
  memset(buf, 0, PLAYROWS-bldg_height);
  // draw a random star
  buf[rand8() & 31] = '.';
  // draw roof
  buf[PLAYROWS-bldg_height-1] = bldg_char & 3;
  // draw rest of building
  memset(buf+PLAYROWS-bldg_height, bldg_char, bldg_height);
  // draw vertical slice in name table
  vrambuf_put(addr ^ 0xc000, buf, sizeof(buf));
  // every 4 columns, update attribute table
  if ((x & 3) == 1) {
    // compute attribute table address
    // of upper attribute block
    addr = nt2attraddr(addr) + 8*4;
    VRAMBUF_PUT(addr, bldg_attr, 0);
    // put lower attribute block
    addr += 8;
    VRAMBUF_PUT(addr, bldg_attr, 0);
    vrambuf_end();
  }
  // generate new building?
  if (--bldg_width == 0) {
    new_building();
  }
}

// function to scroll window up and down until end
void scroll_demo() {
  // make 1st building
  new_building();
  x_scroll = 0;
  // infinite loop
  while (1) {
    // update nametable every 8 pixels
    if ((x_scroll & 7) == 0) {
      update_nametable();
    }
    // manually force vram update
    // flush and clear VRAM buffer after NMI
    ppu_wait_nmi();
    flush_vram_update(updbuf);
    vrambuf_clear();
    // reset ppu address
    vram_adr(0x0);
    // set scroll register
    // and increment x_scroll
    split(x_scroll++, 0);
  }
}

/*{pal:"nes",layout:"nes"}*/
const char PALETTE[32] = { 
  0x03,			// background color

  0x25,0x30,0x27,0x00,	// ladders and pickups
  0x1C,0x20,0x2C,0x00,	// floor blocks
  0x00,0x10,0x20,0x00,
  0x06,0x16,0x26,0x00,

  0x16,0x35,0x24,0x00,	// enemy sprites
  0x00,0x37,0x25,0x00,	// rescue person
  0x0D,0x2D,0x1A,0x00,
  0x0D,0x27,0x2A	// player sprites
};

// main function, run after console reset
void main(void) {
  // set palette colors
  pal_all(PALETTE);

  // write text to name table
  put_str(NTADR_A(7,0), "Nametable A, Line 0");
  put_str(NTADR_A(7,1), "Nametable A, Line 1");
  put_str(NTADR_A(7,2), "Nametable A, Line 2");
  vram_adr(NTADR_A(0,3));
  vram_fill(5, 32);
  put_str(NTADR_A(2,4), "Nametable A, Line 4");
  put_str(NTADR_A(2,15),"Nametable A, Line 15");
  put_str(NTADR_A(2,27),"Nametable A, Line 27");
  put_str(NTADR_B(2,4), "Nametable B, Line 4");
  put_str(NTADR_B(2,15),"Nametable B, Line 15");
  put_str(NTADR_B(2,27),"Nametable B, Line 27");
  
  // set attributes
  vram_adr(0x23c0);
  vram_fill(0x55, 8);
  
  // set sprite 0
  oam_clear();
  oam_spr(1, 30, 0xa0, 1, 0);
  
  // clip left 8 pixels of screen
  ppu_mask(MASK_SPR|MASK_BG);
  
  // clear vram buffer
  vrambuf_clear();
  
  // enable PPU rendering (turn on screen)
  ppu_on_all();

  // scroll window back and forth
  scroll_demo();
}