nes: new horizscroll.c example

presets/nes/horizscroll.c

@@ -0,0 +1,227 @@
+
+/*
+We demonstrate horizontal scrolling of two nametables.
+Vertical mirroring is set, so nametables A and B are
+to the left and right of each other.
+
+New playfield data is randomly generated and updated
+offscreen using the vrambuf module.
+We update the nametable in 16-pixel-wide vertical strips,
+using 2x2 blocks of tiles ("metatiles").
+
+We also use the split() function to create a status bar.
+*/
+
+#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"
+
+/// GLOBAL VARIABLES
+
+word x_scroll;		// X scroll amount in pixels
+byte seg_height;	// segment height in metatiles
+byte seg_width;		// segment width in metatiles
+byte seg_char;		// character to draw
+byte seg_palette;	// attribute table value
+
+// number of rows in scrolling playfield (without status bar)
+#define PLAYROWS 24
+
+// buffers that hold vertical slices of nametable data
+char ntbuf1[PLAYROWS];	// left side
+char ntbuf2[PLAYROWS];	// right side
+
+// a vertical slice of attribute table entries
+char attrbuf[PLAYROWS/4];
+
+/// FUNCTIONS
+
+// convert from nametable address to attribute table address
+word nt2attraddr(word a) {
+  return (a & 0x2c00) | 0x3c0 |
+    ((a >> 4) & 0x38) | ((a >> 2) & 0x07);
+}
+
+// generate new random segment
+void new_segment() {
+  seg_height = (rand8() & 3) + 1;
+  seg_width = (rand8() & 3) + 1;
+  seg_palette = rand8() & 3;
+  seg_char = 0xf4;
+}
+
+// draw metatile into nametable buffers
+// y is the metatile coordinate (row * 2)
+// ch is the starting tile index in the pattern table
+void set_metatile(byte y, byte ch) {
+  ntbuf1[y*2] = ch;
+  ntbuf1[y*2+1] = ch+1;
+  ntbuf2[y*2] = ch+2;
+  ntbuf2[y*2+1] = ch+3;
+}
+
+// set attribute table entry in attrbuf
+// x and y are metatile coordinates
+// pal is the index to set
+void set_attr_entry(byte x, byte y, byte pal) {
+  if (y&1) pal <<= 4;
+  if (x&1) pal <<= 2;
+  attrbuf[y/2] |= pal;
+}
+
+// fill ntbuf with tile data
+// x = metatile coordinate
+void fill_buffer(byte x) {
+  byte i,y;
+  // clear nametable buffers
+  memset(ntbuf1, 0, sizeof(ntbuf1));
+  memset(ntbuf2, 0, sizeof(ntbuf2));
+  // draw a random star
+  ntbuf1[rand8() & 15] = '.';
+  // draw segment slice to both nametable buffers
+  for (i=0; i<seg_height; i++) {
+    y = PLAYROWS/2-1-i;
+    set_metatile(y, seg_char);
+    set_attr_entry(x, y, seg_palette);
+  }
+}
+
+// write attribute table buffer to vram buffer
+void put_attr_entries(word addr) {
+  byte i;
+  for (i=0; i<PLAYROWS/4; i++) {
+    VRAMBUF_PUT(addr, attrbuf[i], 0);
+    addr += 8;
+  }
+  vrambuf_end();
+}
+
+// update the nametable offscreen
+// called every 8 horizontal pixels
+void update_offscreen() {
+  register word addr;
+  byte x;
+  // divide x_scroll by 8
+  // to get nametable X position
+  x = (x_scroll/8 + 32) & 63;
+  // fill the ntbuf arrays with tiles
+  fill_buffer(x/2);
+  // get address in either nametable A or B
+  if (x < 32)
+    addr = NTADR_A(x, 4);
+  else
+    addr = NTADR_B(x&31, 4);
+  // draw vertical slice from ntbuf arrays to name table
+  // starting with leftmost slice
+  vrambuf_put(addr | VRAMBUF_VERT, ntbuf1, PLAYROWS);
+  // then the rightmost slice
+  vrambuf_put((addr+1) | VRAMBUF_VERT, ntbuf2, PLAYROWS);
+  // compute attribute table address
+  // then set attribute table entries
+  // we update these twice to prevent right-side artifacts
+  put_attr_entries(nt2attraddr(addr));
+  // every 4 columns, clear attribute table buffer
+  if ((x & 3) == 2) {
+    memset(attrbuf, 0, sizeof(attrbuf));
+  }
+  // decrement segment width, create new segment when it hits zero
+  if (--seg_width == 0) {
+    new_segment();
+  }
+}
+
+void scroll_left() {
+  // update nametable every 16 pixels
+  if ((x_scroll & 15) == 0) {
+    update_offscreen();
+  }
+  // increment x_scroll
+  ++x_scroll;
+}
+
+// function to scroll window up and down until end
+void scroll_demo() {
+  // get data for initial segment
+  new_segment();
+  x_scroll = 0;
+  // infinite loop
+  while (1) {
+    // ensure VRAM buffer is cleared
+    ppu_wait_nmi();
+    vrambuf_clear();
+    // split at x_scroll
+    split(x_scroll, 0);
+    // scroll to the left
+    scroll_left();
+  }
+}
+
+/*{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
+};
+
+// 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
+}
+
+// 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, 0, 0);
+  
+  // clear vram buffer
+  vrambuf_clear();
+  set_vram_update(updbuf);
+  
+  // enable PPU rendering (turn on screen)
+  ppu_on_all();
+
+  // scroll window back and forth
+  scroll_demo();
+}

src/platform/nes.ts

@@ -18,7 +18,7 @@ const JSNES_PRESETS = [
   {id:'metacursor.c', name:'Controllers'},
   {id:'vrambuffer.c', name:'VRAM Buffer'},
   {id:'statusbar.c', name:'Split Status Bar'},
-  {id:'horizmask.c', name:'Offscreen Scrolling'},
+  {id:'horizscroll.c', name:'Offscreen Scrolling'},
   {id:'siegegame.c', name:'Siege Game'},
   {id:'tint.c', name:'Color Emphasis'},
   {id:'rletitle.c', name:'Title Screen RLE'},