mirror of
https://github.com/sehugg/8bitworkshop.git
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169 lines
4.2 KiB
C
169 lines
4.2 KiB
C
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/*
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We demonstrate horizontal scrolling of two nametables.
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Vertical mirroring is set, so nametables A and B are
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to the left and right of each other.
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New playfield data is randomly generated and updated
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offscreen using the vrambuf module.
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Every 32 pixels, we also update the attribute table.
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We also use the split() function to create a status bar.
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*/
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#include "neslib.h"
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#include <string.h>
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// 0 = horizontal mirroring
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// 1 = vertical mirroring
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#define NES_MIRRORING 1
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// VRAM update buffer
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#include "vrambuf.h"
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//#link "vrambuf.c"
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// link the pattern table into CHR ROM
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//#link "chr_generic.s"
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// function to write a string into the name table
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// adr = start address in name table
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// str = pointer to string
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void put_str(unsigned int adr, const char *str) {
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vram_adr(adr); // set PPU read/write address
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vram_write(str, strlen(str)); // write bytes to PPU
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}
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word x_scroll; // X scroll amount in pixels
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byte bldg_height; // building height in tiles
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byte bldg_width; // building width in tiles
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byte bldg_char; // character to draw
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byte bldg_attr; // attribute table value
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#define PLAYROWS 24
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// convert from nametable address to attribute table address
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word nt2attraddr(word a) {
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return (a & 0x2c00) | 0x3c0 |
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((a >> 4) & 0x38) | ((a >> 2) & 0x07);
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}
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// generate new random building data
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void new_building() {
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bldg_height = (rand8() & 7) + 2;
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bldg_width = (rand8() & 3) * 4 + 4;
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bldg_char = (rand8() & 15);
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bldg_attr = rand8();
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}
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// update the nametable offscreen
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// called every 8 horizontal pixels
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void update_nametable() {
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register word addr;
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// a buffer drawn to the nametable vertically
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char buf[PLAYROWS];
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// divide x_scroll by 8
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// to get nametable X position
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byte x = (x_scroll/8 + 32) & 63;
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if (x < 32)
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addr = NTADR_A(x, 4);
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else
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addr = NTADR_B(x&31, 4);
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// clear empty space
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memset(buf, 0, sizeof(buf));
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// draw a random star
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buf[rand8() & 15] = '.';
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// draw roof
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buf[PLAYROWS-bldg_height-1] = bldg_char & 3;
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// draw rest of building
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memset(buf+PLAYROWS-bldg_height, bldg_char, bldg_height);
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// draw vertical slice in name table
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vrambuf_put(addr | VRAMBUF_VERT, buf, PLAYROWS);
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// every 4 columns, update attribute table
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if ((x & 3) == 1) {
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// compute attribute table address
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// of upper attribute block
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addr = nt2attraddr(addr) + 8*4;
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VRAMBUF_PUT(addr, bldg_attr, 0);
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// put lower attribute block
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addr += 8;
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VRAMBUF_PUT(addr, bldg_attr, 0);
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vrambuf_end();
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}
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// generate new building?
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if (--bldg_width == 0) {
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new_building();
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}
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}
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// function to scroll window up and down until end
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void scroll_demo() {
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// make 1st building
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new_building();
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x_scroll = 0;
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// infinite loop
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while (1) {
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// update nametable every 8 pixels
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if ((x_scroll & 7) == 0) {
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update_nametable();
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}
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// ensure VRAM buffer is cleared
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ppu_wait_nmi();
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vrambuf_clear();
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// split at x_scroll
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split(x_scroll, 0);
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// increment x_scroll
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++x_scroll;
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}
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}
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/*{pal:"nes",layout:"nes"}*/
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const char PALETTE[32] = {
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0x03, // background color
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0x25,0x30,0x27,0x00, // ladders and pickups
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0x1C,0x20,0x2C,0x00, // floor blocks
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0x00,0x10,0x20,0x00,
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0x06,0x16,0x26,0x00,
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0x16,0x35,0x24,0x00, // enemy sprites
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0x00,0x37,0x25,0x00, // rescue person
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0x0D,0x2D,0x1A,0x00,
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0x0D,0x27,0x2A // player sprites
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};
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// main function, run after console reset
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void main(void) {
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// set palette colors
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pal_all(PALETTE);
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// write text to name table
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put_str(NTADR_A(7,0), "Nametable A, Line 0");
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put_str(NTADR_A(7,1), "Nametable A, Line 1");
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put_str(NTADR_A(7,2), "Nametable A, Line 2");
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vram_adr(NTADR_A(0,3));
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vram_fill(5, 32);
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put_str(NTADR_A(2,4), "Nametable A, Line 4");
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put_str(NTADR_A(2,15),"Nametable A, Line 15");
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put_str(NTADR_A(2,27),"Nametable A, Line 27");
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put_str(NTADR_B(2,4), "Nametable B, Line 4");
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put_str(NTADR_B(2,15),"Nametable B, Line 15");
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put_str(NTADR_B(2,27),"Nametable B, Line 27");
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// set attributes
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vram_adr(0x23c0);
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vram_fill(0x55, 8);
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// set sprite 0
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oam_clear();
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oam_spr(1, 30, 0xa0, 0, 0);
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// clear vram buffer
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vrambuf_clear();
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set_vram_update(updbuf);
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// enable PPU rendering (turn on screen)
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ppu_on_all();
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// scroll window back and forth
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scroll_demo();
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}
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