mirror of
https://github.com/sehugg/8bitworkshop.git
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168 lines
3.5 KiB
C
168 lines
3.5 KiB
C
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/*
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Creates a monochrome frame buffer in video RAM.
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We map the pattern tables to CHR RAM, using the UxROM (2) mapper.
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By cleverly setting up palettes, and using a split-screen
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CHR bank switch, we split the screen into four different regions
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that display their own pixels.
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*/
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#include "neslib.h"
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#include "nes.h"
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#include <stdlib.h>
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#define NES_MAPPER 2 // UxROM mapper
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#define NES_CHR_BANKS 0 // CHR RAM
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bool ppu_is_on = false;
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#define DELAYLOOP(n) \
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__asm__("ldy #%b", n); \
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__asm__("@1: dey"); \
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__asm__("bne @1");
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void monobitmap_split() {
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// split screen at line 128
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split(0,0);
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DELAYLOOP(15); // delay until end of line
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PPU.control = PPU.control ^ 0x10; // bg bank 1
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}
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void monobitmap_set_pixel(byte x, byte y, byte color) {
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byte b;
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// compute pattern table address
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word a = (x/8)*16 | ((y&63)/8)*(16*32) | (y&7);
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if (y & 64) a |= 8;
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if (y & 128) a |= 0x1000;
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// if PPU is active, wait for next frame
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if (ppu_is_on) {
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ppu_wait_nmi();
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}
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// read old byte
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vram_adr(a);
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vram_read(&b, 1);
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if (color) {
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b |= 128 >> (x&7); // set pixel
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} else {
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b &= ~(128 >> (x&7)); // clear pixel
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}
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// write new byte
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vram_adr(a);
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vram_put(b);
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// if PPU is active, reset PPU addr and split screen
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if (ppu_is_on) {
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vram_adr(0);
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monobitmap_split();
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}
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}
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void monobitmap_draw_line(int x0, int y0, int x1, int y1, byte color) {
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int dx = abs(x1-x0);
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int sx = x0<x1 ? 1 : -1;
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int dy = abs(y1-y0);
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int sy = y0<y1 ? 1 : -1;
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int err = (dx>dy ? dx : -dy)>>1;
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int e2;
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for(;;) {
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monobitmap_set_pixel(x0, y0, color);
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if (x0==x1 && y0==y1) break;
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e2 = err;
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if (e2 > -dx) { err -= dy; x0 += sx; }
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if (e2 < dy) { err += dx; y0 += sy; }
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}
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}
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// write values 0..255
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void monobitmap_put_256inc() {
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word i;
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for (i=0; i<256; i++)
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vram_put(i);
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}
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void monobitmap_put_attrib() {
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vram_fill(0x00, 0x10); // first palette
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vram_fill(0x55, 0x10); // second palette
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}
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void monobitmap_clear() {
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// clear pattern table
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vram_adr(0x0);
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vram_fill(0x0, 0x2000);
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}
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void monobitmap_setup() {
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monobitmap_clear();
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// setup nametable A and B
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vram_adr(NAMETABLE_A);
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monobitmap_put_256inc();
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monobitmap_put_256inc();
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monobitmap_put_256inc();
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monobitmap_put_256inc();
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vram_adr(NAMETABLE_A + 0x3c0);
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monobitmap_put_attrib();
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monobitmap_put_attrib();
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bank_bg(0);
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// setup sprite 0
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bank_spr(1);
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oam_clear();
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oam_size(0);
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oam_spr(247, 125, 255, 0, 0);
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// draw a pixel for it to collide with
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monobitmap_set_pixel(247, 126, 1);
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// make sprite 255 = white line
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vram_adr(0x1ff0);
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vram_fill(0xff, 0x1);
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}
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/*{pal:"nes",layout:"nes"}*/
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const byte MONOBMP_PALETTE[16] = {
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0x03,
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0x30, 0x03, 0x30, 0x00,
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0x03, 0x30, 0x30, 0x00,
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0x30, 0x03, 0x30, 0x00,
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0x03, 0x30, 0x30
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};
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void monobitmap_demo() {
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byte i;
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static const byte x1 = 16;
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static const byte y1 = 16;
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static const byte x2 = 240;
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static const byte y2 = 208;
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for (i=x1; i<=x2; i++) {
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monobitmap_set_pixel(i,y1,1);
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monobitmap_set_pixel(i,y2,1);
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}
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for (i=y1; i<=y2; i++) {
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monobitmap_set_pixel(x1,i,1);
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monobitmap_set_pixel(x2,i,1);
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}
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for (i=x1; i<x2; i+=16) {
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monobitmap_draw_line(x1,y1,i,y2,1);
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}
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for (i=y1; i<=y2; i+=16) {
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monobitmap_draw_line(x1,y1,x2,i,1);
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}
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}
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void main(void)
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{
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monobitmap_setup();
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pal_bg(MONOBMP_PALETTE);
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monobitmap_demo();
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ppu_on_all();
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while (!pad_trigger(0)) {
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ppu_wait_nmi();
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monobitmap_split();
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}
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ppu_off();
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monobitmap_setup();
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ppu_on_all();
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ppu_is_on = true;
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monobitmap_demo();
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while(1) {
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ppu_wait_nmi();
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monobitmap_split();
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}
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}
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