uxn/src/devices/ppu.c

#include "ppu.h"

/*
Copyright (c) 2021 Devine Lu Linvega
Copyright (c) 2021 Andrew Alderwick

Permission to use, copy, modify, and distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE.
*/

/*
pixel 0001 0002
layer fgbg fgbg
byte  1010 1010
*/

static Uint8 blending[5][16] = {
	{0, 0, 0, 0, 1, 0, 1, 1, 2, 2, 0, 2, 3, 3, 3, 0},
	{0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3},
	{1, 2, 3, 1, 1, 2, 3, 1, 1, 2, 3, 1, 1, 2, 3, 1},
	{2, 3, 1, 2, 2, 3, 1, 2, 2, 3, 1, 2, 2, 3, 1, 2},
	{1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 0}};

static void
ppu_clear(Ppu *p)
{
	int row;
	for(row = 0; row < p->height * p->width / 2; ++row)
		p->pixels[row] = 0;
}

Uint8
ppu_read(Ppu *p, Uint16 x, Uint16 y)
{
	int row = (x + y * p->width) / 0x2;
	Uint8 seg = !(x & 0x1) << 2;
	Uint8 byte = p->pixels[row] >> seg;
	return (byte & 0x0c ? (byte >> 2) : byte) & 0x3;
}

void
ppu_write(Ppu *p, Uint8 layer, Uint16 x, Uint16 y, Uint8 color)
{
	int row = (x + y * p->width) / 0x2;
	Uint8 original = p->pixels[row];
	Uint8 next = 0x0;
	if(x % 2) {
		if(layer) {
			next |= original & 0xf3;
			next |= color << 0x02;
		} else {
			next |= original & 0xfc;
			next |= color;
		}
	} else {
		if(layer) {
			next |= original & 0x3f;
			next |= color << 0x06;
		} else {
			next |= original & 0xcf;
			next |= color << 0x04;
		}
	}
	p->pixels[row] = next;
	if(original != next)
		p->reqdraw = 1;
}

void
ppu_1bpp(Ppu *p, Uint8 layer, Uint16 x, Uint16 y, Uint8 *sprite, Uint8 color, Uint8 flipx, Uint8 flipy)
{
	Uint16 v, h;
	for(v = 0; v < 8; v++)
		for(h = 0; h < 8; h++) {
			Uint8 ch1 = (sprite[v] >> (7 - h)) & 0x1;
			if(ch1 || blending[4][color])
				ppu_write(p,
					layer,
					x + (flipx ? 7 - h : h),
					y + (flipy ? 7 - v : v),
					blending[ch1][color]);
		}
}

void
ppu_2bpp(Ppu *p, Uint8 layer, Uint16 x, Uint16 y, Uint8 *sprite, Uint8 color, Uint8 flipx, Uint8 flipy)
{
	Uint16 v, h;
	for(v = 0; v < 8; v++)
		for(h = 0; h < 8; h++) {
			Uint8 ch1 = ((sprite[v] >> (7 - h)) & 0x1);
			Uint8 ch2 = ((sprite[v + 8] >> (7 - h)) & 0x1);
			Uint8 ch = ch1 + ch2 * 2;
			if(ch || blending[4][color])
				ppu_write(p,
					layer,
					x + (flipx ? 7 - h : h),
					y + (flipy ? 7 - v : v),
					blending[ch][color]);
		}
}

/* output */

int
ppu_set_size(Ppu *p, Uint16 width, Uint16 height)
{
	ppu_clear(p);
	p->width = width;
	p->height = height;
	p->pixels = realloc(p->pixels, p->width * p->height * sizeof(Uint8) / 2);
	ppu_clear(p);
	return !!p->pixels;
}