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feat: add support for multiple BGs in Mode 0

This commit is contained in:
Rekai Nyangadzayi Musuka 2022-02-16 03:27:06 -04:00
parent d2d4667f7b
commit ce97a52868
2 changed files with 74 additions and 69 deletions
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6
src/bus/io.zig
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@ -164,9 +164,9 @@ pub fn write16(bus: *Bus, addr: u32, halfword: u16) void {
switch (addr) {
0x0400_0000 => bus.ppu.dispcnt.raw = halfword,
0x0400_0004 => bus.ppu.dispstat.raw = halfword,
0x0400_0008 => bus.ppu.bg0.cnt.raw = halfword,
0x0400_0010 => bus.ppu.bg0.hofs.raw = halfword,
0x0400_0012 => bus.ppu.bg0.vofs.raw = halfword,
0x0400_0008 => bus.ppu.bg[0].cnt.raw = halfword,
0x0400_0010 => bus.ppu.bg[0].hofs.raw = halfword,
0x0400_0012 => bus.ppu.bg[0].vofs.raw = halfword,
0x0400_0200 => bus.io.ie.raw = halfword,
0x0400_0202 => bus.io.irq.raw = halfword,
0x0400_0208 => bus.io.ime = halfword & 1 == 1,

137
src/ppu.zig
View File

@ -17,10 +17,8 @@ pub const Ppu = struct {
const Self = @This();
// Registers
bg0: Background,
bg1: Background,
bg2: Background,
bg3: Background,
bg: [4]Background,
dispcnt: io.DisplayControl,
dispstat: io.DisplayStatus,
@ -49,10 +47,7 @@ pub const Ppu = struct {
.alloc = alloc,
// Registers
.bg0 = Background.init(),
.bg1 = Background.init(),
.bg2 = Background.init(),
.bg3 = Background.init(),
.bg = [_]Background{Background.init()} ** 4,
.dispcnt = .{ .raw = 0x0000 },
.dispstat = .{ .raw = 0x0000 },
.vcount = .{ .raw = 0x0000 },
@ -65,71 +60,81 @@ pub const Ppu = struct {
self.palette.deinit();
}
fn drawBackround(self: *Self, comptime n: u3, scanline: u32) void {
// TODO: Consider Scrolling
// The Current Scanline which will be copied into
// the Framebuffer
const start = framebuf_pitch * @as(usize, scanline);
var scanline_buf = std.mem.zeroes([framebuf_pitch]u8);
// A Tile in a charblock is a byte, while a Screen Entry is a halfword
const charblock_len: u32 = 0x4000;
const screenblock_len: u32 = 0x800;
const cbb: u2 = self.bg[n].cnt.char_base.read(); // Char Block Base
const sbb: u5 = self.bg[n].cnt.screen_base.read(); // Screen Block Base
const is_8bpp: bool = self.bg[n].cnt.colour_mode.read(); // Colour Mode
const size: u2 = self.bg[n].cnt.size.read(); // Background Size
// In 4bpp: 1 byte represents two pixels so the length is (8 x 8) / 2
// In 8bpp: 1 byte represents one pixel so the length is 8 x 8
const tile_len = if (is_8bpp) @as(u32, 0x40) else 0x20;
const tile_row_offset = if (is_8bpp) @as(u32, 0x8) else 0x4;
// 0x0600_000 is implied because we can access VRAM without the Bus
const char_base: u32 = charblock_len * @as(u32, cbb);
const screen_base: u32 = screenblock_len * @as(u32, sbb);
const y = scanline;
var x: u32 = 0;
while (x < width) : (x += 1) {
// Grab the Screen Entry from VRAM
const entry_addr = screen_base + tilemapOffset(size, x, y);
const entry = @bitCast(ScreenEntry, @as(u16, self.vram.buf[entry_addr + 1]) << 8 | @as(u16, self.vram.buf[entry_addr]));
// Calculate the Address of the Tile in the designated Charblock
// We also take this opportunity to flip tiles if necessary
const tile_id: u32 = entry.tile_id.read();
const row = if (entry.h_flip.read()) 7 - (y % 8) else y % 8; // Determine on which row in a tile we're on
const tile_addr = char_base + (tile_len * tile_id) + (tile_row_offset * row);
// Calculate on which column in a tile we're on
// Similarly to when we calculated the row, if we're in 4bpp we want to account
// for 1 byte consisting of two pixels
const col = if (entry.v_flip.read()) 7 - (x % 8) else x % 8;
var tile = self.vram.buf[tile_addr + if (is_8bpp) col else col / 2];
// If we're in 8bpp, then the tile value is an index into the palette,
// If we're in 4bpp, we have to account for a pal bank value in the Screen entry
// and then we can index the palette
const colour = if (!is_8bpp) blk: {
tile = if (col & 1 == 1) tile >> 4 else tile & 0xF;
const pal_bank: u8 = @as(u8, entry.palette_bank.read()) << 4;
break :blk pal_bank | tile;
} else tile;
std.mem.copy(u8, scanline_buf[x * 2 ..][0..2], self.palette.buf[colour * 2 ..][0..2]);
}
std.mem.copy(u8, self.framebuf[start..][0..framebuf_pitch], &scanline_buf);
}
pub fn drawScanline(self: *Self) void {
const bg_mode = self.dispcnt.bg_mode.read();
const bg_enable = self.dispcnt.bg_enable.read();
const scanline = self.vcount.scanline.read();
switch (bg_mode) {
0x0 => {
// TODO: Consider more than BG0
// TODO: Consider Scrolling
// The Current Scanline which will be copied into
// the Framebuffer
const start = framebuf_pitch * @as(usize, scanline);
var scanline_buf = std.mem.zeroes([framebuf_pitch]u8);
// A Tile in a charblock is a byte, while a Screen Entry is a halfword
const charblock_len: u32 = 0x4000;
const screenblock_len: u32 = 0x800;
const cbb: u2 = self.bg0.cnt.char_base.read(); // Char Block Base
const sbb: u5 = self.bg0.cnt.screen_base.read(); // Screen Block Base
const is_8bpp: bool = self.bg0.cnt.colour_mode.read(); // Colour Mode
const size: u2 = self.bg0.cnt.size.read(); // Background Size
// In 4bpp: 1 byte represents two pixels so the length is (8 x 8) / 2
// In 8bpp: 1 byte represents one pixel so the length is 8 x 8
const tile_len = if (is_8bpp) @as(u32, 0x40) else 0x20;
const tile_row_offset = if (is_8bpp) @as(u32, 0x8) else 0x4;
// 0x0600_000 is implied because we can access VRAM without the Bus
const char_base: u32 = charblock_len * @as(u32, cbb);
const screen_base: u32 = screenblock_len * @as(u32, sbb);
const y = @as(u32, scanline);
var x: u32 = 0;
while (x < width) : (x += 1) {
// Grab the Screen Entry from VRAM
const entry_addr = screen_base + tilemapOffset(size, x, y);
const entry = @bitCast(ScreenEntry, @as(u16, self.vram.buf[entry_addr + 1]) << 8 | @as(u16, self.vram.buf[entry_addr]));
// Calculate the Address of the Tile in the designated Charblock
// We also take this opportunity to flip tiles if necessary
const tile_id: u32 = entry.tile_id.read();
const row = if (entry.h_flip.read()) 7 - (y % 8) else y % 8; // Determine on which row in a tile we're on
const tile_addr = char_base + (tile_len * tile_id) + (tile_row_offset * row);
// Calculate on which column in a tile we're on
// Similarly to when we calculated the row, if we're in 4bpp we want to account
// for 1 byte consisting of two pixels
const col = if (entry.v_flip.read()) 7 - (x % 8) else x % 8;
var tile = self.vram.buf[tile_addr + if (is_8bpp) col else col / 2];
// If we're in 8bpp, then the tile value is an index into the palette,
// If we're in 4bpp, we have to account for a pal bank value in the Screen entry
// and then we can index the palette
const colour = if (!is_8bpp) blk: {
tile = if (col & 1 == 1) tile >> 4 else tile & 0xF;
const pal_bank: u8 = @as(u8, entry.palette_bank.read()) << 4;
break :blk pal_bank | tile;
} else tile;
std.mem.copy(u8, scanline_buf[x * 2 ..][0..2], self.palette.buf[colour * 2 ..][0..2]);
var i: usize = 0;
while (i < 4) : (i += 1) {
if (i == self.bg[0].cnt.priority.read() and bg_enable & 1 == 1) self.drawBackround(0, scanline);
if (i == self.bg[1].cnt.priority.read() and bg_enable >> 1 & 1 == 1) self.drawBackround(1, scanline);
if (i == self.bg[2].cnt.priority.read() and bg_enable >> 2 & 1 == 1) self.drawBackround(2, scanline);
if (i == self.bg[3].cnt.priority.read() and bg_enable >> 3 & 1 == 1) self.drawBackround(3, scanline);
}
std.mem.copy(u8, self.framebuf[start..][0..framebuf_pitch], &scanline_buf);
},
0x3 => {
const start = framebuf_pitch * @as(usize, scanline);