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feat(ppu): implement bg priority and transparency

This commit is contained in:
Rekai Nyangadzayi Musuka 2022-03-02 00:59:33 -04:00
parent 90302d1c52
commit 3d8c944bcc
1 changed files with 38 additions and 21 deletions
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59
src/ppu.zig
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@ -31,6 +31,8 @@ pub const Ppu = struct {
framebuf: []u8,
alloc: Allocator,
scanline_buf: [width]?u16,
pub fn init(alloc: Allocator, sched: *Scheduler) !Self {
// Queue first Hblank
sched.push(.Draw, sched.tick + (240 * 4));
@ -51,6 +53,8 @@ pub const Ppu = struct {
.dispcnt = .{ .raw = 0x0000 },
.dispstat = .{ .raw = 0x0000 },
.vcount = .{ .raw = 0x0000 },
.scanline_buf = [_]?u16{null} ** width,
};
}
@ -60,12 +64,7 @@ pub const Ppu = struct {
self.palette.deinit();
}
fn drawBackround(self: *Self, comptime n: u3, scanline: u32) void {
// 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);
fn drawBackround(self: *Self, comptime n: u3) void {
// 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;
@ -87,10 +86,13 @@ pub const Ppu = struct {
const vofs = self.bg[n].vofs.offset.read();
const hofs = self.bg[n].hofs.offset.read();
const y = vofs + scanline;
const y = vofs + self.vcount.scanline.read();
var i: u32 = 0;
while (i < width) : (i += 1) {
// Exit early if a pixel is already here
if (self.scanline_buf[i] != null) continue;
const x = hofs + i;
// Grab the Screen Entry from VRAM
@ -107,25 +109,21 @@ pub const Ppu = struct {
// 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];
const 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 pal_id = if (!is_8bpp) blk: {
tile = if (col & 1 == 1) tile >> 4 else tile & 0xF;
const pal_bank: u16 = @as(u8, entry.palette_bank.read()) << 4;
const nybble_tile = if (col & 1 == 1) tile >> 4 else tile & 0xF;
if (nybble_tile == 0) break :blk 0;
// If Tile is 0 then we need to access the Backdrop
// The backdrop is the first colour in Palette RAM
// AFAIK there is no special logic needed for doing this in 8bpp
break :blk if (tile == 0) 0 else pal_bank | tile;
const pal_bank: u16 = @as(u8, entry.palette_bank.read()) << 4;
break :blk pal_bank | nybble_tile;
} else tile;
std.mem.copy(u8, scanline_buf[i * 2 ..][0..2], self.palette.buf[pal_id * 2 ..][0..2]);
if (pal_id != 0) self.scanline_buf[i] = self.palette.get16(pal_id * 2);
}
std.mem.copy(u8, self.framebuf[start..][0..framebuf_pitch], &scanline_buf);
}
pub fn drawScanline(self: *Self) void {
@ -135,13 +133,28 @@ pub const Ppu = struct {
switch (bg_mode) {
0x0 => {
const start = framebuf_pitch * @as(usize, scanline);
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);
// Draw Sprites Here
if (i == self.bg[0].cnt.priority.read() and bg_enable & 1 == 1) self.drawBackround(0);
if (i == self.bg[1].cnt.priority.read() and bg_enable >> 1 & 1 == 1) self.drawBackround(1);
if (i == self.bg[2].cnt.priority.read() and bg_enable >> 2 & 1 == 1) self.drawBackround(2);
if (i == self.bg[3].cnt.priority.read() and bg_enable >> 3 & 1 == 1) self.drawBackround(3);
}
// Copy Drawn Scanline to Frame Buffer
// If there are any nulls present in self.scanline_buf it means that no background drew a pixel there, so draw backdrop
for (self.scanline_buf) |maybe_px, j| {
const bgr555 = if (maybe_px) |px| px else self.palette.getBackdrop();
self.framebuf[(start + j * 2 + 1)] = @truncate(u8, bgr555 >> 8);
self.framebuf[(start + j * 2 + 0)] = @truncate(u8, bgr555);
}
// Reset Scanline Buffer
std.mem.set(?u16, &self.scanline_buf, null);
},
0x3 => {
const start = framebuf_pitch * @as(usize, scanline);
@ -237,6 +250,10 @@ const Palette = struct {
pub fn get8(self: *const Self, idx: usize) u8 {
return self.buf[idx];
}
fn getBackdrop(self: *const Self) u16 {
return self.get16(0);
}
};
const Vram = struct {