From 4405fa6bbf6190f22c55a7fc98d051923902e98c Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Fri, 21 Oct 2022 05:12:21 -0300
Subject: [PATCH] feat: implement hofs and vofs on io bus

---
 src/bus/io.zig | 18 ++++++++++++++++--
 src/ppu.zig    |  4 +---
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/src/bus/io.zig b/src/bus/io.zig
index 07ed7cc..4bef89c 100644
--- a/src/bus/io.zig
+++ b/src/bus/io.zig
@@ -142,6 +142,14 @@ pub fn read32(bus: *const Bus, addr: u32) u32 {
 pub fn write32(bus: *Bus, addr: u32, word: u32) void {
     switch (addr) {
         0x0400_0000 => bus.ppu.dispcnt.raw = @truncate(u16, word),
+        0x0400_0010 => bus.ppu.bg[0].hofs.raw = @truncate(u16, word), // TODO: Don't write out every HOFS / VOFS?
+        0x0400_0012 => bus.ppu.bg[0].vofs.raw = @truncate(u16, word),
+        0x0400_0014 => bus.ppu.bg[1].hofs.raw = @truncate(u16, word),
+        0x0400_0016 => bus.ppu.bg[1].vofs.raw = @truncate(u16, word),
+        0x0400_0018 => bus.ppu.bg[2].hofs.raw = @truncate(u16, word),
+        0x0400_001A => bus.ppu.bg[2].vofs.raw = @truncate(u16, word),
+        0x0400_001C => bus.ppu.bg[3].hofs.raw = @truncate(u16, word),
+        0x0400_001E => bus.ppu.bg[3].vofs.raw = @truncate(u16, word),
         0x0400_0200 => bus.io.ie.raw = @truncate(u16, word),
         0x0400_0208 => bus.io.ime = word & 1 == 1,
         else => std.debug.panic("[I/O:32] tried to write 0x{X:} to 0x{X:}", .{ word, addr }),
@@ -164,9 +172,15 @@ 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.bg[0].cnt.raw = halfword,
-        0x0400_0010 => bus.ppu.bg[0].hofs.raw = halfword,
+        0x0400_0008...0x0400_000F => bus.ppu.bg[addr & 0x7].cnt.raw = halfword,
+        0x0400_0010 => bus.ppu.bg[0].hofs.raw = halfword, // TODO: Don't write out every HOFS / VOFS?
         0x0400_0012 => bus.ppu.bg[0].vofs.raw = halfword,
+        0x0400_0014 => bus.ppu.bg[1].hofs.raw = halfword,
+        0x0400_0016 => bus.ppu.bg[1].vofs.raw = halfword,
+        0x0400_0018 => bus.ppu.bg[2].hofs.raw = halfword,
+        0x0400_001A => bus.ppu.bg[2].vofs.raw = halfword,
+        0x0400_001C => bus.ppu.bg[3].hofs.raw = halfword,
+        0x0400_001E => bus.ppu.bg[3].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,
diff --git a/src/ppu.zig b/src/ppu.zig
index fea7077..f5c8e54 100644
--- a/src/ppu.zig
+++ b/src/ppu.zig
@@ -61,8 +61,6 @@ pub const Ppu = struct {
     }
 
     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);
@@ -97,7 +95,7 @@ pub const Ppu = struct {
 
             // 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]));
+            const entry = @bitCast(ScreenEntry, @as(u16, self.vram.get16(entry_addr)));
 
             // Calculate the Address of the Tile in the designated Charblock
             // We also take this opportunity to flip tiles if necessary