From ec25a9aae4928d03ae8ec75b115cced1cba78596 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Sun, 13 Feb 2022 04:04:10 -0400
Subject: [PATCH] feat: implement BG Scrolling Registers

---
 src/bus/io.zig | 33 +++++++++++++++++++++++++++++++++
 src/ppu.zig    |  6 +++++-
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/src/bus/io.zig b/src/bus/io.zig
index 66561ec..134fedb 100644
--- a/src/bus/io.zig
+++ b/src/bus/io.zig
@@ -17,6 +17,24 @@ pub const Io = struct {
     bg2cnt: BackgroundControl,
     /// Read / Write
     bg3cnt: BackgroundControl,
+
+    /// Write Only
+    bg0hofs: BackgroundOffset,
+    /// Write Only
+    bg0vofs: BackgroundOffset,
+    /// Write Only
+    bg1hofs: BackgroundOffset,
+    /// Write Only
+    bg1vofs: BackgroundOffset,
+    /// Write Only
+    bg2hofs: BackgroundOffset,
+    /// Write Only
+    bg2vofs: BackgroundOffset,
+    /// Write Only
+    bg3hofs: BackgroundOffset,
+    /// Write Only
+    bg3vofs: BackgroundOffset,
+
     /// Read / Write
     ime: bool,
     ie: InterruptEnable,
@@ -34,6 +52,14 @@ pub const Io = struct {
             .bg1cnt = .{ .raw = 0x0000 },
             .bg2cnt = .{ .raw = 0x0000 },
             .bg3cnt = .{ .raw = 0x0000 },
+            .bg0hofs = .{ .raw = 0x0000 },
+            .bg0vofs = .{ .raw = 0x0000 },
+            .bg1hofs = .{ .raw = 0x0000 },
+            .bg1vofs = .{ .raw = 0x0000 },
+            .bg2hofs = .{ .raw = 0x0000 },
+            .bg2vofs = .{ .raw = 0x0000 },
+            .bg3hofs = .{ .raw = 0x0000 },
+            .bg3vofs = .{ .raw = 0x0000 },
             .ime = false,
             .ie = .{ .raw = 0x0000 },
             .irq = .{ .raw = 0x0000 },
@@ -78,6 +104,8 @@ pub const Io = struct {
             0x0400_0000 => self.dispcnt.raw = halfword,
             0x0400_0004 => self.dispstat.raw = halfword,
             0x0400_0008 => self.bg0cnt.raw = halfword,
+            0x0400_0010 => self.bg0hofs.raw = halfword,
+            0x0400_0012 => self.bg0vofs.raw = halfword,
             0x0400_0200 => self.ie.raw = halfword,
             0x0400_0202 => self.irq.raw = halfword,
             0x0400_0208 => self.ime = halfword & 1 == 1,
@@ -181,6 +209,11 @@ const BackgroundControl = extern union {
     raw: u16,
 };
 
+const BackgroundOffset = extern union {
+    offset: Bitfield(u16, 0, 9),
+    raw: u16,
+};
+
 const InterruptRequest = extern union {
     vblank: Bit(u16, 0),
     hblank: Bit(u16, 1),
diff --git a/src/ppu.zig b/src/ppu.zig
index c89d00f..dbc555e 100644
--- a/src/ppu.zig
+++ b/src/ppu.zig
@@ -47,6 +47,10 @@ pub const Ppu = struct {
         const scanline = io.vcount.scanline.read();
 
         switch (bg_mode) {
+            0x0 => {
+                // Mode 0
+
+            },
             0x3 => {
                 const start = framebuf_pitch * @as(usize, scanline);
                 const end = start + framebuf_pitch;
@@ -70,7 +74,7 @@ pub const Ppu = struct {
                     self.framebuf[buf_start + j] = self.palette.buf[id];
                 }
             },
-            else => {}, // std.debug.panic("[PPU] TODO: Implement BG Mode {}", .{bg_mode}),
+            else => std.debug.panic("[PPU] TODO: Implement BG Mode {}", .{bg_mode}),
         }
     }
 };