chore: prevent bitrot

closes #1

.vscode/extensions.json

@@ -1,6 +1,6 @@
 {
     "recommendations": [
-        "matklad.rust-analyzer",
+        "rust-lang.rust-analyzer",
         "tamasfe.even-better-toml",
         "serayuzgur.crates",
         "vadimcn.vscode-lldb",

Cargo.toml

@@ -8,21 +8,21 @@ edition = "2021"
 
 [dependencies]
 anyhow = "1.0"
-bitfield = "0.13"
-clap = "2.33"
-gilrs = "0.8"
-winit = "0.26"
-egui = "0.15"
-wgpu = "0.11"
-egui_wgpu_backend = "0.14"
-egui_winit_platform = "0.12"
-pollster = "0.2"
-rodio = "0.14"
-rtrb = "0.2"
+bitfield = "0.17"
+clap = { version = "4.0", features = ["cargo"] }
+gilrs = "0.11"
+winit = "0.28"
+egui = "0.21"
+egui_wgpu_backend = "0.22"
+egui_winit_platform = "0.18"
+pollster = "0.3"
+rodio = "0.19"
+rtrb = "0.3"
 directories-next = "2.0"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["std", "env-filter"] }
 thiserror = "1.0"
+once_cell = "1.10"
 
 [profile.release]
 debug = true

README.md

@@ -1,10 +1,9 @@
 # Rekai's Gameboy Emulator
-[![Build Status](https://ci.paoda.moe/api/badges/paoda/gb/status.svg)](https://ci.paoda.moe/paoda/gb)
 
 ### Status
 * From [Blargg Test ROMs](https://github.com/L-P/blargg-test-roms/)
     * [x] cpu_instrs
-    * [ ] instr_timing (kind of)
+    * [x] instr_timing
     * [x] mem_timing
     * [x] mem_timing-2
     * [ ] dmg_sound (partial) 
@@ -21,9 +20,15 @@
 Supports: ROM-only, MBC1, MBC2, MBC3 and MBC5 games.
 
 
+### Compiling
+This project was last successfully built on [Rust 1.64.0](https://github.com/rust-lang/rust/tree/1.64.0)
+
+1. `git clone https://github.com/paoda/gb`
+2. `cd gb`
+3. `cargo run --release`
 
 ### Controls
-Controls are defined [here](https://git.musuka.dev/paoda/gb/src/branch/main/src/joypad.rs#L114)
+Controls are defined [here](https://github.com/paoda/gb/blob/85940c874460b9cb31bf9b8211bf7dda596d114a/src/joypad.rs#L114)
 
 Key | Button
 --- | ---

src/apu/types.rs

@@ -169,7 +169,7 @@ pub(super) mod ch4 {
             match byte & 0x01 {
                 0b00 => Self::Short,
                 0b01 => Self::Long,
-                _ => unreachable!("{:#04X} is not a valid value for CounterWidth"),
+                _ => unreachable!("{:#04X} is not a valid value for CounterWidth", byte),
             }
         }
     }

src/cartridge.rs

@@ -61,8 +61,9 @@ impl Cartridge {
             MbcKind::Mbc2(hw) => Box::new(Mbc2::new(hw, rom_cap)),
             MbcKind::Mbc3(hw @ Mbc3Hardware::Rtc) => Box::new(Mbc3::new(hw, ram_cap)),
             MbcKind::Mbc3(hw @ Mbc3Hardware::RtcBatteryRam) => Box::new(Mbc3::new(hw, ram_cap)),
-            MbcKind::Mbc4(hw @ Mbc5Hardware::None) => Box::new(Mbc5::new(hw, ram_cap, rom_cap)),
-            MbcKind::Mbc4(hw @ Mbc5Hardware::BatteryRam) => {
+            MbcKind::Mbc3(hw @ Mbc3Hardware::BatteryRam) => Box::new(Mbc3::new(hw, ram_cap)),
+            MbcKind::Mbc5(hw @ Mbc5Hardware::None) => Box::new(Mbc5::new(hw, ram_cap, rom_cap)),
+            MbcKind::Mbc5(hw @ Mbc5Hardware::BatteryRam) => {
                 Box::new(Mbc5::new(hw, ram_cap, rom_cap))
             }
             kind => todo!("ROMS with {:?} are currently unsupported", kind),
@@ -70,21 +71,23 @@ impl Cartridge {
     }
 
     fn detect_title(title_mem: &[u8; ROM_TITLE_MAX_SIZE]) -> Option<String> {
+        use std::str::from_utf8;
+
         const ALT_TITLE_LEN: usize = ROM_MANUFACTURER_START - ROM_TITLE_START;
 
-        // byte slice we have here is purposely not null terminated
+        // ascii byte slie does not have a null-terminator
         let ascii = match title_mem.iter().position(|b| *b == 0x00) {
-            Some(end) => &title_mem[0..end],
-            None => &title_mem[0..ROM_TITLE_MAX_SIZE],
+            Some(end) => &title_mem[..end],
+            None => &title_mem[..ROM_TITLE_MAX_SIZE],
         };
 
-        match std::str::from_utf8(ascii).ok() {
-            None => match std::str::from_utf8(&title_mem[0..ALT_TITLE_LEN]).ok() {
+        match from_utf8(ascii).map(str::trim).ok() {
+            None => match from_utf8(&title_mem[..ALT_TITLE_LEN]).map(str::trim).ok() {
                 Some("") | None => None,
-                Some(title) => Some(String::from(title.trim())),
+                Some(title) => Some(String::from(title)),
             },
             Some("") => None,
-            Some(title) => Some(String::from(title.trim())),
+            Some(title) => Some(String::from(title)),
         }
     }
 
@@ -105,12 +108,12 @@ impl Cartridge {
             0x11 => Mbc3(Mbc3Hardware::None),
             0x12 => Mbc3(Mbc3Hardware::Ram),
             0x13 => Mbc3(Mbc3Hardware::BatteryRam),
-            0x19 => Mbc4(Mbc5Hardware::None),
-            0x1A => Mbc4(Mbc5Hardware::Ram),
-            0x1B => Mbc4(Mbc5Hardware::BatteryRam),
-            0x1C => Mbc4(Mbc5Hardware::Rumble),
-            0x1D => Mbc4(Mbc5Hardware::RumbleRam),
-            0x1E => Mbc4(Mbc5Hardware::RumbleBatteryRam),
+            0x19 => Mbc5(Mbc5Hardware::None),
+            0x1A => Mbc5(Mbc5Hardware::Ram),
+            0x1B => Mbc5(Mbc5Hardware::BatteryRam),
+            0x1C => Mbc5(Mbc5Hardware::Rumble),
+            0x1D => Mbc5(Mbc5Hardware::RumbleRam),
+            0x1E => Mbc5(Mbc5Hardware::RumbleBatteryRam),
             id => unimplemented!("MBC with code {:#04X} is unsupported", id),
         }
     }
@@ -746,7 +749,7 @@ enum MbcKind {
     Mbc1(Mbc1Hardware),
     Mbc2(Mbc2Hardware),
     Mbc3(Mbc3Hardware),
-    Mbc4(Mbc5Hardware),
+    Mbc5(Mbc5Hardware),
 }
 
 #[derive(Debug, Clone, Copy)]
@@ -950,4 +953,14 @@ mod tests {
             Cartridge::detect_title(&title)
         );
     }
+
+    #[test]
+    fn all_whitespace_title() {
+        let title = [
+            0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+            0x00, 0x00,
+        ];
+
+        assert_eq!(None, Cartridge::detect_title(&title));
+    }
 }

src/emu.rs

@@ -44,7 +44,8 @@ pub fn save_and_exit(cpu: &Cpu, control_flow: &mut ControlFlow) {
 
 #[inline]
 pub fn pixel_buf(cpu: &Cpu) -> &[u8; GB_HEIGHT * GB_WIDTH * 4] {
-    cpu.bus.ppu.frame_buf.as_ref()
+    use crate::ppu::Device;
+    cpu.bus.ppu.frame_buf.get(Device::Host)
 }
 
 pub fn from_boot_rom<P: AsRef<Path>>(path: P) -> std::io::Result<Cpu> {
@@ -64,8 +65,7 @@ pub fn rom_title(cpu: &Cpu) -> &str {
     cpu.bus
         .cart
         .as_ref()
-        .map(|c| c.title.as_deref())
-        .flatten()
+        .and_then(|c| c.title.as_deref())
         .unwrap_or(DEFAULT_TITLE)
 }
 

src/gui.rs

@@ -1,18 +1,20 @@
-use egui::{ClippedMesh, CtxRef, TextureId};
-use egui_wgpu_backend::{BackendError, RenderPass, ScreenDescriptor};
+use egui::{Context, TextureId};
+use egui_wgpu_backend::{wgpu, RenderPass, ScreenDescriptor};
 use egui_winit_platform::Platform;
 use wgpu::{
     Adapter, CommandEncoder, Device, Extent3d, FilterMode, Instance, Queue, RequestDeviceError,
-    Surface, SurfaceConfiguration, SurfaceTexture, Texture, TextureFormat, TextureUsages,
-    TextureView,
+    Surface, SurfaceCapabilities, SurfaceConfiguration, Texture, TextureView,
+    TextureViewDescriptor,
 };
+
+use winit::dpi::PhysicalSize;
 use winit::error::OsError;
-use winit::event::{ElementState, KeyboardInput};
-use winit::event_loop::EventLoop;
+use winit::event::{ElementState, Event, KeyboardInput};
+use winit::event_loop::{ControlFlow, EventLoop};
 use winit::window::Window;
 
 use crate::cpu::Cpu;
-use crate::{GB_HEIGHT, GB_WIDTH};
+use crate::{emu, GB_HEIGHT, GB_WIDTH};
 
 const EGUI_DIMENSIONS: (usize, usize) = (1280, 720);
 const FILTER_MODE: FilterMode = FilterMode::Nearest;
@@ -20,219 +22,163 @@ const WINDOW_TITLE: &str = "DMG-01 Emulator";
 
 const SCALE: f32 = 3.0;
 
-/// Holds GUI State
-#[derive(Debug, Clone)]
-pub struct GuiState {
-    /// When true, egui winit should exit the application
-    pub quit: bool,
+pub struct Gui {
+    pub should_quit: bool,
     pub title: String,
     pub mode: EmuMode,
+
+    window: Window,
+    platform: Platform,
+
+    surface: Surface,
+    device: Device,
+    queue: Queue,
+    surface_config: SurfaceConfiguration,
+    render_pass: RenderPass,
+
+    texture: Texture,
+    texture_size: Extent3d,
+    texture_id: TextureId,
 }
 
-impl GuiState {
-    pub fn new(title: String) -> Self {
+impl Gui {
+    pub fn new<T>(title: String, event_loop: &EventLoop<T>, cpu: &Cpu) -> Self {
+        use wgpu::InstanceDescriptor;
+
+        let window = build_window(event_loop).expect("build window");
+
+        let instance = Instance::new(InstanceDescriptor::default());
+        let surface = unsafe {
+            instance
+                .create_surface(&window)
+                .expect("create wgpu instance surface")
+        };
+
+        let adapter = request_adapter(&instance, &surface).expect("request adaptor");
+        let (device, queue) = request_device(&adapter).expect("request device");
+
+        let capabilities = surface.get_capabilities(&adapter);
+
+        let surface_config = surface_config(&window, capabilities);
+        surface.configure(&device, &surface_config);
+        let platform = platform(&window);
+        let mut render_pass = RenderPass::new(&device, surface_config.format, 1);
+
+        let texture_size = texture_size();
+        let texture = create_texture(&device, texture_size);
+        write_to_texture(&queue, &texture, emu::pixel_buf(cpu), texture_size);
+
+        let view = texture.create_view(&TextureViewDescriptor::default());
+        let texture_id = expose_texture_to_egui(&mut render_pass, &device, &view);
+
         Self {
+            should_quit: Default::default(),
             title,
-            quit: Default::default(),
             mode: EmuMode::Running,
-        }
-    }
-}
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum EmuMode {
-    Running,
-    StepFrame,
-    Stopped,
-    Step,
-}
+            window,
+            platform,
 
-/// To avoid using an [Option<KeyboardInput>] to keep track of user input from winit,
-/// we can use a "default" value. However, in order for this to work the chosen "default"
-/// value must be an **unused** key, so that it is ignored by the emulator.
-pub fn unused_key() -> KeyboardInput {
-    #![allow(deprecated)]
+            surface,
+            device,
+            queue,
+            surface_config,
+            render_pass,
 
-    KeyboardInput {
-        scancode: Default::default(),
-        state: ElementState::Released,
-        virtual_keycode: Default::default(),
-        modifiers: Default::default(), // this argument is deprecated
-    }
-}
-
-pub fn build_window<T>(event_loop: &EventLoop<T>) -> Result<Window, OsError> {
-    use winit::dpi::PhysicalSize;
-    use winit::window::WindowBuilder;
-
-    WindowBuilder::new()
-        .with_decorations(true)
-        .with_resizable(true)
-        .with_transparent(false)
-        .with_title(WINDOW_TITLE)
-        .with_inner_size(PhysicalSize {
-            width: EGUI_DIMENSIONS.0 as f32,
-            height: EGUI_DIMENSIONS.1 as f32,
-        })
-        .build(event_loop)
-}
-
-pub fn create_surface(window: &Window) -> (Instance, Surface) {
-    use wgpu::Backends;
-
-    let instance = Instance::new(Backends::PRIMARY);
-    let surface = unsafe { instance.create_surface(window) };
-    (instance, surface)
-}
-
-pub fn request_adapter(instance: &Instance, surface: &Surface) -> Option<Adapter> {
-    use wgpu::{PowerPreference, RequestAdapterOptions};
-
-    pollster::block_on(instance.request_adapter(&RequestAdapterOptions {
-        power_preference: PowerPreference::HighPerformance,
-        force_fallback_adapter: false, // TODO: What do I want to do with this?
-        compatible_surface: Some(surface),
-    }))
-}
-
-pub fn request_device(adapter: &Adapter) -> Result<(Device, Queue), RequestDeviceError> {
-    use wgpu::{DeviceDescriptor, Features, Limits};
-
-    pollster::block_on(adapter.request_device(
-        &DeviceDescriptor {
-            label: None,
-            features: Features::default(),
-            limits: Limits::default(),
-        },
-        None,
-    ))
-}
-
-pub fn surface_config(window: &Window, format: TextureFormat) -> SurfaceConfiguration {
-    use wgpu::PresentMode;
-
-    let size = window.inner_size();
-    SurfaceConfiguration {
-        usage: TextureUsages::RENDER_ATTACHMENT,
-        format,
-        width: size.width as u32,
-        height: size.height as u32,
-        present_mode: PresentMode::Mailbox,
-    }
-}
-
-pub fn platform_desc(window: &Window) -> Platform {
-    use egui::FontDefinitions;
-    use egui_winit_platform::PlatformDescriptor;
-
-    let size = window.inner_size();
-    Platform::new(PlatformDescriptor {
-        physical_width: size.width as u32,
-        physical_height: size.height as u32,
-        scale_factor: window.scale_factor(),
-        font_definitions: FontDefinitions::default(),
-        ..Default::default()
-    })
-}
-
-pub fn texture_size() -> Extent3d {
-    Extent3d {
-        width: GB_WIDTH as u32,
-        height: GB_HEIGHT as u32,
-        ..Default::default()
-    }
-}
-
-pub fn create_texture(device: &Device, size: Extent3d) -> Texture {
-    use wgpu::{TextureDescriptor, TextureDimension};
-
-    device.create_texture(&TextureDescriptor {
-        size,
-        mip_level_count: 1,
-        sample_count: 1,
-        dimension: TextureDimension::D2,
-        format: TextureFormat::Rgba8UnormSrgb,
-        usage: TextureUsages::COPY_DST | TextureUsages::TEXTURE_BINDING,
-        label: Some("gb_pixel_buffer"),
-    })
-}
-
-#[inline]
-pub fn write_to_texture(
-    queue: &Queue,
-    texture: &Texture,
-    data: &[u8; GB_WIDTH * 4 * GB_HEIGHT],
-    size: Extent3d,
-) {
-    use std::num::NonZeroU32;
-    use wgpu::{ImageCopyTexture, ImageDataLayout, Origin3d, TextureAspect};
-
-    queue.write_texture(
-        ImageCopyTexture {
             texture,
-            mip_level: 0,
-            origin: Origin3d::ZERO,
-            aspect: TextureAspect::All,
-        },
-        data,
-        ImageDataLayout {
-            offset: 0,
-            bytes_per_row: NonZeroU32::new(4 * GB_WIDTH as u32),
-            rows_per_image: NonZeroU32::new(GB_HEIGHT as u32),
-        },
-        size,
-    );
+            texture_size,
+            texture_id,
+        }
     }
 
-pub fn expose_texture_to_egui(
-    render_pass: &mut RenderPass,
-    device: &Device,
-    texture: &Texture,
-) -> TextureId {
-    render_pass.egui_texture_from_wgpu_texture(device, texture, FILTER_MODE)
+    pub fn maybe_quit(&self, cpu: &Cpu, control_flow: &mut ControlFlow) {
+        if self.should_quit {
+            emu::save_and_exit(cpu, control_flow);
+        }
+    }
+
+    pub fn request_redraw(&self) {
+        self.window.request_redraw();
+    }
+
+    pub fn handle_event<T>(&mut self, event: &Event<T>) {
+        self.platform.handle_event(event);
+    }
+
+    pub fn update_time(&mut self, elapsed_seconds: f64) {
+        self.platform.update_time(elapsed_seconds);
+    }
+
+    pub fn resize(&mut self, size: PhysicalSize<u32>) {
+        // See: https://github.com/rust-windowing/winit/issues/208
+        if size.width > 0 && size.height > 0 {
+            self.surface_config.width = size.width;
+            self.surface_config.height = size.height;
+            self.surface.configure(&self.device, &self.surface_config);
+        }
+    }
+
+    pub fn paint(&mut self, cpu: &Cpu) {
+        use wgpu::{Color, SurfaceError};
+
+        let data = emu::pixel_buf(cpu);
+        write_to_texture(&self.queue, &self.texture, data, self.texture_size);
+
+        let output_frame = match self.surface.get_current_texture() {
+            Ok(frame) => frame,
+            Err(SurfaceError::Outdated) => return, // Occurs on minimization on Windows
+            Err(e) => {
+                eprintln!("Dropped frame with error: {}", e);
+                return;
+            }
+        };
+
+        let output_view = output_frame
+            .texture
+            .create_view(&TextureViewDescriptor::default());
+
+        // Begin to draw Egui components
+        self.platform.begin_frame();
+        self.draw_egui(cpu, &self.platform.context(), self.texture_id);
+
+        // End the UI frame. We could now handle the output and draw the UI with the backend.
+        let full_output = self.platform.end_frame(Some(&self.window));
+        let paint_jobs = self.platform.context().tessellate(full_output.shapes);
+
+        let mut encoder = create_command_encoder(&self.device);
+        let screen_descriptor = create_screen_descriptor(&self.window, &self.surface_config);
+        let tdelta = full_output.textures_delta;
+        // Upload all resources for the GPU.
+        self.render_pass
+            .add_textures(&self.device, &self.queue, &tdelta)
+            .expect("add texture ok");
+        self.render_pass
+            .update_buffers(&self.device, &self.queue, &paint_jobs, &screen_descriptor);
+
+        // Record all render passes.
+        self.render_pass
+            .execute(
+                &mut encoder,
+                &output_view,
+                &paint_jobs,
+                &screen_descriptor,
+                Some(Color::BLACK),
+            )
+            .expect("execute render pass");
+
+        // Submit the commands.
+        self.queue.submit(std::iter::once(encoder.finish()));
+
+        // Redraw egui
+        output_frame.present();
+
+        self.render_pass
+            .remove_textures(tdelta)
+            .expect("remove texture delta");
     }
 
     #[inline]
-pub fn create_view(frame: &SurfaceTexture) -> TextureView {
-    use wgpu::TextureViewDescriptor;
-
-    frame.texture.create_view(&TextureViewDescriptor::default())
-}
-
-#[inline]
-pub fn create_command_encoder(device: &Device) -> CommandEncoder {
-    use wgpu::CommandEncoderDescriptor;
-
-    device.create_command_encoder(&CommandEncoderDescriptor {
-        label: Some("encoder"),
-    })
-}
-
-#[inline]
-pub fn create_screen_descriptor(
-    window: &Window,
-    config: &SurfaceConfiguration,
-) -> ScreenDescriptor {
-    ScreenDescriptor {
-        physical_width: config.width,
-        physical_height: config.height,
-        scale_factor: window.scale_factor() as f32,
-    }
-}
-
-#[inline]
-pub fn execute_render_pass(
-    render_pass: &mut RenderPass,
-    encoder: &mut CommandEncoder,
-    view: &TextureView,
-    jobs: Vec<ClippedMesh>,
-    descriptor: &ScreenDescriptor,
-) -> Result<(), BackendError> {
-    render_pass.execute(encoder, view, &jobs, descriptor, Some(wgpu::Color::BLACK))
-}
-
-#[inline]
-pub fn draw_egui(cpu: &Cpu, app: &mut GuiState, ctx: &CtxRef, texture_id: TextureId) {
+    pub fn draw_egui(&mut self, cpu: &Cpu, ctx: &Context, texture_id: TextureId) {
         use crate::{cpu, instruction, ppu};
 
         fn selectable_text(ui: &mut egui::Ui, mut text: &str) -> egui::Response {
@@ -240,13 +186,13 @@ pub fn draw_egui(cpu: &Cpu, app: &mut GuiState, ctx: &CtxRef, texture_id: Textur
         }
 
         egui::TopBottomPanel::top("top_panel").show(ctx, |ui| {
-        egui::menu::menu(ui, "File", |ui| {
+            ui.menu_button("File", |ui| {
                 if ui.button("Quit").clicked() {
-                app.quit = true;
+                    self.should_quit = true;
                 }
             });
 
-        egui::Window::new(&app.title).show(ctx, |ui| {
+            egui::Window::new(&self.title).show(ctx, |ui| {
                 ui.image(
                     texture_id,
                     [GB_WIDTH as f32 * SCALE, GB_HEIGHT as f32 * SCALE],
@@ -259,12 +205,12 @@ pub fn draw_egui(cpu: &Cpu, app: &mut GuiState, ctx: &CtxRef, texture_id: Textur
 
             egui::Window::new("Settings").show(ctx, |ui| {
                 egui::ComboBox::from_label("Emulation Mode")
-                .selected_text(format!("{:?}", app.mode))
+                    .selected_text(format!("{:?}", self.mode))
                     .show_ui(ui, |ui| {
-                    ui.selectable_value(&mut app.mode, EmuMode::Running, "Running");
-                    ui.selectable_value(&mut app.mode, EmuMode::Stopped, "Stopped");
-                    ui.selectable_value(&mut app.mode, EmuMode::StepFrame, "Step Frame");
-                    ui.selectable_value(&mut app.mode, EmuMode::Step, "Step");
+                        ui.selectable_value(&mut self.mode, EmuMode::Running, "Running");
+                        ui.selectable_value(&mut self.mode, EmuMode::Stopped, "Stopped");
+                        ui.selectable_value(&mut self.mode, EmuMode::StepFrame, "Step Frame");
+                        ui.selectable_value(&mut self.mode, EmuMode::Step, "Step");
                     })
             });
 
@@ -297,7 +243,11 @@ pub fn draw_egui(cpu: &Cpu, app: &mut GuiState, ctx: &CtxRef, texture_id: Textur
                             ui.monospace(format!("WY: {}", ppu::dbg::wy(ppu)));
                         });
 
-                    ui.monospace(format!("Mode: {:?}", ppu::dbg::mode(ppu)))
+                        ui.monospace(format!(
+                            "Mode: {:?} {}",
+                            ppu::dbg::mode(ppu),
+                            ppu::dbg::dot(ppu)
+                        ))
                     });
                 });
 
@@ -318,12 +268,13 @@ pub fn draw_egui(cpu: &Cpu, app: &mut GuiState, ctx: &CtxRef, texture_id: Textur
                 ui.horizontal(|ui| {
                     let ie = cpu.int_enable();
 
-                let r_len = ctx.fonts().glyph_width(egui::TextStyle::Body, 'R');
-                let e_len = ctx.fonts().glyph_width(egui::TextStyle::Body, 'E');
-                let q_len = ctx.fonts().glyph_width(egui::TextStyle::Body, 'Q');
+                    // TODO: Reimplement this
+                    // let r_len = ctx.fonts().glyph_width(egui::TextStyle::Body, 'R');
+                    // let e_len = ctx.fonts().glyph_width(egui::TextStyle::Body, 'E');
+                    // let q_len = ctx.fonts().glyph_width(egui::TextStyle::Body, 'Q');
 
                     ui.label("IE:");
-                ui.add_space(q_len - (e_len - r_len));
+                    // ui.add_space(q_len - (e_len - r_len));
                     let _ = ui.selectable_label(ie & 0b01 == 0x01, "VBlank");
                     let _ = ui.selectable_label(ie >> 1 & 0x01 == 0x01, "LCD STAT");
                     let _ = ui.selectable_label(ie >> 2 & 0x01 == 0x01, "Timer");
@@ -344,6 +295,172 @@ pub fn draw_egui(cpu: &Cpu, app: &mut GuiState, ctx: &CtxRef, texture_id: Textur
             })
         });
     }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum EmuMode {
+    Running,
+    StepFrame,
+    Stopped,
+    Step,
+}
+
+/// To avoid using an [Option<KeyboardInput>] to keep track of user input from winit,
+/// we can use a "default" value. However, in order for this to work the chosen "default"
+/// value must be an **unused** key, so that it is ignored by the emulator.
+pub fn unused_key() -> KeyboardInput {
+    #![allow(deprecated)]
+
+    KeyboardInput {
+        scancode: Default::default(),
+        state: ElementState::Released,
+        virtual_keycode: Default::default(),
+        modifiers: Default::default(), // this argument is deprecated
+    }
+}
+
+fn build_window<T>(event_loop: &EventLoop<T>) -> Result<Window, OsError> {
+    use winit::window::WindowBuilder;
+
+    WindowBuilder::new()
+        .with_decorations(true)
+        .with_resizable(true)
+        .with_transparent(false)
+        .with_title(WINDOW_TITLE)
+        .with_inner_size(PhysicalSize {
+            width: EGUI_DIMENSIONS.0 as f32,
+            height: EGUI_DIMENSIONS.1 as f32,
+        })
+        .build(event_loop)
+}
+
+fn request_adapter(instance: &Instance, surface: &Surface) -> Option<Adapter> {
+    use wgpu::{PowerPreference, RequestAdapterOptions};
+
+    pollster::block_on(instance.request_adapter(&RequestAdapterOptions {
+        power_preference: PowerPreference::HighPerformance,
+        compatible_surface: Some(surface),
+        force_fallback_adapter: false, // TODO: What do I want to do with this?
+    }))
+}
+
+fn request_device(adapter: &Adapter) -> Result<(Device, Queue), RequestDeviceError> {
+    use wgpu::{DeviceDescriptor, Features, Limits};
+
+    pollster::block_on(adapter.request_device(
+        &DeviceDescriptor {
+            features: Features::default(),
+            limits: Limits::default(),
+            label: None,
+        },
+        None,
+    ))
+}
+
+fn surface_config(window: &Window, capabilities: SurfaceCapabilities) -> SurfaceConfiguration {
+    use egui_wgpu_backend::wgpu::{PresentMode, TextureFormat, TextureUsages};
+
+    let size = window.inner_size();
+    SurfaceConfiguration {
+        usage: TextureUsages::RENDER_ATTACHMENT,
+        format: capabilities.formats[0],
+        width: size.width as u32,
+        height: size.height as u32,
+        present_mode: PresentMode::Fifo,
+        alpha_mode: capabilities.alpha_modes[0],
+        view_formats: vec![TextureFormat::Rgba8UnormSrgb],
+    }
+}
+
+fn platform(window: &Window) -> Platform {
+    use egui::FontDefinitions;
+    use egui_winit_platform::PlatformDescriptor;
+
+    let size = window.inner_size();
+    Platform::new(PlatformDescriptor {
+        physical_width: size.width as u32,
+        physical_height: size.height as u32,
+        scale_factor: window.scale_factor(),
+        font_definitions: FontDefinitions::default(),
+        ..Default::default()
+    })
+}
+
+fn texture_size() -> Extent3d {
+    Extent3d {
+        width: GB_WIDTH as u32,
+        height: GB_HEIGHT as u32,
+        ..Default::default()
+    }
+}
+
+fn create_texture(device: &Device, size: Extent3d) -> Texture {
+    use wgpu::{TextureDescriptor, TextureDimension, TextureFormat, TextureUsages};
+
+    device.create_texture(&TextureDescriptor {
+        size,
+        mip_level_count: 1,
+        sample_count: 1,
+        dimension: TextureDimension::D2,
+        format: TextureFormat::Bgra8Unorm,
+        usage: TextureUsages::COPY_DST | TextureUsages::TEXTURE_BINDING,
+        label: Some("gb_pixel_buffer"),
+        view_formats: &[TextureFormat::Bgra8Unorm],
+    })
+}
+
+#[inline]
+fn write_to_texture(
+    queue: &Queue,
+    texture: &Texture,
+    data: &[u8; GB_WIDTH * 4 * GB_HEIGHT],
+    size: Extent3d,
+) {
+    use std::num::NonZeroU32;
+    use wgpu::{ImageCopyTexture, ImageDataLayout, Origin3d, TextureAspect};
+
+    queue.write_texture(
+        ImageCopyTexture {
+            texture,
+            mip_level: 0,
+            origin: Origin3d::ZERO,
+            aspect: TextureAspect::All,
+        },
+        data,
+        ImageDataLayout {
+            offset: 0,
+            bytes_per_row: NonZeroU32::new(4 * GB_WIDTH as u32),
+            rows_per_image: NonZeroU32::new(GB_HEIGHT as u32),
+        },
+        size,
+    );
+}
+
+fn expose_texture_to_egui(
+    render_pass: &mut RenderPass,
+    device: &Device,
+    view: &TextureView,
+) -> TextureId {
+    render_pass.egui_texture_from_wgpu_texture(device, view, FILTER_MODE)
+}
+
+#[inline]
+fn create_command_encoder(device: &Device) -> CommandEncoder {
+    use wgpu::CommandEncoderDescriptor;
+
+    device.create_command_encoder(&CommandEncoderDescriptor {
+        label: Some("encoder"),
+    })
+}
+
+#[inline]
+fn create_screen_descriptor(window: &Window, config: &SurfaceConfiguration) -> ScreenDescriptor {
+    ScreenDescriptor {
+        physical_width: config.width,
+        physical_height: config.height,
+        scale_factor: window.scale_factor() as f32,
+    }
+}
 
 pub mod kbd {
     use winit::event::{ElementState, KeyboardInput, VirtualKeyCode};

src/instruction.rs

@@ -1654,7 +1654,9 @@ impl Instruction {
             0o304 | 0o314 | 0o324 | 0o334 => CALL(jump_cond((byte >> 3) & 0x03)),
             // PUSH r16
             0o305 | 0o325 | 0o345 | 0o365 => PUSH(group3((byte >> 4) & 0x03)),
+            // CALL u16
             0o315 => CALL(JpCond::Always),
+            // ADD, ADC, SUB, SBC, AND, XOR, OR, and CP
             0o306 | 0o316 | 0o326 | 0o336 | 0o346 | 0o356 | 0o366 | 0o376 => {
                 alu_imm_instr((byte >> 3) & 0x07)
             }
@@ -2071,7 +2073,7 @@ mod table {
             0b101 => L,
             0b110 => IndirectHL,
             0b111 => A,
-            _ => unreachable!("{:#04X} is not a valid Register"),
+            _ => unreachable!("{:#04X} is not a valid Register", code),
         }
     }
 
@@ -2153,8 +2155,11 @@ mod table {
 }
 
 pub(crate) mod dbg {
+    use std::borrow::Cow;
+
     use super::add::{Source as AddSource, Target as AddTarget};
-    use super::jump::JpCond;
+    use super::alu::Source as AluSource;
+    use super::jump::{JpCond, JpLoc};
     use super::load::{Source as LDSource, Target as LDTarget};
     use super::{AllRegisters, BusIo, Cpu, Instruction, RegisterPair};
 
@@ -2188,28 +2193,140 @@ pub(crate) mod dbg {
         sm83_asm
     }
 
-    fn disasm(cpu: &Cpu, pc: u16, instr: Instruction) -> String {
+    pub(crate) fn new_disasm(cpu: &Cpu, limit: u8) -> String {
+        let mut assembly = String::new();
+        let mut pc = cpu.register_pair(RegisterPair::PC);
+
+        for _ in 0..limit {
+            let opcode = cpu.read_byte(pc);
+            pc += 1;
+
+            let maybe_instr = if opcode == 0xCB {
+                let opcode = cpu.read_byte(pc);
+                pc += 1;
+
+                Instruction::prefixed(opcode)
+            } else {
+                Instruction::unprefixed(opcode)
+            };
+
+            match maybe_instr {
+                Instruction::Invalid => {}
+                instr => {
+                    let output = format!("${:04X} {}\n", pc - 1, disasm(cpu, pc, instr));
+                    assembly.push_str(&output);
+                    pc += delta::pc_inc_count(instr);
+                }
+            }
+        }
+
+        assembly
+    }
+
+    // TODO: It might be better if I pass in a mutable writer instead of usnig a String
+    fn disasm(cpu: &Cpu, pc: u16, instr: Instruction) -> Cow<str> {
         use Instruction::*;
 
         let imm_byte = cpu.read_byte(pc + 1);
         let imm_word = (cpu.read_byte(pc + 2) as u16) << 8 | imm_byte as u16;
 
         match instr {
-            NOP => "NOP".to_string(),
+            // Unprefixed Instructions
+            NOP => "NOP".into(),
             LD(LDTarget::IndirectImmediateWord, LDSource::SP) => {
-                format!("LD ({:#06X}), SP", imm_word)
+                format!("LD ({:#06X}), SP", imm_word).into()
             }
-            STOP => "STOP".to_string(),
-            JR(JpCond::Always) => format!("JR {}", imm_byte as i8),
-            JR(cond) => format!("JR {:?} {}", cond, imm_byte as i8),
+            STOP => "STOP".into(),
+            JR(JpCond::Always) => format!("JR {}", imm_byte as i8).into(),
+            JR(cond) => format!("JR {:?} {}", cond, imm_byte as i8).into(),
             LD(LDTarget::Group1(rp), LDSource::ImmediateWord) => {
-                format!("LD {:?} {:#06X}", rp, imm_word)
+                format!("LD {:?} {:#06X}", rp, imm_word).into()
             }
-            ADD(AddTarget::HL, AddSource::Group1(rp)) => format!("ADD HL, {:?}", rp),
-            LD(LDTarget::IndirectGroup2(rp), LDSource::A) => format!("LD ({:?}), A", rp),
-            LD(LDTarget::A, LDSource::IndirectGroup2(rp)) => format!("LD A, ({:?})", rp),
+            ADD(AddTarget::HL, AddSource::Group1(rp)) => format!("ADD HL, {:?}", rp).into(),
+            LD(LDTarget::IndirectGroup2(rp), LDSource::A) => format!("LD ({:?}), A", rp).into(),
+            LD(LDTarget::A, LDSource::IndirectGroup2(rp)) => format!("LD A, ({:?})", rp).into(),
+            INC(AllRegisters::Group1(rp)) => format!("INC {:?}", rp).into(),
+            DEC(AllRegisters::Group1(rp)) => format!("DEC {:?}", rp).into(),
+            INC(AllRegisters::Register(reg)) => format!("INC {:?}", reg).into(),
+            DEC(AllRegisters::Register(reg)) => format!("DEC {:?}", reg).into(),
+            LD(LDTarget::Register(reg), LDSource::ImmediateByte) => {
+                format!("LD {:?}, {:#04X}", reg, imm_byte).into()
+            }
+            RLCA => "RLCA".into(),
+            RRCA => "RRCA".into(),
+            RLA => "RLA".into(),
+            RRA => "RRA".into(),
+            DAA => "DAA".into(),
+            CPL => "CPL".into(),
+            SCF => "SCF".into(),
+            CCF => "CCF".into(),
+            HALT => "HALT".into(),
+            LD(LDTarget::Register(left), LDSource::Register(right)) => {
+                format!("LD {:?}, {:?}", left, right).into()
+            }
+            ADD(AddTarget::A, AddSource::Register(reg)) => format!("ADD A, {:?}", reg).into(),
+            ADC(AluSource::Register(reg)) => format!("ADC {:?}", reg).into(),
+            SUB(AluSource::Register(reg)) => format!("SUB {:?}", reg).into(),
+            SBC(AluSource::Register(reg)) => format!("SBC {:?}", reg).into(),
+            AND(AluSource::Register(reg)) => format!("AND {:?}", reg).into(),
+            XOR(AluSource::Register(reg)) => format!("XOR {:?}", reg).into(),
+            OR(AluSource::Register(reg)) => format!("OR {:?}", reg).into(),
+            CP(AluSource::Register(reg)) => format!("CP {:?}", reg).into(),
+            RET(JpCond::Always) => "RET".into(),
+            RET(cond) => format!("RET {:?}", cond).into(),
+            LD(LDTarget::IoWithImmediateOffset, LDSource::A) => {
+                format!("LD ({:#06X}) , A", 0xFF00 + imm_byte as u16).into()
+            }
+            ADD(AddTarget::SP, AddSource::ImmediateSignedByte) => {
+                format!("ADD SP, {}", imm_byte as i8).into()
+            }
+            LD(LDTarget::A, LDSource::IoWithImmediateOffset) => {
+                format!("LD A, ({:#06X})", 0xFF00 + imm_byte as u16).into()
+            }
+            LDHL => format!("LD HL, SP + {}", imm_byte as i8).into(),
+            POP(rp) => format!("POP {:?}", rp).into(),
+            RETI => "RETI".into(),
+            JP(JpCond::Always, JpLoc::HL) => "JP HL".into(),
+            LD(LDTarget::SP, LDSource::HL) => "LD SP, HL".into(),
+            JP(JpCond::Always, JpLoc::ImmediateWord) => format!("JP {:#06X}", imm_word).into(),
+            JP(cond, JpLoc::ImmediateWord) => format!("JP {:?} {:#06X}", cond, imm_word).into(),
+            LD(LDTarget::IoWithC, LDSource::A) => "LD (0xFF00 + C), A".into(),
+            LD(LDTarget::IndirectImmediateWord, LDSource::A) => {
+                format!("LD ({:#06X}), A", imm_byte).into()
+            }
+            LD(LDTarget::A, LDSource::IoWithC) => "LD A, (0xFF00 + C)".into(),
+            LD(LDTarget::A, LDSource::IndirectImmediateWord) => {
+                format!("LD A, ({:#06X})", imm_word).into()
+            }
+            DI => "DI".into(),
+            EI => "EI".into(),
+            CALL(cond) => format!("CALL {:?} {:#06X}", cond, imm_word).into(),
+            PUSH(rp) => format!("PUSH {:?}", rp).into(),
+            ADD(AddTarget::A, AddSource::ImmediateByte) => {
+                format!("ADD A, {:#04X}", imm_byte).into()
+            }
+            ADC(AluSource::ImmediateByte) => format!("ADC {:#04X}", imm_byte).into(),
+            SUB(AluSource::ImmediateByte) => format!("SUB {:#04X}", imm_byte).into(),
+            SBC(AluSource::ImmediateByte) => format!("SBC {:#04X}", imm_byte).into(),
+            AND(AluSource::ImmediateByte) => format!("AND {:#04X}", imm_byte).into(),
+            XOR(AluSource::ImmediateByte) => format!("XOR {:#04X}", imm_byte).into(),
+            OR(AluSource::ImmediateByte) => format!("OR {:#04X}", imm_byte).into(),
+            CP(AluSource::ImmediateByte) => format!("CP {:#04X}", imm_byte).into(),
+            RST(v) => format!("RST {:#04X}", v).into(),
 
-            _ => todo!(),
+            // Prefixed Instructions
+            RLC(reg) => format!("RLC {:?}", reg).into(),
+            RRC(reg) => format!("RRC {:?}", reg).into(),
+            RL(reg) => format!("RL {:?}", reg).into(),
+            RR(reg) => format!("RR {:?}", reg).into(),
+            SLA(reg) => format!("SLA {:?}", reg).into(),
+            SRA(reg) => format!("SRA {:?}", reg).into(),
+            SWAP(reg) => format!("SWAP {:?}", reg).into(),
+            SRL(reg) => format!("SRL {:?}", reg).into(),
+            BIT(bit, reg) => format!("BIT {}, {:?}", bit, reg).into(),
+            RES(bit, reg) => format!("RES {}, {:?}", bit, reg).into(),
+            SET(bit, reg) => format!("SET {}, {:?}", bit, reg).into(),
+            _ => unreachable!("{:?} is an illegal instruction", instr),
         }
     }
 

src/main.rs

@@ -1,39 +1,28 @@
+use std::path::PathBuf;
 use std::time::Instant;
 
-use clap::{crate_authors, crate_description, crate_name, crate_version, App, Arg};
-use egui_wgpu_backend::RenderPass;
-use gb::gui::EmuMode;
+use clap::{arg, command, value_parser};
+use gb::gui::{EmuMode, Gui};
 use gb::{emu, gui};
 use gilrs::Gilrs;
-use gui::GuiState;
 use rodio::{OutputStream, Sink};
 use tracing_subscriber::EnvFilter;
 use winit::event::{Event, WindowEvent};
-use winit::event_loop::EventLoop;
+use winit::event_loop::{EventLoop, EventLoopBuilder};
 
 const AUDIO_ENABLED: bool = true;
 
 fn main() {
-    let app = App::new(crate_name!())
-        .version(crate_version!())
-        .author(crate_authors!())
-        .about(crate_description!());
-
-    let m = app
+    let m = command!()
         .arg(
-            Arg::with_name("rom")
-                .value_name("ROM_FILE")
-                .takes_value(true)
-                .index(1)
-                .help("Path to the Game ROM"),
+            arg!(-b --boot <FILE> "path to boot ROM")
+                .required(false)
+                .value_parser(value_parser!(PathBuf)),
         )
         .arg(
-            Arg::with_name("boot")
-                .short("b")
-                .long("boot")
-                .value_name("FILE")
-                .takes_value(true)
-                .help("Path to Boot ROM"),
+            arg!([ROM_FILE] "path to game ROM")
+                .required(true)
+                .value_parser(value_parser!(PathBuf)),
         )
         .get_matches();
 
@@ -46,25 +35,8 @@ fn main() {
         .with_env_filter(EnvFilter::from_default_env())
         .init();
 
-    // --Here lies a lot of winit + wgpu Boilerplate--
-    let event_loop: EventLoop<Event<()>> = EventLoop::with_user_event();
-    let window = gui::build_window(&event_loop).expect("build window");
-
-    let (instance, surface) = gui::create_surface(&window);
-    let adapter = gui::request_adapter(&instance, &surface).expect("request adaptor");
-    let (device, queue) = gui::request_device(&adapter).expect("request device");
-    let format = surface
-        .get_preferred_format(&adapter)
-        .expect("get surface format");
-
-    let mut config = gui::surface_config(&window, format);
-    surface.configure(&device, &config);
-    let mut platform = gui::platform_desc(&window);
-    let mut render_pass = RenderPass::new(&device, format, 1);
-
-    // We interrupt your boiler plate to initialize the emulator so that
-    // we can copy it's empty pixel buffer to the GPU
-    let mut cpu = match m.value_of("boot") {
+    // Init CPU
+    let mut cpu = match m.get_one::<PathBuf>("boot") {
         Some(path) => {
             tracing::info!("User-provided boot ROM");
             emu::from_boot_rom(path).expect("initialize emulator with custom boot rom")
@@ -75,20 +47,12 @@ fn main() {
         }
     };
 
-    // Set up the wgpu (and then EGUI) texture we'll be working with.
-    let texture_size = gui::texture_size();
-    let texture = gui::create_texture(&device, texture_size);
-    gui::write_to_texture(&queue, &texture, emu::pixel_buf(&cpu), texture_size);
-    let texture_id = gui::expose_texture_to_egui(&mut render_pass, &device, &texture);
-
     // Load ROM if filepath was provided
-    if let Some(path) = m.value_of("rom") {
+    if let Some(path) = m.get_one::<PathBuf>("ROM_FILE") {
         tracing::info!("User-provided cartridge ROM");
         emu::read_game_rom(&mut cpu, path).expect("read game rom from path");
     }
-
     emu::load_save(&mut cpu);
-
     let rom_title = emu::rom_title(&cpu).to_string();
 
     tracing::info!("Initialize Gamepad");
@@ -115,20 +79,20 @@ fn main() {
     }
 
     // Set up state for the Immediate-mode GUI
-    let mut app = GuiState::new(rom_title);
-    let mut last_key = gui::unused_key();
+    let event_loop: EventLoop<Event<()>> = EventLoopBuilder::with_user_event().build();
+
+    let mut app = Gui::new(rom_title, &event_loop, &cpu);
+    let mut last_key = gui::unused_key(); // TODO: Fix this awful impl
 
     // used for egui animations
     let start_time = Instant::now();
 
     event_loop.run(move |event, _, control_flow| {
-        platform.handle_event(&event);
+        app.handle_event(&event);
 
         match event {
             Event::MainEventsCleared => {
-                if app.quit {
-                    emu::save_and_exit(&cpu, control_flow);
-                }
+                app.maybe_quit(&cpu, control_flow);
 
                 match app.mode {
                     EmuMode::Running => emu::run_frame(&mut cpu, &mut gamepad, last_key),
@@ -144,63 +108,15 @@ fn main() {
                 // Input has been consumed, reset it
                 last_key = gui::unused_key();
 
-                window.request_redraw();
+                app.request_redraw();
             }
             Event::RedrawRequested(..) => {
-                platform.update_time(start_time.elapsed().as_secs_f64());
-
-                let data = emu::pixel_buf(&cpu);
-                gui::write_to_texture(&queue, &texture, data, texture_size);
-
-                let output_frame = match surface.get_current_texture() {
-                    Ok(frame) => frame,
-                    Err(e) => {
-                        eprintln!("Dropped frame with error: {}", e);
-                        return;
-                    }
-                };
-                let output_view = gui::create_view(&output_frame);
-
-                // Begin to draw Egui components
-                platform.begin_frame();
-                gui::draw_egui(&cpu, &mut app, &platform.context(), texture_id);
-                // End the UI frame. We could now handle the output and draw the UI with the backend.
-                let (_, paint_commands) = platform.end_frame(Some(&window));
-                let paint_jobs = platform.context().tessellate(paint_commands);
-
-                let mut encoder = gui::create_command_encoder(&device);
-                let screen_descriptor = gui::create_screen_descriptor(&window, &config);
-
-                // Upload all resources for the GPU.
-                render_pass.update_texture(&device, &queue, &platform.context().texture());
-                render_pass.update_user_textures(&device, &queue);
-                render_pass.update_buffers(&device, &queue, &paint_jobs, &screen_descriptor);
-
-                // Record all render passes.
-                gui::execute_render_pass(
-                    &mut render_pass,
-                    &mut encoder,
-                    &output_view,
-                    paint_jobs,
-                    &screen_descriptor,
-                )
-                .expect("record render passes");
-
-                // Submit the commands.
-                queue.submit(std::iter::once(encoder.finish()));
-
-                // Redraw egui
-                output_frame.present();
+                app.update_time(start_time.elapsed().as_secs_f64());
+                app.paint(&cpu);
             }
             Event::WindowEvent { event, .. } => match event {
-                WindowEvent::Resized(size) => {
-                    config.width = size.width;
-                    config.height = size.height;
-                    surface.configure(&device, &config);
-                }
-                WindowEvent::CloseRequested => {
-                    emu::save_and_exit(&cpu, control_flow);
-                }
+                WindowEvent::Resized(size) => app.resize(size),
+                WindowEvent::CloseRequested => emu::save_and_exit(&cpu, control_flow),
                 WindowEvent::KeyboardInput { input, .. } => last_key = input,
                 _ => {}
             },

src/ppu.rs

@@ -10,6 +10,8 @@ use types::{
     ObjectPaletteKind, ObjectSize, Pixels, RenderPriority, TileDataAddress,
 };
 
+use once_cell::sync::Lazy;
+
 mod dma;
 mod types;
 
@@ -32,6 +34,14 @@ const LIGHT_GRAY: [u8; 4] = 0xAEBA89FFu32.to_be_bytes();
 const DARK_GRAY: [u8; 4] = 0x5E6745FFu32.to_be_bytes();
 const BLACK: [u8; 4] = 0x202020FFu32.to_be_bytes();
 
+static BLANK_SCREEN: Lazy<Box<[u8; (GB_WIDTH * 4) * GB_HEIGHT]>> = Lazy::new(|| {
+    WHITE
+        .repeat(GB_WIDTH * GB_HEIGHT)
+        .into_boxed_slice()
+        .try_into()
+        .unwrap()
+});
+
 #[derive(Debug)]
 pub struct Ppu {
     pub(crate) int: Interrupt,
@@ -48,7 +58,7 @@ pub struct Ppu {
     fetch: PixelFetcher,
     fifo: PixelFifo,
     obj_buffer: ObjectBuffer,
-    pub(crate) frame_buf: Box<[u8; GB_WIDTH * GB_HEIGHT * 4]>,
+    pub(crate) frame_buf: FrameBuffer,
     win_stat: WindowStatus,
 
     scanline_start: bool,
@@ -70,15 +80,26 @@ impl BusIo for Ppu {
 
 impl Ppu {
     pub(crate) fn tick(&mut self) {
-        self.dot += 1;
-
         if !self.ctrl.lcd_enabled() {
+            if self.dot > 0 {
+                // Check ensures this expensive operation only happens once
+                self.frame_buf
+                    .get_mut(Device::Guest)
+                    .copy_from_slice(BLANK_SCREEN.as_ref());
+            }
+
+            self.stat.set_mode(PpuMode::HBlank);
+            self.pos.line_y = 0;
+            self.dot = 0;
             return;
         }
 
+        self.dot += 1;
+
         match self.stat.mode() {
             PpuMode::OamScan => {
                 // Cycles 1 -> 80
+
                 if self.dot >= 80 {
                     self.x_pos = 0;
                     self.scanline_start = true;
@@ -104,12 +125,7 @@ impl Ppu {
                 self.scan_oam();
             }
             PpuMode::Drawing => {
-                if self.ctrl.lcd_enabled() {
-                    // Only Draw when the LCD Is Enabled
                 self.draw();
-                } else {
-                    self.reset();
-                }
 
                 if self.x_pos == 160 {
                     if self.stat.hblank_int() {
@@ -164,6 +180,9 @@ impl Ppu {
                             self.int.set_lcd_stat(true);
                         }
 
+                        // Screen is done drawing
+                        self.frame_buf.swap();
+
                         PpuMode::VBlank
                     } else {
                         if self.stat.oam_int() {
@@ -397,8 +416,8 @@ impl Ppu {
                 let x = self.x_pos as usize;
 
                 let i = (GB_WIDTH * 4) * y + (x * 4);
-                self.frame_buf[i..(i + rgba.len())].copy_from_slice(&rgba);
 
+                self.frame_buf.get_mut(Device::Guest)[i..(i + rgba.len())].copy_from_slice(&rgba);
                 self.x_pos += 1;
             }
 
@@ -415,14 +434,6 @@ impl Ppu {
         }
     }
 
-    fn reset(&mut self) {
-        self.pos.line_y = 0;
-        self.stat.set_mode(PpuMode::HBlank);
-
-        let mut blank = WHITE.repeat(self.frame_buf.len() / 4);
-        self.frame_buf.swap_with_slice(&mut blank);
-    }
-
     fn clock_fifo(&mut self) -> Option<GrayShade> {
         use RenderPriority::*;
 
@@ -468,7 +479,7 @@ impl Default for Ppu {
         Self {
             vram: Box::new([0u8; VRAM_SIZE]),
             dot: Default::default(),
-            frame_buf: Box::new([0; GB_WIDTH * GB_HEIGHT * 4]),
+            frame_buf: FrameBuffer::new().expect("create frame buffers"),
             int: Default::default(),
             ctrl: LCDControl(0),
             monochrome: Default::default(),
@@ -913,6 +924,7 @@ struct WindowStatus {
 
 pub(crate) mod dbg {
     use super::{Ppu, PpuMode};
+    use crate::Cycle;
 
     pub(crate) fn ly(ppu: &Ppu) -> u8 {
         ppu.pos.line_y
@@ -937,4 +949,68 @@ pub(crate) mod dbg {
     pub(crate) fn wy(ppu: &Ppu) -> i16 {
         ppu.pos.window_y as i16
     }
+
+    pub(crate) fn dot(ppu: &Ppu) -> Cycle {
+        ppu.dot
+    }
+}
+
+#[derive(Debug)]
+pub struct FrameBuffer {
+    buf: [Box<[u8; Self::FRAME_LEN]>; 2],
+    current: bool,
+}
+
+#[derive(PartialEq)]
+pub enum Device {
+    Guest,
+    Host,
+}
+
+impl FrameBuffer {
+    const FRAME_LEN: usize = GB_WIDTH * std::mem::size_of::<u32>() * GB_HEIGHT;
+
+    pub fn new() -> Result<Self, FrameBufferError> {
+        Ok(Self {
+            buf: [
+                vec![0; Self::FRAME_LEN]
+                    .into_boxed_slice()
+                    .try_into()
+                    .map_err(|_| FrameBufferError::TryFrom)?,
+                vec![0; Self::FRAME_LEN]
+                    .into_boxed_slice()
+                    .try_into()
+                    .map_err(|_| FrameBufferError::TryFrom)?,
+            ],
+            current: false,
+        })
+    }
+
+    pub fn swap(&mut self) {
+        self.current = !self.current;
+    }
+
+    pub fn get_mut(&mut self, device: Device) -> &mut [u8; Self::FRAME_LEN] {
+        let idx = match device {
+            Device::Guest => self.current,
+            Device::Host => !self.current,
+        };
+
+        &mut *self.buf[idx as usize]
+    }
+
+    pub fn get(&self, device: Device) -> &[u8; Self::FRAME_LEN] {
+        let idx = match device {
+            Device::Guest => self.current,
+            Device::Host => !self.current,
+        };
+
+        &*self.buf[idx as usize]
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum FrameBufferError {
+    #[error("Failed to coerce boxed slice to boxed array")]
+    TryFrom,
 }

src/ppu/types.rs

@@ -335,7 +335,7 @@ impl From<ObjectPaletteKind> for u8 {
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq)]
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
 pub enum RenderPriority {
     Object = 0,
     BackgroundAndWindow = 1,