Render images on background thread to keep UI responsive

Cargo.toml

@@ -35,7 +35,7 @@ rubato = "0.16"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 thread-priority = "1"
-tokio = { version = "1", features = ["io-util", "macros", "net", "rt", "sync"] }
+tokio = { version = "1", features = ["io-util", "macros", "net", "rt", "sync", "time"] }
 tracing = { version = "0.1", features = ["release_max_level_info"] }
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 wgpu = "23"

src/app.rs

@@ -18,8 +18,13 @@ use crate::{
     controller::ControllerManager,
     emulator::{EmulatorClient, EmulatorCommand, SimId},
     input::MappingProvider,
+    memory::MemoryMonitor,
     persistence::Persistence,
-    window::{AboutWindow, AppWindow, GameWindow, GdbServerWindow, InputWindow},
+    vram::VramProcessor,
+    window::{
+        AboutWindow, AppWindow, BgMapWindow, CharacterDataWindow, GameWindow, GdbServerWindow,
+        InputWindow,
+    },
 };
 
 fn load_icon() -> anyhow::Result<IconData> {
@@ -39,6 +44,8 @@ pub struct Application {
     proxy: EventLoopProxy<UserEvent>,
     mappings: MappingProvider,
     controllers: ControllerManager,
+    memory: MemoryMonitor,
+    vram: VramProcessor,
     persistence: Persistence,
     viewports: HashMap<ViewportId, Viewport>,
     focused: Option<ViewportId>,
@@ -55,6 +62,8 @@ impl Application {
         let persistence = Persistence::new();
         let mappings = MappingProvider::new(persistence.clone());
         let controllers = ControllerManager::new(client.clone(), &mappings);
+        let memory = MemoryMonitor::new(client.clone());
+        let vram = VramProcessor::new();
         {
             let mappings = mappings.clone();
             let proxy = proxy.clone();
@@ -65,6 +74,8 @@ impl Application {
             client,
             proxy,
             mappings,
+            memory,
+            vram,
             controllers,
             persistence,
             viewports: HashMap::new(),
@@ -194,6 +205,14 @@ impl ApplicationHandler<UserEvent> for Application {
                 let about = AboutWindow;
                 self.open(event_loop, Box::new(about));
             }
+            UserEvent::OpenCharacterData(sim_id) => {
+                let vram = CharacterDataWindow::new(sim_id, &mut self.memory, &mut self.vram);
+                self.open(event_loop, Box::new(vram));
+            }
+            UserEvent::OpenBgMap(sim_id) => {
+                let bgmap = BgMapWindow::new(sim_id, &mut self.memory, &mut self.vram);
+                self.open(event_loop, Box::new(bgmap));
+            }
             UserEvent::OpenDebugger(sim_id) => {
                 let debugger =
                     GdbServerWindow::new(sim_id, self.client.clone(), self.proxy.clone());
@@ -300,7 +319,7 @@ impl Viewport {
         let (window, state) = create_window_and_state(&ctx, event_loop, &builder, &mut painter);
         egui_winit::update_viewport_info(&mut info, &ctx, &window, true);
 
-        app.on_init(painter.render_state().as_ref().unwrap());
+        app.on_init(&ctx, painter.render_state().as_ref().unwrap());
         Self {
             painter,
             ctx,
@@ -403,6 +422,8 @@ impl Drop for Viewport {
 pub enum UserEvent {
     GamepadEvent(gilrs::Event),
     OpenAbout,
+    OpenCharacterData(SimId),
+    OpenBgMap(SimId),
     OpenDebugger(SimId),
     OpenInput,
     OpenPlayer2,

src/main.rs

@@ -19,7 +19,9 @@ mod emulator;
 mod gdbserver;
 mod graphics;
 mod input;
+mod memory;
 mod persistence;
+mod vram;
 mod window;
 
 #[derive(Parser)]

src/memory.rs

@@ -0,0 +1,91 @@
+use std::{
+    collections::HashMap,
+    sync::{Arc, Mutex, MutexGuard},
+};
+
+use bytemuck::BoxBytes;
+
+use crate::emulator::{EmulatorClient, EmulatorCommand, SimId};
+
+pub struct MemoryMonitor {
+    client: EmulatorClient,
+    regions: HashMap<MemoryRegion, Arc<Mutex<BoxBytes>>>,
+}
+
+impl MemoryMonitor {
+    pub fn new(client: EmulatorClient) -> Self {
+        Self {
+            client,
+            regions: HashMap::new(),
+        }
+    }
+
+    pub fn view(&mut self, sim: SimId, start: u32, length: usize) -> MemoryView {
+        let region = MemoryRegion { sim, start, length };
+        let memory = self.regions.entry(region).or_insert_with(|| {
+            let mut buf = aligned_memory(start, length);
+            let (tx, rx) = oneshot::channel();
+            self.client
+                .send_command(EmulatorCommand::ReadMemory(sim, start, length, vec![], tx));
+            let bytes = pollster::block_on(rx).unwrap();
+            buf.copy_from_slice(&bytes);
+            #[expect(clippy::arc_with_non_send_sync)] // TODO: remove after bytemuck upgrade
+            Arc::new(Mutex::new(buf))
+        });
+        MemoryView {
+            memory: memory.clone(),
+        }
+    }
+}
+
+fn aligned_memory(start: u32, length: usize) -> BoxBytes {
+    if start % 4 == 0 && length % 4 == 0 {
+        let memory = vec![0u32; length / 4].into_boxed_slice();
+        return bytemuck::box_bytes_of(memory);
+    }
+    if start % 2 == 0 && length % 2 == 0 {
+        let memory = vec![0u16; length / 2].into_boxed_slice();
+        return bytemuck::box_bytes_of(memory);
+    }
+    let memory = vec![0u8; length].into_boxed_slice();
+    bytemuck::box_bytes_of(memory)
+}
+
+pub struct MemoryView {
+    memory: Arc<Mutex<BoxBytes>>,
+}
+// SAFETY: BoxBytes is supposed to be Send+Sync, will be in a new version
+unsafe impl Send for MemoryView {}
+
+impl MemoryView {
+    pub fn borrow(&self) -> MemoryRef<'_> {
+        MemoryRef {
+            inner: self.memory.lock().unwrap(),
+        }
+    }
+}
+
+pub struct MemoryRef<'a> {
+    inner: MutexGuard<'a, BoxBytes>,
+}
+
+impl MemoryRef<'_> {
+    pub fn read<T: bytemuck::AnyBitPattern>(&self, index: usize) -> T {
+        let from = index * size_of::<T>();
+        let to = from + size_of::<T>();
+        *bytemuck::from_bytes(&self.inner[from..to])
+    }
+
+    pub fn range<T: bytemuck::AnyBitPattern>(&self, start: usize, count: usize) -> &[T] {
+        let from = start * size_of::<T>();
+        let to = from + (count * size_of::<T>());
+        bytemuck::cast_slice(&self.inner[from..to])
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+struct MemoryRegion {
+    sim: SimId,
+    start: u32,
+    length: usize,
+}

src/vram.rs

@@ -0,0 +1,293 @@
+use std::{
+    collections::HashMap,
+    ops::Deref,
+    sync::{Arc, Mutex, Weak},
+    thread,
+    time::Duration,
+};
+
+use egui::{
+    epaint::ImageDelta,
+    load::{LoadError, SizedTexture, TextureLoader, TexturePoll},
+    Color32, ColorImage, TextureHandle, TextureOptions,
+};
+use tokio::{sync::mpsc, time::timeout};
+
+pub struct VramProcessor {
+    sender: mpsc::UnboundedSender<Box<dyn VramRendererImpl>>,
+}
+
+impl VramProcessor {
+    pub fn new() -> Self {
+        let (sender, receiver) = mpsc::unbounded_channel();
+        thread::spawn(move || {
+            tokio::runtime::Builder::new_current_thread()
+                .enable_all()
+                .build()
+                .unwrap()
+                .block_on(async move {
+                    let mut worker = VramProcessorWorker {
+                        receiver,
+                        renderers: vec![],
+                    };
+                    worker.run().await
+                })
+        });
+        Self { sender }
+    }
+
+    pub fn add<const N: usize, R: VramRenderer<N> + 'static>(
+        &self,
+        renderer: R,
+    ) -> ([VramImageHandle; N], VramParams<R::Params>) {
+        let handles = renderer.sizes().map(|[width, height]| {
+            let data = Arc::new(Mutex::new(None));
+            VramImageHandle {
+                size: [width as f32, height as f32],
+                data,
+            }
+        });
+        let images = renderer
+            .sizes()
+            .map(|[width, height]| VramImage::new(width, height));
+        let sink = Arc::new(Mutex::new(R::Params::default()));
+        let _ = self.sender.send(Box::new(VramRendererWrapper {
+            renderer,
+            params: Arc::downgrade(&sink),
+            images,
+            sinks: handles.clone().map(|i| i.data),
+        }));
+        let params = VramParams {
+            value: R::Params::default(),
+            sink,
+        };
+        (handles, params)
+    }
+}
+
+struct VramProcessorWorker {
+    receiver: mpsc::UnboundedReceiver<Box<dyn VramRendererImpl>>,
+    renderers: Vec<Box<dyn VramRendererImpl>>,
+}
+
+impl VramProcessorWorker {
+    async fn run(&mut self) {
+        loop {
+            if self.renderers.is_empty() {
+                // if we have nothing to do, block until we have something to do
+                if self.receiver.recv_many(&mut self.renderers, 64).await == 0 {
+                    // shutdown
+                    return;
+                }
+                while let Ok(renderer) = self.receiver.try_recv() {
+                    self.renderers.push(renderer);
+                }
+            }
+            self.renderers
+                .retain_mut(|renderer| renderer.try_update().is_ok());
+            // wait up to 10 ms for more renderers
+            if timeout(
+                Duration::from_millis(10),
+                self.receiver.recv_many(&mut self.renderers, 64),
+            )
+            .await
+            .is_ok()
+            {
+                while let Ok(renderer) = self.receiver.try_recv() {
+                    self.renderers.push(renderer);
+                }
+            }
+        }
+    }
+}
+
+pub enum VramImage {
+    Unchanged(Option<Arc<ColorImage>>),
+    Changed(ColorImage),
+}
+
+impl VramImage {
+    pub fn new(width: usize, height: usize) -> Self {
+        Self::Changed(ColorImage::new([width, height], Color32::BLACK))
+    }
+
+    pub fn write(&mut self, coords: (usize, usize), shade: u8) {
+        match self {
+            Self::Unchanged(image) => {
+                if image.as_ref().is_none_or(|i| i[coords].r() == shade) {
+                    return;
+                }
+                let Some(mut new_image) = image.take().map(Arc::unwrap_or_clone) else {
+                    return;
+                };
+                new_image[coords] = Color32::from_gray(shade);
+                *self = Self::Changed(new_image);
+            }
+            Self::Changed(image) => {
+                image[coords] = Color32::from_gray(shade);
+            }
+        }
+    }
+
+    pub fn take(&mut self) -> Option<Arc<ColorImage>> {
+        match self {
+            Self::Unchanged(_) => None,
+            Self::Changed(image) => {
+                let arced = Arc::new(std::mem::take(image));
+                *self = Self::Unchanged(Some(arced.clone()));
+                Some(arced)
+            }
+        }
+    }
+}
+
+#[derive(Clone)]
+pub struct VramImageHandle {
+    size: [f32; 2],
+    data: Arc<Mutex<Option<Arc<ColorImage>>>>,
+}
+
+impl VramImageHandle {
+    fn pull(&mut self) -> Option<Arc<ColorImage>> {
+        self.data.lock().unwrap().take()
+    }
+}
+
+pub struct VramParams<T> {
+    value: T,
+    sink: Arc<Mutex<T>>,
+}
+
+impl<T> Deref for VramParams<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.value
+    }
+}
+
+impl<T: Clone + Eq> VramParams<T> {
+    pub fn write(&mut self, value: T) {
+        if self.value != value {
+            self.value = value.clone();
+            *self.sink.lock().unwrap() = value;
+        }
+    }
+}
+
+pub trait VramRenderer<const N: usize>: Send {
+    type Params: Clone + Default + Send;
+    fn sizes(&self) -> [[usize; 2]; N];
+    fn render(&mut self, params: &Self::Params, images: &mut [VramImage; N]);
+}
+
+struct VramRendererWrapper<const N: usize, R: VramRenderer<N>> {
+    renderer: R,
+    params: Weak<Mutex<R::Params>>,
+    images: [VramImage; N],
+    sinks: [Arc<Mutex<Option<Arc<ColorImage>>>>; N],
+}
+
+trait VramRendererImpl: Send {
+    fn try_update(&mut self) -> Result<(), ()>;
+}
+
+impl<const N: usize, R: VramRenderer<N> + Send> VramRendererImpl for VramRendererWrapper<N, R> {
+    fn try_update(&mut self) -> Result<(), ()> {
+        let params = match self.params.upgrade() {
+            Some(params) => params.lock().unwrap().clone(),
+            None => {
+                // the UI isn't using this anymore
+                return Err(());
+            }
+        };
+        self.renderer.render(&params, &mut self.images);
+
+        for (image, sink) in self.images.iter_mut().zip(&self.sinks) {
+            if let Some(update) = image.take() {
+                sink.lock().unwrap().replace(update);
+            }
+        }
+        Ok(())
+    }
+}
+
+pub struct VramTextureLoader {
+    cache: Mutex<HashMap<String, (VramImageHandle, Option<TextureHandle>)>>,
+}
+
+impl VramTextureLoader {
+    pub fn new(renderers: impl IntoIterator<Item = (String, VramImageHandle)>) -> Self {
+        let mut cache = HashMap::new();
+        for (key, image) in renderers {
+            cache.insert(key, (image, None));
+        }
+        Self {
+            cache: Mutex::new(cache),
+        }
+    }
+}
+
+impl TextureLoader for VramTextureLoader {
+    fn id(&self) -> &str {
+        concat!(module_path!(), "VramTextureLoader")
+    }
+
+    fn load(
+        &self,
+        ctx: &egui::Context,
+        uri: &str,
+        texture_options: TextureOptions,
+        _size_hint: egui::SizeHint,
+    ) -> Result<TexturePoll, LoadError> {
+        let mut cache = self.cache.lock().unwrap();
+        let Some((image, maybe_handle)) = cache.get_mut(uri) else {
+            return Err(LoadError::NotSupported);
+        };
+        if texture_options != TextureOptions::NEAREST {
+            return Err(LoadError::Loading(
+                "Only TextureOptions::NEAREST are supported".into(),
+            ));
+        }
+        match (image.pull(), maybe_handle.as_ref()) {
+            (Some(update), Some(handle)) => {
+                let delta = ImageDelta::full(update, texture_options);
+                ctx.tex_manager().write().set(handle.id(), delta);
+                let texture = SizedTexture::new(handle, image.size);
+                Ok(TexturePoll::Ready { texture })
+            }
+            (Some(update), None) => {
+                let handle = ctx.load_texture(uri, update, texture_options);
+                let texture = SizedTexture::new(&handle, image.size);
+                maybe_handle.replace(handle);
+                Ok(TexturePoll::Ready { texture })
+            }
+            (None, Some(handle)) => {
+                let texture = SizedTexture::new(handle, image.size);
+                Ok(TexturePoll::Ready { texture })
+            }
+            (None, None) => {
+                let size = image.size.into();
+                Ok(TexturePoll::Pending { size: Some(size) })
+            }
+        }
+    }
+
+    fn forget(&self, uri: &str) {
+        let _ = uri;
+    }
+
+    fn forget_all(&self) {}
+
+    fn byte_size(&self) -> usize {
+        self.cache
+            .lock()
+            .unwrap()
+            .values()
+            .map(|(image, _)| {
+                let [width, height] = image.size;
+                width as usize * height as usize * 4
+            })
+            .sum()
+    }
+}

src/window.rs

@@ -3,6 +3,7 @@ use egui::{Context, ViewportBuilder, ViewportId};
 pub use game::GameWindow;
 pub use gdb::GdbServerWindow;
 pub use input::InputWindow;
+pub use vram::{BgMapWindow, CharacterDataWindow};
 use winit::event::KeyEvent;
 
 use crate::emulator::SimId;
@@ -12,6 +13,8 @@ mod game;
 mod game_screen;
 mod gdb;
 mod input;
+mod utils;
+mod vram;
 
 pub trait AppWindow {
     fn viewport_id(&self) -> ViewportId;
@@ -20,7 +23,8 @@ pub trait AppWindow {
     }
     fn initial_viewport(&self) -> ViewportBuilder;
     fn show(&mut self, ctx: &Context);
-    fn on_init(&mut self, render_state: &egui_wgpu::RenderState) {
+    fn on_init(&mut self, ctx: &Context, render_state: &egui_wgpu::RenderState) {
+        let _ = ctx;
         let _ = render_state;
     }
     fn on_destroy(&mut self) {}

src/window/game.rs

@@ -6,9 +6,8 @@ use crate::{
     persistence::Persistence,
 };
 use egui::{
-    ecolor::HexColor, menu, Align2, Button, CentralPanel, Color32, Context, Direction, Frame,
-    Layout, Response, Sense, TopBottomPanel, Ui, Vec2, ViewportBuilder, ViewportCommand,
-    ViewportId, WidgetText, Window,
+    menu, Align2, Button, CentralPanel, Color32, Context, Direction, Frame, TopBottomPanel, Ui,
+    Vec2, ViewportBuilder, ViewportCommand, ViewportId, Window,
 };
 use egui_toast::{Toast, Toasts};
 use serde::{Deserialize, Serialize};
@@ -16,6 +15,7 @@ use winit::event_loop::EventLoopProxy;
 
 use super::{
     game_screen::{DisplayMode, GameScreen},
+    utils::UiExt as _,
     AppWindow,
 };
 
@@ -132,6 +132,18 @@ impl GameWindow {
                     .unwrap();
                 ui.close_menu();
             }
+            if ui.button("Character Data").clicked() {
+                self.proxy
+                    .send_event(UserEvent::OpenCharacterData(self.sim_id))
+                    .unwrap();
+                ui.close_menu();
+            }
+            if ui.button("Background Maps").clicked() {
+                self.proxy
+                    .send_event(UserEvent::OpenBgMap(self.sim_id))
+                    .unwrap();
+                ui.close_menu();
+            }
         });
         ui.menu_button("About", |ui| {
             self.proxy.send_event(UserEvent::OpenAbout).unwrap();
@@ -369,7 +381,7 @@ impl AppWindow for GameWindow {
         toasts.show(ctx);
     }
 
-    fn on_init(&mut self, render_state: &egui_wgpu::RenderState) {
+    fn on_init(&mut self, _ctx: &Context, render_state: &egui_wgpu::RenderState) {
         let (screen, sink) = GameScreen::init(render_state);
         let (message_sink, message_source) = mpsc::channel();
         self.client.send_command(EmulatorCommand::ConnectToSim(
@@ -389,69 +401,6 @@ impl AppWindow for GameWindow {
     }
 }
 
-trait UiExt {
-    fn selectable_button(&mut self, selected: bool, text: impl Into<WidgetText>) -> Response;
-    fn selectable_option<T: Eq>(
-        &mut self,
-        current_value: &mut T,
-        selected_value: T,
-        text: impl Into<WidgetText>,
-    ) -> Response {
-        let response = self.selectable_button(*current_value == selected_value, text);
-        if response.clicked() {
-            *current_value = selected_value;
-        }
-        response
-    }
-
-    fn color_pair_button(&mut self, left: Color32, right: Color32) -> Response;
-
-    fn color_picker(&mut self, color: &mut Color32, hex: &mut String) -> Response;
-}
-
-impl UiExt for Ui {
-    fn selectable_button(&mut self, selected: bool, text: impl Into<WidgetText>) -> Response {
-        self.style_mut().visuals.widgets.inactive.bg_fill = Color32::TRANSPARENT;
-        self.style_mut().visuals.widgets.hovered.bg_fill = Color32::TRANSPARENT;
-        self.style_mut().visuals.widgets.active.bg_fill = Color32::TRANSPARENT;
-        let mut selected = selected;
-        self.checkbox(&mut selected, text)
-    }
-
-    fn color_pair_button(&mut self, left: Color32, right: Color32) -> Response {
-        let button_size = Vec2::new(60.0, 20.0);
-        let (rect, response) = self.allocate_at_least(button_size, Sense::click());
-        let center_x = rect.center().x;
-        let left_rect = rect.with_max_x(center_x);
-        self.painter().rect_filled(left_rect, 0.0, left);
-        let right_rect = rect.with_min_x(center_x);
-        self.painter().rect_filled(right_rect, 0.0, right);
-
-        let style = self.style().interact(&response);
-        self.painter().rect_stroke(rect, 0.0, style.fg_stroke);
-        response
-    }
-
-    fn color_picker(&mut self, color: &mut Color32, hex: &mut String) -> Response {
-        self.allocate_ui_with_layout(
-            Vec2::new(100.0, 130.0),
-            Layout::top_down_justified(egui::Align::Center),
-            |ui| {
-                let (rect, _) = ui.allocate_at_least(Vec2::new(100.0, 100.0), Sense::hover());
-                ui.painter().rect_filled(rect, 0.0, *color);
-                let resp = ui.text_edit_singleline(hex);
-                if resp.changed() {
-                    if let Ok(new_color) = HexColor::from_str_without_hash(hex) {
-                        *color = new_color.color();
-                    }
-                }
-                resp
-            },
-        )
-        .inner
-    }
-}
-
 struct ColorPickerState {
     color_codes: [String; 2],
     just_opened: bool,

src/window/utils.rs

@@ -0,0 +1,107 @@
+use std::{ops::Range, str::FromStr};
+
+use egui::{
+    ecolor::HexColor, Align, Color32, Frame, Layout, Response, RichText, Sense, TextEdit, Ui,
+    UiBuilder, Vec2, WidgetText,
+};
+
+pub trait UiExt {
+    fn section(&mut self, title: impl Into<String>, add_contents: impl FnOnce(&mut Ui));
+    fn selectable_button(&mut self, selected: bool, text: impl Into<WidgetText>) -> Response;
+    fn selectable_option<T: Eq>(
+        &mut self,
+        current_value: &mut T,
+        selected_value: T,
+        text: impl Into<WidgetText>,
+    ) -> Response {
+        let response = self.selectable_button(*current_value == selected_value, text);
+        if response.clicked() {
+            *current_value = selected_value;
+        }
+        response
+    }
+
+    fn color_pair_button(&mut self, left: Color32, right: Color32) -> Response;
+
+    fn color_picker(&mut self, color: &mut Color32, hex: &mut String) -> Response;
+
+    fn number_picker<T: FromStr + PartialOrd>(
+        &mut self,
+        text: &mut String,
+        value: &mut T,
+        range: Range<T>,
+    );
+}
+
+impl UiExt for Ui {
+    fn section(&mut self, title: impl Into<String>, add_contents: impl FnOnce(&mut Ui)) {
+        let mut frame = Frame::group(self.style());
+        frame.outer_margin.top += 10.0;
+        frame.inner_margin.top += 2.0;
+        let res = frame.show(self, add_contents);
+        let text = RichText::new(title).background_color(self.style().visuals.panel_fill);
+        let old_rect = res.response.rect;
+        let mut text_rect = old_rect;
+        text_rect.min.x += 6.0;
+        let new_rect = self
+            .allocate_new_ui(UiBuilder::new().max_rect(text_rect), |ui| ui.label(text))
+            .response
+            .rect;
+        self.allocate_space((old_rect.max - new_rect.max) - (old_rect.min - new_rect.min));
+    }
+
+    fn selectable_button(&mut self, selected: bool, text: impl Into<WidgetText>) -> Response {
+        self.style_mut().visuals.widgets.inactive.bg_fill = Color32::TRANSPARENT;
+        self.style_mut().visuals.widgets.hovered.bg_fill = Color32::TRANSPARENT;
+        self.style_mut().visuals.widgets.active.bg_fill = Color32::TRANSPARENT;
+        let mut selected = selected;
+        self.checkbox(&mut selected, text)
+    }
+
+    fn color_pair_button(&mut self, left: Color32, right: Color32) -> Response {
+        let button_size = Vec2::new(60.0, 20.0);
+        let (rect, response) = self.allocate_at_least(button_size, Sense::click());
+        let center_x = rect.center().x;
+        let left_rect = rect.with_max_x(center_x);
+        self.painter().rect_filled(left_rect, 0.0, left);
+        let right_rect = rect.with_min_x(center_x);
+        self.painter().rect_filled(right_rect, 0.0, right);
+
+        let style = self.style().interact(&response);
+        self.painter().rect_stroke(rect, 0.0, style.fg_stroke);
+        response
+    }
+
+    fn color_picker(&mut self, color: &mut Color32, hex: &mut String) -> Response {
+        self.allocate_ui_with_layout(
+            Vec2::new(100.0, 130.0),
+            Layout::top_down_justified(egui::Align::Center),
+            |ui| {
+                let (rect, _) = ui.allocate_at_least(Vec2::new(100.0, 100.0), Sense::hover());
+                ui.painter().rect_filled(rect, 0.0, *color);
+                let resp = ui.text_edit_singleline(hex);
+                if resp.changed() {
+                    if let Ok(new_color) = HexColor::from_str_without_hash(hex) {
+                        *color = new_color.color();
+                    }
+                }
+                resp
+            },
+        )
+        .inner
+    }
+
+    fn number_picker<T: FromStr + PartialOrd>(
+        &mut self,
+        text: &mut String,
+        value: &mut T,
+        range: Range<T>,
+    ) {
+        let res = self.add(TextEdit::singleline(text).horizontal_align(Align::Max));
+        if res.changed() {
+            if let Some(new_value) = text.parse().ok().filter(|v| range.contains(v)) {
+                *value = new_value;
+            }
+        }
+    }
+}

src/window/vram.rs

@@ -0,0 +1,6 @@
+mod bgmap;
+mod chardata;
+mod utils;
+
+pub use bgmap::*;
+pub use chardata::*;

src/window/vram/bgmap.rs

@@ -0,0 +1,342 @@
+use std::sync::Arc;
+
+use egui::{
+    Align, CentralPanel, Checkbox, Color32, Context, Image, ScrollArea, Slider, TextEdit,
+    TextureOptions, Ui, ViewportBuilder, ViewportId,
+};
+use egui_extras::{Column, Size, StripBuilder, TableBuilder};
+
+use crate::{
+    emulator::SimId,
+    memory::{MemoryMonitor, MemoryView},
+    vram::{VramImage, VramParams, VramProcessor, VramRenderer, VramTextureLoader},
+    window::{utils::UiExt, AppWindow},
+};
+
+use super::utils::{parse_palette, CharacterGrid, GENERIC_PALETTE};
+
+pub struct BgMapWindow {
+    sim_id: SimId,
+    loader: Arc<VramTextureLoader>,
+    bgmaps: MemoryView,
+    cell_index: usize,
+    cell_index_str: String,
+    generic_palette: bool,
+    params: VramParams<BgMapParams>,
+    scale: f32,
+    show_grid: bool,
+}
+
+impl BgMapWindow {
+    pub fn new(sim_id: SimId, memory: &mut MemoryMonitor, vram: &mut VramProcessor) -> Self {
+        let renderer = BgMapRenderer::new(sim_id, memory);
+        let ([cell, bgmap], params) = vram.add(renderer);
+        let loader =
+            VramTextureLoader::new([("vram://cell".into(), cell), ("vram://bgmap".into(), bgmap)]);
+        Self {
+            sim_id,
+            loader: Arc::new(loader),
+            bgmaps: memory.view(sim_id, 0x00020000, 0x1d800),
+            cell_index: 0,
+            cell_index_str: "0".into(),
+            generic_palette: false,
+            params,
+            scale: 1.0,
+            show_grid: false,
+        }
+    }
+
+    fn show_form(&mut self, ui: &mut Ui) {
+        let row_height = ui.spacing().interact_size.y;
+        ui.vertical(|ui| {
+            TableBuilder::new(ui)
+                .column(Column::auto())
+                .column(Column::remainder())
+                .body(|mut body| {
+                    body.row(row_height, |mut row| {
+                        row.col(|ui| {
+                            ui.label("Map");
+                        });
+                        row.col(|ui| {
+                            let mut bgmap_index = self.cell_index / 4096;
+                            let mut bgmap_index_str = bgmap_index.to_string();
+                            ui.number_picker(&mut bgmap_index_str, &mut bgmap_index, 0..14);
+                            if bgmap_index != self.cell_index / 4096 {
+                                self.cell_index = (bgmap_index * 4096) + (self.cell_index % 4096);
+                                self.cell_index_str = self.cell_index.to_string();
+                            }
+                        });
+                    });
+                    body.row(row_height, |mut row| {
+                        row.col(|ui| {
+                            ui.label("Cell");
+                        });
+                        row.col(|ui| {
+                            ui.number_picker(
+                                &mut self.cell_index_str,
+                                &mut self.cell_index,
+                                0..16 * 4096,
+                            );
+                        });
+                    });
+                    body.row(row_height, |mut row| {
+                        row.col(|ui| {
+                            ui.label("Address");
+                        });
+                        row.col(|ui| {
+                            let address = 0x00020000 + (self.cell_index * 2);
+                            let mut address_str = format!("{address:08x}");
+                            ui.add_enabled(
+                                false,
+                                TextEdit::singleline(&mut address_str).horizontal_align(Align::Max),
+                            );
+                        });
+                    });
+                });
+            let image = Image::new("vram://cell")
+                .maintain_aspect_ratio(true)
+                .tint(Color32::RED)
+                .texture_options(TextureOptions::NEAREST);
+            ui.add(image);
+            ui.section("Cell", |ui| {
+                let cell = self.bgmaps.borrow().read::<u16>(self.cell_index);
+                let (char_index, mut vflip, mut hflip, palette_index) = parse_cell(cell);
+                TableBuilder::new(ui)
+                    .column(Column::remainder())
+                    .column(Column::remainder())
+                    .body(|mut body| {
+                        body.row(row_height, |mut row| {
+                            row.col(|ui| {
+                                ui.label("Character");
+                            });
+                            row.col(|ui| {
+                                let mut character_str = char_index.to_string();
+                                ui.add_enabled(
+                                    false,
+                                    TextEdit::singleline(&mut character_str)
+                                        .horizontal_align(Align::Max),
+                                );
+                            });
+                        });
+                        body.row(row_height, |mut row| {
+                            row.col(|ui| {
+                                ui.label("Palette");
+                            });
+                            row.col(|ui| {
+                                let mut palette = format!("BG {}", palette_index);
+                                ui.add_enabled(
+                                    false,
+                                    TextEdit::singleline(&mut palette).horizontal_align(Align::Max),
+                                );
+                            });
+                        });
+                        body.row(row_height, |mut row| {
+                            row.col(|ui| {
+                                let checkbox = Checkbox::new(&mut hflip, "H-flip");
+                                ui.add_enabled(false, checkbox);
+                            });
+                            row.col(|ui| {
+                                let checkbox = Checkbox::new(&mut vflip, "V-flip");
+                                ui.add_enabled(false, checkbox);
+                            });
+                        });
+                    });
+                ui.section("Display", |ui| {
+                    ui.horizontal(|ui| {
+                        ui.label("Scale");
+                        ui.spacing_mut().slider_width = ui.available_width();
+                        let slider = Slider::new(&mut self.scale, 1.0..=10.0)
+                            .step_by(1.0)
+                            .show_value(false);
+                        ui.add(slider);
+                    });
+                    ui.checkbox(&mut self.show_grid, "Show grid");
+                    ui.checkbox(&mut self.generic_palette, "Generic palette");
+                });
+            });
+        });
+        self.params.write(BgMapParams {
+            cell_index: self.cell_index,
+            generic_palette: self.generic_palette,
+        });
+    }
+
+    fn show_bgmap(&mut self, ui: &mut Ui) {
+        let grid = CharacterGrid::new("vram://bgmap")
+            .with_scale(self.scale)
+            .with_grid(self.show_grid)
+            .with_selected(self.cell_index % 4096);
+        if let Some(selected) = grid.show(ui) {
+            self.cell_index = (self.cell_index / 4096 * 4096) + selected;
+            self.cell_index_str = self.cell_index.to_string();
+        }
+    }
+}
+
+impl AppWindow for BgMapWindow {
+    fn viewport_id(&self) -> ViewportId {
+        ViewportId::from_hash_of(format!("bgmap-{}", self.sim_id))
+    }
+
+    fn sim_id(&self) -> SimId {
+        self.sim_id
+    }
+
+    fn initial_viewport(&self) -> ViewportBuilder {
+        ViewportBuilder::default()
+            .with_title(format!("BG Map Data ({})", self.sim_id))
+            .with_inner_size((640.0, 480.0))
+    }
+
+    fn on_init(&mut self, ctx: &Context, _render_state: &egui_wgpu::RenderState) {
+        ctx.add_texture_loader(self.loader.clone());
+    }
+
+    fn show(&mut self, ctx: &Context) {
+        CentralPanel::default().show(ctx, |ui| {
+            ui.horizontal_top(|ui| {
+                StripBuilder::new(ui)
+                    .size(Size::relative(0.3))
+                    .size(Size::remainder())
+                    .horizontal(|mut strip| {
+                        strip.cell(|ui| {
+                            ScrollArea::vertical().show(ui, |ui| self.show_form(ui));
+                        });
+                        strip.cell(|ui| {
+                            ScrollArea::both().show(ui, |ui| self.show_bgmap(ui));
+                        });
+                    })
+            });
+        });
+    }
+}
+
+fn parse_cell(cell: u16) -> (usize, bool, bool, usize) {
+    let char_index = (cell & 0x7ff) as usize;
+    let vflip = cell & 0x1000 != 0;
+    let hflip = cell & 0x2000 != 0;
+    let palette_index = (cell >> 14) as usize;
+    (char_index, vflip, hflip, palette_index)
+}
+
+#[derive(Default, Clone, PartialEq, Eq)]
+struct BgMapParams {
+    cell_index: usize,
+    generic_palette: bool,
+}
+
+struct BgMapRenderer {
+    chardata: MemoryView,
+    bgmaps: MemoryView,
+    brightness: MemoryView,
+    palettes: MemoryView,
+}
+
+impl BgMapRenderer {
+    pub fn new(sim_id: SimId, memory: &mut MemoryMonitor) -> Self {
+        Self {
+            chardata: memory.view(sim_id, 0x00078000, 0x8000),
+            bgmaps: memory.view(sim_id, 0x00020000, 0x1d800),
+            brightness: memory.view(sim_id, 0x0005f824, 8),
+            palettes: memory.view(sim_id, 0x0005f860, 16),
+        }
+    }
+
+    fn render_bgmap(&self, image: &mut VramImage, bgmap_index: usize, generic_palette: bool) {
+        let chardata = self.chardata.borrow();
+        let bgmaps = self.bgmaps.borrow();
+        let brightness = self.brightness.borrow();
+        let palettes = self.palettes.borrow();
+
+        let brts = brightness.range::<u8>(0, 8);
+        let colors = if generic_palette {
+            [
+                GENERIC_PALETTE,
+                GENERIC_PALETTE,
+                GENERIC_PALETTE,
+                GENERIC_PALETTE,
+            ]
+        } else {
+            [
+                parse_palette(palettes.read(0), brts),
+                parse_palette(palettes.read(2), brts),
+                parse_palette(palettes.read(4), brts),
+                parse_palette(palettes.read(6), brts),
+            ]
+        };
+
+        for (i, cell) in bgmaps
+            .range::<u16>(bgmap_index * 4096, 4096)
+            .iter()
+            .enumerate()
+        {
+            let (char_index, vflip, hflip, palette_index) = parse_cell(*cell);
+            let char = chardata.range::<u16>(char_index * 8, 8);
+            let palette = &colors[palette_index];
+
+            for row in 0..8 {
+                let y = row + (i / 64) * 8;
+                for (col, pixel) in self.read_char_row(char, hflip, vflip, row).enumerate() {
+                    let x = col + (i % 64) * 8;
+                    image.write((x, y), palette[pixel as usize]);
+                }
+            }
+        }
+    }
+
+    fn render_bgmap_cell(&self, image: &mut VramImage, index: usize, generic_palette: bool) {
+        let chardata = self.chardata.borrow();
+        let bgmaps = self.bgmaps.borrow();
+        let brightness = self.brightness.borrow();
+        let palettes = self.palettes.borrow();
+
+        let brts = brightness.range::<u8>(0, 8);
+
+        let cell = bgmaps.read::<u16>(index);
+
+        let (char_index, vflip, hflip, palette_index) = parse_cell(cell);
+        let char = chardata.range::<u16>(char_index * 8, 8);
+        let palette = if generic_palette {
+            GENERIC_PALETTE
+        } else {
+            parse_palette(palettes.read(palette_index * 2), brts)
+        };
+
+        for row in 0..8 {
+            for (col, pixel) in self.read_char_row(char, hflip, vflip, row).enumerate() {
+                image.write((col, row), palette[pixel as usize]);
+            }
+        }
+    }
+
+    fn read_char_row(
+        &self,
+        char: &[u16],
+        hflip: bool,
+        vflip: bool,
+        row: usize,
+    ) -> impl Iterator<Item = u8> {
+        let pixels = if vflip { char[7 - row] } else { char[row] };
+        (0..16).step_by(2).map(move |i| {
+            let pixel = if hflip { 14 - i } else { i };
+            ((pixels >> pixel) & 0x3) as u8
+        })
+    }
+}
+
+impl VramRenderer<2> for BgMapRenderer {
+    type Params = BgMapParams;
+
+    fn sizes(&self) -> [[usize; 2]; 2] {
+        [[8, 8], [8 * 64, 8 * 64]]
+    }
+
+    fn render(&mut self, params: &Self::Params, images: &mut [VramImage; 2]) {
+        self.render_bgmap_cell(&mut images[0], params.cell_index, params.generic_palette);
+        self.render_bgmap(
+            &mut images[1],
+            params.cell_index / 4096,
+            params.generic_palette,
+        );
+    }
+}

src/window/vram/chardata.rs

@@ -0,0 +1,458 @@
+use std::{fmt::Display, sync::Arc};
+
+use egui::{
+    Align, CentralPanel, Color32, ComboBox, Context, Image, ScrollArea, Slider, TextEdit,
+    TextureOptions, Ui, Vec2, ViewportBuilder, ViewportId,
+};
+use egui_extras::{Column, Size, StripBuilder, TableBuilder};
+use serde::{Deserialize, Serialize};
+
+use crate::{
+    emulator::SimId,
+    memory::{MemoryMonitor, MemoryView},
+    vram::{VramImage, VramParams, VramProcessor, VramRenderer, VramTextureLoader},
+    window::{utils::UiExt as _, AppWindow},
+};
+
+use super::utils::{self, CharacterGrid};
+
+#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum VramPalette {
+    #[default]
+    Generic,
+    Bg0,
+    Bg1,
+    Bg2,
+    Bg3,
+    Obj0,
+    Obj1,
+    Obj2,
+    Obj3,
+}
+
+impl VramPalette {
+    pub const fn values() -> [VramPalette; 9] {
+        [
+            Self::Generic,
+            Self::Bg0,
+            Self::Bg1,
+            Self::Bg2,
+            Self::Bg3,
+            Self::Obj0,
+            Self::Obj1,
+            Self::Obj2,
+            Self::Obj3,
+        ]
+    }
+
+    pub const fn offset(self) -> Option<usize> {
+        match self {
+            Self::Generic => None,
+            Self::Bg0 => Some(0),
+            Self::Bg1 => Some(2),
+            Self::Bg2 => Some(4),
+            Self::Bg3 => Some(6),
+            Self::Obj0 => Some(8),
+            Self::Obj1 => Some(10),
+            Self::Obj2 => Some(12),
+            Self::Obj3 => Some(14),
+        }
+    }
+}
+
+impl Display for VramPalette {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Generic => f.write_str("Generic"),
+            Self::Bg0 => f.write_str("BG 0"),
+            Self::Bg1 => f.write_str("BG 1"),
+            Self::Bg2 => f.write_str("BG 2"),
+            Self::Bg3 => f.write_str("BG 3"),
+            Self::Obj0 => f.write_str("OBJ 0"),
+            Self::Obj1 => f.write_str("OBJ 1"),
+            Self::Obj2 => f.write_str("OBJ 2"),
+            Self::Obj3 => f.write_str("OBJ 3"),
+        }
+    }
+}
+
+pub struct CharacterDataWindow {
+    sim_id: SimId,
+    loader: Arc<VramTextureLoader>,
+    brightness: MemoryView,
+    palettes: MemoryView,
+    palette: VramPalette,
+    index: usize,
+    index_str: String,
+    params: VramParams<CharDataParams>,
+    scale: f32,
+    show_grid: bool,
+}
+
+impl CharacterDataWindow {
+    pub fn new(sim_id: SimId, memory: &mut MemoryMonitor, vram: &mut VramProcessor) -> Self {
+        let renderer = CharDataRenderer::new(sim_id, memory);
+        let ([char, chardata], params) = vram.add(renderer);
+        let loader = VramTextureLoader::new([
+            ("vram://char".into(), char),
+            ("vram://chardata".into(), chardata),
+        ]);
+        Self {
+            sim_id,
+            loader: Arc::new(loader),
+            brightness: memory.view(sim_id, 0x0005f824, 8),
+            palettes: memory.view(sim_id, 0x0005f860, 16),
+            palette: params.palette,
+            index: params.index,
+            index_str: params.index.to_string(),
+            params,
+            scale: 4.0,
+            show_grid: true,
+        }
+    }
+
+    fn show_form(&mut self, ui: &mut Ui) {
+        let row_height = ui.spacing().interact_size.y;
+        ui.vertical(|ui| {
+            TableBuilder::new(ui)
+                .column(Column::auto())
+                .column(Column::remainder())
+                .body(|mut body| {
+                    body.row(row_height, |mut row| {
+                        row.col(|ui| {
+                            ui.label("Index");
+                        });
+                        row.col(|ui| {
+                            ui.number_picker(&mut self.index_str, &mut self.index, 0..2048);
+                        });
+                    });
+                    body.row(row_height, |mut row| {
+                        row.col(|ui| {
+                            ui.label("Address");
+                        });
+                        row.col(|ui| {
+                            let address = match self.index {
+                                0x000..0x200 => 0x00060000 + self.index * 16,
+                                0x200..0x400 => 0x000e0000 + (self.index - 0x200) * 16,
+                                0x400..0x600 => 0x00160000 + (self.index - 0x400) * 16,
+                                0x600..0x800 => 0x001e0000 + (self.index - 0x600) * 16,
+                                _ => unreachable!("can't happen"),
+                            };
+                            let mut address_str = format!("{address:08x}");
+                            ui.add_enabled(
+                                false,
+                                TextEdit::singleline(&mut address_str).horizontal_align(Align::Max),
+                            );
+                        });
+                    });
+                    body.row(row_height, |mut row| {
+                        row.col(|ui| {
+                            ui.label("Mirror");
+                        });
+                        row.col(|ui| {
+                            let mirror = 0x00078000 + (self.index * 16);
+                            let mut mirror_str = format!("{mirror:08x}");
+                            ui.add_enabled(
+                                false,
+                                TextEdit::singleline(&mut mirror_str).horizontal_align(Align::Max),
+                            );
+                        });
+                    });
+                });
+            let image = Image::new("vram://char")
+                .maintain_aspect_ratio(true)
+                .tint(Color32::RED)
+                .texture_options(TextureOptions::NEAREST);
+            ui.add(image);
+            ui.section("Colors", |ui| {
+                ui.horizontal(|ui| {
+                    ui.label("Palette");
+                    ComboBox::from_id_salt("palette")
+                        .selected_text(self.palette.to_string())
+                        .width(ui.available_width())
+                        .show_ui(ui, |ui| {
+                            for palette in VramPalette::values() {
+                                ui.selectable_value(
+                                    &mut self.palette,
+                                    palette,
+                                    palette.to_string(),
+                                );
+                            }
+                        });
+                });
+                TableBuilder::new(ui)
+                    .columns(Column::remainder(), 4)
+                    .body(|mut body| {
+                        let palette = self.load_palette_colors();
+                        body.row(30.0, |mut row| {
+                            for color in palette {
+                                row.col(|ui| {
+                                    let rect = ui.available_rect_before_wrap();
+                                    let scale = rect.height() / rect.width();
+                                    let rect = rect.scale_from_center2(Vec2::new(scale, 1.0));
+                                    ui.painter().rect_filled(
+                                        rect,
+                                        0.0,
+                                        Color32::RED * Color32::from_gray(color),
+                                    );
+                                });
+                            }
+                        });
+                    });
+            });
+            ui.section("Display", |ui| {
+                ui.horizontal(|ui| {
+                    ui.label("Scale");
+                    ui.spacing_mut().slider_width = ui.available_width();
+                    let slider = Slider::new(&mut self.scale, 1.0..=10.0)
+                        .step_by(1.0)
+                        .show_value(false);
+                    ui.add(slider);
+                });
+                ui.checkbox(&mut self.show_grid, "Show grid");
+            });
+        });
+
+        self.params.write(CharDataParams {
+            palette: self.palette,
+            index: self.index,
+        });
+    }
+
+    fn load_palette_colors(&self) -> [u8; 4] {
+        let Some(offset) = self.palette.offset() else {
+            return utils::GENERIC_PALETTE;
+        };
+        let palette = self.palettes.borrow().read(offset);
+        let brightnesses = self.brightness.borrow();
+        let brts = brightnesses.range(0, 8);
+        utils::parse_palette(palette, brts)
+    }
+
+    fn show_chardata(&mut self, ui: &mut Ui) {
+        let grid = CharacterGrid::new("vram://chardata")
+            .with_scale(self.scale)
+            .with_grid(self.show_grid)
+            .with_selected(self.index);
+        if let Some(selected) = grid.show(ui) {
+            self.index = selected;
+            self.index_str = selected.to_string();
+        }
+    }
+}
+
+impl AppWindow for CharacterDataWindow {
+    fn viewport_id(&self) -> ViewportId {
+        ViewportId::from_hash_of(format!("chardata-{}", self.sim_id))
+    }
+
+    fn sim_id(&self) -> SimId {
+        self.sim_id
+    }
+
+    fn initial_viewport(&self) -> ViewportBuilder {
+        ViewportBuilder::default()
+            .with_title(format!("Character Data ({})", self.sim_id))
+            .with_inner_size((640.0, 480.0))
+    }
+
+    fn on_init(&mut self, ctx: &Context, _render_state: &egui_wgpu::RenderState) {
+        ctx.add_texture_loader(self.loader.clone());
+    }
+
+    fn show(&mut self, ctx: &Context) {
+        CentralPanel::default().show(ctx, |ui| {
+            ui.horizontal_top(|ui| {
+                StripBuilder::new(ui)
+                    .size(Size::relative(0.3))
+                    .size(Size::remainder())
+                    .horizontal(|mut strip| {
+                        strip.cell(|ui| {
+                            ScrollArea::vertical().show(ui, |ui| self.show_form(ui));
+                        });
+                        strip.cell(|ui| {
+                            ScrollArea::both().show(ui, |ui| self.show_chardata(ui));
+                        });
+                    });
+            });
+        });
+    }
+}
+
+#[derive(Serialize, Deserialize, Clone, PartialEq, Eq, Hash)]
+enum CharDataResource {
+    Character { palette: VramPalette, index: usize },
+    CharacterData { palette: VramPalette },
+}
+
+#[derive(Clone, Default, PartialEq, Eq)]
+struct CharDataParams {
+    palette: VramPalette,
+    index: usize,
+}
+
+struct CharDataRenderer {
+    chardata: MemoryView,
+    brightness: MemoryView,
+    palettes: MemoryView,
+}
+
+impl VramRenderer<2> for CharDataRenderer {
+    type Params = CharDataParams;
+
+    fn sizes(&self) -> [[usize; 2]; 2] {
+        [[8, 8], [16 * 8, 128 * 8]]
+    }
+
+    fn render(&mut self, params: &Self::Params, image: &mut [VramImage; 2]) {
+        self.render_character(&mut image[0], params.palette, params.index);
+        self.render_character_data(&mut image[1], params.palette);
+    }
+}
+
+impl CharDataRenderer {
+    pub fn new(sim_id: SimId, memory: &mut MemoryMonitor) -> Self {
+        Self {
+            chardata: memory.view(sim_id, 0x00078000, 0x8000),
+            brightness: memory.view(sim_id, 0x0005f824, 8),
+            palettes: memory.view(sim_id, 0x0005f860, 16),
+        }
+    }
+
+    fn render_character(&self, image: &mut VramImage, palette: VramPalette, index: usize) {
+        if index >= 2048 {
+            return;
+        }
+        let palette = self.load_palette(palette);
+        let chardata = self.chardata.borrow();
+        let character = chardata.range::<u16>(index * 8, 8);
+        for (row, pixels) in character.iter().enumerate() {
+            for col in 0..8 {
+                let char = (pixels >> (col * 2)) & 0x03;
+                image.write((col, row), palette[char as usize]);
+            }
+        }
+    }
+
+    fn render_character_data(&self, image: &mut VramImage, palette: VramPalette) {
+        let palette = self.load_palette(palette);
+        let chardata = self.chardata.borrow();
+        for (row, pixels) in chardata.range::<u16>(0, 8 * 2048).iter().enumerate() {
+            let char_index = row / 8;
+            let row_index = row % 8;
+            let x = (char_index % 16) * 8;
+            let y = (char_index / 16) * 8 + row_index;
+            for col in 0..8 {
+                let char = (pixels >> (col * 2)) & 0x03;
+                image.write((x + col, y), palette[char as usize]);
+            }
+        }
+    }
+
+    fn load_palette(&self, palette: VramPalette) -> [u8; 4] {
+        let Some(offset) = palette.offset() else {
+            return utils::GENERIC_PALETTE;
+        };
+        let palette = self.palettes.borrow().read(offset);
+        let brightnesses = self.brightness.borrow();
+        let brts = brightnesses.range(0, 8);
+        utils::parse_palette(palette, brts)
+    }
+}
+
+/*
+struct CharDataLoader {
+    chardata: MemoryView,
+    brightness: MemoryView,
+    palettes: MemoryView,
+}
+
+impl CharDataLoader {
+    pub fn new(sim_id: SimId, memory: &mut MemoryMonitor) -> Self {
+        Self {
+            chardata: memory.view(sim_id, 0x00078000, 0x8000),
+            brightness: memory.view(sim_id, 0x0005f824, 8),
+            palettes: memory.view(sim_id, 0x0005f860, 16),
+        }
+    }
+
+    fn update_character(&self, image: &mut VramImage, palette: VramPalette, index: usize) {
+        if index >= 2048 {
+            return;
+        }
+        let palette = self.load_palette(palette);
+        let chardata = self.chardata.borrow();
+        let character = chardata.range::<u16>(index * 8, 8);
+        for (row, pixels) in character.iter().enumerate() {
+            for col in 0..8 {
+                let char = (pixels >> (col * 2)) & 0x03;
+                image.write((col, row), palette[char as usize]);
+            }
+        }
+    }
+
+    fn update_character_data(&self, image: &mut VramImage, palette: VramPalette) {
+        let palette = self.load_palette(palette);
+        let chardata = self.chardata.borrow();
+        for (row, pixels) in chardata.range::<u16>(0, 8 * 2048).iter().enumerate() {
+            let char_index = row / 8;
+            let row_index = row % 8;
+            let x = (char_index % 16) * 8;
+            let y = (char_index / 16) * 8 + row_index;
+            for col in 0..8 {
+                let char = (pixels >> (col * 2)) & 0x03;
+                image.write((x + col, y), palette[char as usize]);
+            }
+        }
+    }
+
+    fn load_palette(&self, palette: VramPalette) -> [u8; 4] {
+        let Some(offset) = palette.offset() else {
+            return utils::GENERIC_PALETTE;
+        };
+        let palette = self.palettes.borrow().read(offset);
+        let brightnesses = self.brightness.borrow();
+        let brts = brightnesses.range(0, 8);
+        utils::parse_palette(palette, brts)
+    }
+}
+
+impl VramImageLoader for CharDataLoader {
+    type Resource = CharDataResource;
+
+    fn id(&self) -> &str {
+        concat!(module_path!(), "::CharDataLoader")
+    }
+
+    fn add(&self, resource: &Self::Resource) -> Option<VramImage> {
+        match resource {
+            CharDataResource::Character { palette, index } => {
+                let mut image = VramImage::new(8, 8);
+                self.update_character(&mut image, *palette, *index);
+                Some(image)
+            }
+            CharDataResource::CharacterData { palette } => {
+                let mut image = VramImage::new(8 * 16, 8 * 128);
+                self.update_character_data(&mut image, *palette);
+                Some(image)
+            }
+        }
+    }
+
+    fn update<'a>(
+        &'a self,
+        resources: impl Iterator<Item = (&'a Self::Resource, &'a mut VramImage)>,
+    ) {
+        for (resource, image) in resources {
+            match resource {
+                CharDataResource::Character { palette, index } => {
+                    self.update_character(image, *palette, *index)
+                }
+                CharDataResource::CharacterData { palette } => {
+                    self.update_character_data(image, *palette)
+                }
+            }
+        }
+    }
+}
+ */

src/window/vram/utils.rs

@@ -0,0 +1,115 @@
+use egui::{Color32, Image, ImageSource, Response, Sense, TextureOptions, Ui, Widget};
+
+pub const GENERIC_PALETTE: [u8; 4] = [0, 64, 128, 255];
+
+pub fn parse_palette(palette: u8, brts: &[u8]) -> [u8; 4] {
+    let shades = [
+        0,
+        brts[0],
+        brts[2],
+        brts[0].saturating_add(brts[2]).saturating_add(brts[4]),
+    ];
+    [
+        0,
+        shades[(palette >> 2) as usize & 0x03],
+        shades[(palette >> 4) as usize & 0x03],
+        shades[(palette >> 6) as usize & 0x03],
+    ]
+}
+
+pub struct CharacterGrid<'a> {
+    source: ImageSource<'a>,
+    scale: f32,
+    show_grid: bool,
+    selected: Option<usize>,
+}
+
+impl<'a> CharacterGrid<'a> {
+    pub fn new(source: impl Into<ImageSource<'a>>) -> Self {
+        Self {
+            source: source.into(),
+            scale: 1.0,
+            show_grid: false,
+            selected: None,
+        }
+    }
+
+    pub fn with_scale(self, scale: f32) -> Self {
+        Self { scale, ..self }
+    }
+
+    pub fn with_grid(self, show_grid: bool) -> Self {
+        Self { show_grid, ..self }
+    }
+
+    pub fn with_selected(self, selected: usize) -> Self {
+        Self {
+            selected: Some(selected),
+            ..self
+        }
+    }
+
+    pub fn show(self, ui: &mut Ui) -> Option<usize> {
+        let start_pos = ui.cursor().min;
+        let cell_size = 8.0 * self.scale;
+
+        let res = self.ui(ui);
+
+        let grid_width_cells = ((res.rect.max.x - res.rect.min.x) / cell_size).round() as usize;
+
+        if res.clicked() {
+            let click_pos = res.interact_pointer_pos()?;
+            let grid_pos = (click_pos - start_pos) / cell_size;
+            Some((grid_pos.y as usize * grid_width_cells) + grid_pos.x as usize)
+        } else {
+            None
+        }
+    }
+}
+
+impl Widget for CharacterGrid<'_> {
+    fn ui(self, ui: &mut Ui) -> Response {
+        let image = Image::new(self.source)
+            .fit_to_original_size(self.scale)
+            .tint(Color32::RED)
+            .texture_options(TextureOptions::NEAREST)
+            .sense(Sense::click());
+        let res = ui.add(image);
+
+        let cell_size = 8.0 * self.scale;
+        let grid_width_cells = ((res.rect.max.x - res.rect.min.x) / cell_size).round() as usize;
+        let grid_height_cells = ((res.rect.max.y - res.rect.min.y) / cell_size).round() as usize;
+
+        let painter = ui.painter_at(res.rect);
+        if self.show_grid {
+            let stroke = ui.style().visuals.widgets.noninteractive.fg_stroke;
+            for x in (1..grid_width_cells).map(|i| (i as f32) * cell_size) {
+                let p1 = (res.rect.min.x + x, res.rect.min.y).into();
+                let p2 = (res.rect.min.x + x, res.rect.max.y).into();
+                painter.line(vec![p1, p2], stroke);
+            }
+            for y in (1..grid_height_cells).map(|i| (i as f32) * cell_size) {
+                let p1 = (res.rect.min.x, res.rect.min.y + y).into();
+                let p2 = (res.rect.max.x, res.rect.min.y + y).into();
+                painter.line(vec![p1, p2], stroke);
+            }
+        }
+        if let Some(selected) = self.selected {
+            let x1 = (selected % grid_width_cells) as f32 * cell_size;
+            let x2 = x1 + cell_size;
+            let y1 = (selected / grid_width_cells) as f32 * cell_size;
+            let y2 = y1 + cell_size;
+            painter.line(
+                vec![
+                    (res.rect.min + (x1, y1).into()),
+                    (res.rect.min + (x2, y1).into()),
+                    (res.rect.min + (x2, y2).into()),
+                    (res.rect.min + (x1, y2).into()),
+                    (res.rect.min + (x1, y1).into()),
+                ],
+                ui.style().visuals.widgets.active.fg_stroke,
+            );
+        }
+        res
+    }
+}