✏️ R-CHR

This is a CHR tile editor for the NES (Famicom) created using Rust and egui.

In addition to the basic features of YY-CHR, it includes 10 types of drawing tools, PNG import, and continuous scrolling display, all designed to enhance usability.

Build and Launch

cargo run --release

Requires Rust 1.80 or later.

Cargo will automatically fetch the required libraries.

Basic Usage

Open File

You can open a file in Bank View by selecting it from File → Open… or by dragging and dropping it into the window.

Supported Formats:

• .nes — iNES format. Supports ROMs that include CHR-ROM
• .bin — Headerless raw CHR binary
• .zip — Automatically extract and load the first .nes file in the ZIP

New File

File → New File creates an empty 16KB CHR data file (newfile).

Save

Action	Shortcut
Save	⌘S / Ctrl+S
Save As	⌘⇧S / Ctrl+Shift+S

When there are unsaved changes, an asterisk (*) is shown in the title bar. A confirmation dialog appears when you try to close the window.

Layout

• Bank View (left): Minimum width 410px. Integer-scale zoom to fit window width
• Dot Editor (center): Resizable. Minimum 180px
• Info Panel (right): Fixed width 245px

Bank View

Scrolling

Displays all CHR data as a vertical texture with 16 tiles per row (128px). 1 row = 16 tiles × 16 bytes = 0x100 bytes. Use the scrollbar to navigate up and down.

Address Jump

Enter a hex address in the "Address:" field in the toolbar and press the Go button or Enter to jump to that position.

Focus Size

The selection block (= editing unit in the Dot Editor) can be switched between 5 sizes.

Button	Size	Tiles
8	8×8 px	1×1 tiles
16	16×16 px	2×2 tiles
32	32×32 px	4×4 tiles
64	64×64 px	8×8 tiles
128	128×128 px	16×16 tiles

Tile Selection

Clicking a tile sets it as the selection origin, and the Dot Editor displays the tile block for the current focus size.

Dot Editor

The selected tile block (based on focus size) is displayed enlarged for editing. Click the toolbar icons or use keyboard shortcuts to select tools.

Common Operations

Action	Description
Right-click	Eyedropper — sets the clicked pixel's color as the drawing color

Drawing Tools

🖊 Pencil

Click and drag to draw one pixel at a time. Even when dragging across multiple tiles, all changes can be undone in a single Undo step.

⬡ Pencil (Pattern)

Draws in a checkerboard pattern using (x+y) % 2 parity from the click origin, skipping every other pixel. The pattern remains seamless even across tile boundaries.

／ Line

Click to set a start point and drag to draw a straight line. Uses Bresenham's algorithm for integer-precise lines. A real-time preview is shown while dragging. Confirmed on button release.

□ Rectangle (Outline)

Drag to specify two corners and draw only the outer border. Confirmed on button release.

■ Rectangle (Fill)

Fills the entire interior of the rectangle. Confirmed on button release.

▨ Rectangle (Pattern)

Fills the rectangle area with a checkerboard pattern based on the origin parity. Confirmed on button release.

○ Ellipse (Outline)

Defines an ellipse by its bounding box (two diagonal corners) and draws the outline only. Combines left/right row endpoints and top/bottom column endpoints for a gap-free outline. Confirmed on button release.

● Ellipse (Fill)

Fills the entire interior of the ellipse using a scanline method. Confirmed on button release.

🪣 Flood Fill

Fills all connected pixels of the same color index at the clicked position using BFS (breadth-first search). 4-directional connectivity. Does nothing if the clicked color matches the drawing color.

🔲 Stamp

A two-phase copy & paste tool.

Phase	Action	Behavior
Select (Phase 1)	Drag	Preview the selection with a dashed border
	Release	Confirm the area and copy it into the buffer
Paste (Phase 2)	Drag	Dashed outline + pixel preview follows the cursor
	Release	Write to CHR (buffer is retained)
	Right-click	Cancel and return to Phase 1

The buffer is retained so you can stamp the same content multiple times.

Copy & Paste

Action	Shortcut
Copy	⌘C / Ctrl+C
Paste	⌘V / Ctrl+V

Copies the current focus-size tile block to the clipboard and pastes it at the selected tile position. Paste can be undone.

Keyboard Shortcuts

Key	Action
↑ ↓ ← →	Move selected tile by 1 tile
Z / X / C / V	Switch palette set 0–3
⌘N / Ctrl+N	New file
⌘Z / Ctrl+Z	Undo
⌘C / Ctrl+C	Copy tiles
⌘V / Ctrl+V	Paste tiles
⌘S / Ctrl+S	Save
⌘⇧S / Ctrl+Shift+S	Save As

When the selected tile moves off-screen with the arrow keys, the view auto-scrolls.

Palette

Palette Panel

Displays the NES palette (DAT palette) as 4 sets × 4 colors. Select a cell and choose a color from the NES 64-color picker to change it.

Palette Set Switching

Switch the set used for Bank View rendering with the Z / X / C / V keys.

Palette Menu

The following operations are available from the Palette menu.

Menu Item	Description
Open PAL file…	Load a .pal file (192 bytes = 64 colors × 3 RGB bytes) and overwrite the master palette
Open DAT file…	Load a .dat file (16+ bytes) and update the palette sets
Save DAT file…	Export the current palette sets as a .dat file
Reset Master Palette (NES Standard)	Restore the built-in NES standard 64-color palette

Default Palette

On startup, assets/rchr.pal (master palette) and assets/rchr.dat (palette sets) are loaded automatically. Compatible with YY-CHR format.

PNG Import

While YY-CHR's "Paste Image" only supports 8bpp indexed BMP / 8-bit indexed PNG, r-chr accepts all of the following:

• Indexed color PNG (1-bit / 2-bit / 4-bit / 8-bit)
• Full color PNG (RGB / RGBA)
• PNG with transparency (tRNS chunk / alpha channel)

How to Open

• File → Import PNG… to open a file selection dialog
• Drag and drop a PNG file onto the window

A NES / BIN file must be opened first.

Import Dialog

After selecting a PNG, a confirmation dialog appears.

┌────────────────────────────────────────────────────────┐
│  PNG Import                                            │
│                                                        │
│  File: sprite.png  (32×32 px = 4×4 tiles)             │
│                                                        │
│  Mapping Strategy:                                     │
│  ● Palette Match (recommended)  ○ Index Direct  ○ RGB Approx │
│                                                        │
│  ⚠ 3 colors could not be exactly matched and were approximated │
│  ⚠ 1 transparent palette entry → mapped to index 0    │
│                                                        │
│  Preview (after conversion):                           │
│  [Preview rendered in converted CHR colors]            │
│                                                        │
│  Paste at: Tile 0 (0x000000)                          │
│                                                        │
│         [Cancel]      [Paste]                          │
└────────────────────────────────────────────────────────┘

• Paste at: The currently selected tile in Bank View is used as the origin
• After pasting: Can be undone with Undo (⌘Z / Ctrl+Z)
• Mapping Strategy: Switching via radio button updates the preview in real time

Mapping Strategies

3 methods are available for converting PNG pixels to CHR color indices (0–3). The strategy is auto-selected based on the file type, but can be changed manually in the dialog.

Palette Match (recommended for Aseprite)

Auto-selected when: Indexed color PNG with a PLTE chunk

Ideal when working in Aseprite with the NES master palette.

Conversion flow:

PLTE[i] RGB
  → Nearest-neighbor match among NES master palette 64 colors
  → Select the closest of the 4 colors in the current DAT palette set
  → Convert to CHR index 0–3

Aseprite workflow:

1. Create a sprite in Indexed Color mode in Aseprite
2. Set the palette from rchr.pal or the game's actual NES palette
3. File → Export as PNG (keeping indexed color mode)
4. Open the file in r-chr and select the target tile
5. File → Import PNG… or D&D to import → "Palette Match" is auto-selected
6. Check the preview and press Paste

Index Direct

Auto-selected when: Indexed color PNG without a PLTE chunk

Pixel index value mod 4 → CHR index 0–3

Use case: When the first 4 palette entries (indices 0–3) are intentionally mapped to CHR 0–3.

RGB Approximate

Auto-selected when: Full color PNG (RGB / RGBA)

Each pixel's RGB
  → Calculate RGB distance to the 4 colors in the current DAT palette set
  → Map to the closest color index 0–3 → write to CHR

Use case: Full color PNGs, screenshots, images converted from BMP, or any arbitrary PNG. Color reproduction is approximate only. Accuracy improves when the DAT palette matches the game's actual palette.

Handling Transparency

When a PNG contains transparent pixels (tRNS chunk / alpha channel), they are automatically mapped to CHR index 0.

Format	Transparency Condition
Indexed PNG (with tRNS)	Palette entries with alpha = 0 in tRNS
RGBA PNG	Pixels with alpha value < 128

In NES CHR, index 0 corresponds to the background color (transparent color for sprites), so mapping transparent pixels to 0 ensures the sprite appearance is set correctly. The count of transparent pixels is shown in the dialog's warning area.

Undo

All drawing operations and PNG imports support Undo.

Operation	Undo Unit	Max Steps
Dot Editor editing (pencil, drag)	All tile changes in one drag stroke	100
Line / Rectangle / Ellipse / Flood Fill	All tile changes for one shape	100
Stamp	All tile changes in one stamp	100
Tile Paste	All tile changes in one paste	100
PNG Import	All affected tiles in one batch	100

File Structure

src/
  main.rs              — Entry point & window setup
  native_menu.rs       — macOS native menu (muda crate)
  editor/
    mod.rs
    app.rs             — App state & main loop (eframe::App)
    bank_view.rs       — Bank View (full CHR display & tile selection)
    clipboard.rs       — Tile copy & paste
    dot_editor.rs      — Dot Editor & 10 drawing tools
    file_ops.rs        — Open / Save / New file operations
    info_panel.rs      — Right panel (palette, draw color, info display)
    keyboard.rs        — Keyboard shortcut handling
    png_import.rs      — PNG import dialog
    setup.rs           — Font setup
    theme.rs           — Color, font & size constants
    mac/
      mod.rs
      menu_bar.rs      — egui menu bar (non-macOS)
      menu_events.rs   — macOS native menu event handling
  io/
    mod.rs
    chr.rs             — CHR decode / encode / rendering
    nes.rs             — iNES format parser / RomData type
    png.rs             — PNG / BMP import (mapping & CHR write)
  model/
    mod.rs
    palette.rs         — NES palette (MasterPalette / DatPalette)

assets/
  rchr.pal             — Default master palette (YY-CHR compatible .pal)
  rchr.dat             — Default palette sets (YY-CHR compatible .dat)
  rchr.bin             — Default CHR data displayed on startup (R-CHR logo)
  nes.pal              — NES standard 64-color palette (for reset)
  icons/               — SVG icons for toolbar & drawing tools

References & Credits

This tool was developed with reference to YY-CHR. YY-CHR is a well-established NES / SNES CHR editor, and served as a major reference for the basic interface design and CHR format handling.

License

This project is licensed under the MIT License. See the LICENSE file for details.

Author

Daisuke Takayama

• @webcyou
• @panicdragon
• https://github.com/webcyou
• https://github.com/webcyou-org
• https://github.com/panicdragon
• https://www.webcyou.com/