# Dungeon Canvas Blank Screen - Fix Summary

## Issue
The dungeon editor canvas was displaying only UI elements but the room graphics were blank, despite the rendering pipeline appearing to be set up correctly.

## Root Cause
The background buffers (`bg1` and `bg2`) were never being populated with tile indices from room objects before calling `DrawBackground()`. 

### The Missing Step
1. `Room::RenderRoomGraphics()` would:
   - Copy graphics data to `current_gfx16_`
   - Draw floor pattern via `DrawFloor()`
   - Call `DrawBackground()` to render tiles to pixels

2. **Problem**: `DrawBackground()` expects the buffer to contain tile indices, but only the floor pattern was in the buffer. Room objects were loaded but never converted to tile indices in the buffer!

### How ZScream Does It
- ZScream's `Room.loadLayoutObjects()` and object drawing methods populate `tilesBg1Buffer`/`tilesBg2Buffer` with tile indices
- `GraphicsManager.DrawBackground()` then converts those buffer indices to pixels
- Result: Complete room with floors, walls, and objects

## Solution Implemented

### Changes Made

**File**: `src/app/zelda3/dungeon/room.cc`

1. **Enhanced `RenderRoomGraphics()`** (line 286-315)
   - Added call to `RenderObjectsToBackground()` after `DrawFloor()` but before `DrawBackground()`

2. **Implemented `RenderObjectsToBackground()`** (line 317-383)
   - Iterates through all `tile_objects_`
   - Ensures each object has tiles loaded via `EnsureTilesLoaded()`
   - For each object:
     - Determines correct layer (BG1 vs BG2)
     - Converts each `Tile16` to 4 `TileInfo` sub-tiles
     - Converts each `TileInfo` to word format using `TileInfoToWord()`
     - Places tiles in background buffer using `SetTileAt()`

### Technical Details

**Tile Structure**:
- `Tile16` = 16x16 pixel tile made of 4 `TileInfo` (8x8) tiles
- Arranged as: `[tile0_][tile1_]` (top row), `[tile2_][tile3_]` (bottom row)

**Word Format** (per SNES specs):
```
Bit 15: Vertical flip
Bit 14: Horizontal flip  
Bit 13: Priority/over
Bits 10-12: Palette (3 bits)
Bits 0-9: Tile ID (10 bits)
```

**Buffer Layout**:
- 64x64 tiles (512x512 pixels)
- Buffer index = `y * 64 + x`
- Each entry is a uint16_t word

## Testing

To verify the fix:
1. Build yaze with: `cmake --build build --target yaze`
2. Run yaze and open the dungeon editor
3. Select any room
4. Canvas should now display:
   - ✅ Floor pattern
   - ✅ Wall structures
   - ✅ Room objects
   - ✅ Correct layer separation

## Future Enhancements

- Add layout object rendering (walls from room layout data)
- Optimize tile placement algorithm for different object types
- Add support for animated tiles
- Implement object-specific draw routines (similar to ZScream's `DungeonObjectDraw.cs`)

## Related Files

- **Implementation**: `src/app/zelda3/dungeon/room.cc`
- **Header**: `src/app/zelda3/dungeon/room.h`
- **Buffer**: `src/app/gfx/background_buffer.cc`
- **Tiles**: `src/app/gfx/snes_tile.h`
- **Reference**: `ZeldaFullEditor/GraphicsManager.cs` (ZScream)
- **Reference**: `ZeldaFullEditor/Data/Types/DungeonObjectDraw.cs` (ZScream)

## Build Status

✅ **Compilation**: Success (0 errors)
⚠️ **Warnings**: 21 warnings (pre-existing, unrelated to this fix)