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Godot 4.2 Lightmap Baker Freezes at 80% - How to Fix

Encountering a lightmap baking process in Godot 4.2 that freezes or hangs at 80% completion can be frustrating, especially when you're trying to create beautiful baked lighting for your game. This issue often indicates problems with memory allocation, complex geometry processing, or lightmap resolution settings. This guide provides comprehensive solutions to diagnose and fix lightmap baking freezes in Godot 4.2.

The Problem: Lightmap Baker Hangs at 80%

Common Symptoms:

  • Lightmap baking progress bar stops at approximately 80%
  • Godot Editor becomes unresponsive during baking
  • High CPU/memory usage by Godot process
  • No error messages appear in the Output panel
  • Baking process never completes, even after extended wait times
  • Editor must be force-closed to recover

Why This Happens: The 80% mark in lightmap baking typically corresponds to the final lightmap generation and compression stage. Common causes include:

  • Insufficient System Memory: Large lightmaps or complex scenes require significant RAM
  • Excessive Lightmap Resolution: Very high resolution settings can overwhelm the system
  • Complex Geometry: Dense meshes with many polygons slow down processing
  • Too Many Light Sources: Multiple lights increase computation complexity
  • Disk Space Issues: Temporary files during baking may fill available disk space
  • Godot 4.2 Bugs: Specific version issues with lightmap baking pipeline

Solution 1: Reduce Lightmap Resolution (Most Common Fix)

High lightmap resolution is the most frequent cause of baking freezes. Reducing resolution often resolves the issue immediately.

Step-by-Step Fix:

  1. Open Your Scene: Load the scene that's experiencing the baking freeze.

  2. Select Geometry Nodes: Select all MeshInstance3D nodes that use lightmaps in your scene.

  3. Adjust Lightmap Scale:

    • In the Inspector, find the Lightmap Scale property
    • Change from 1.0 (default) to 2.0, 4.0, or 8.0
    • Higher values = lower resolution = faster baking
    • Recommended: Start with 4.0 for testing

  4. Check Lightmap UV2:

    • Ensure all meshes have proper UV2 (lightmap UV) coordinates
    • If missing, select mesh and go to Mesh > Generate Lightmap UV2
    • This ensures efficient lightmap packing

  5. Rebake Lightmaps:

    • Go to Project > Project Settings > Rendering > Lightmapping
    • Click Bake Lightmaps or use Bake Lightmaps from the menu
    • Monitor progress; it should complete without freezing

Verification: The baking process should complete successfully. If it still freezes, try even lower resolution (scale 8.0 or 16.0).

Solution 2: Increase Available Memory

Lightmap baking is memory-intensive. Ensuring adequate RAM can prevent freezes.

Step-by-Step Fix:

  1. Close Unnecessary Applications:

    • Close browsers, video editors, and other memory-intensive programs
    • Free up as much RAM as possible before baking

  2. Check System Memory:

    • Windows: Open Task Manager (Ctrl+Shift+Esc) and check available RAM
    • macOS: Open Activity Monitor and check Memory Pressure
    • Linux: Use free -h command to check available memory
    • Minimum Recommended: 8GB free RAM for lightmap baking

  3. Increase Virtual Memory (Windows):

    • Go to Control Panel > System > Advanced system settings
    • Click Settings under Performance
    • Go to Advanced tab > Change under Virtual memory
    • Uncheck "Automatically manage paging file size"
    • Set custom size: Initial 8192 MB, Maximum 16384 MB
    • Click Set and restart computer

  4. Restart Godot Editor:

    • Close Godot completely
    • Reopen your project
    • Attempt lightmap baking again

Verification: Monitor memory usage during baking. If memory usage stays below 90%, baking should proceed without freezing.

Solution 3: Optimize Scene Geometry

Complex geometry with excessive polygons can cause the lightmap baker to hang during processing.

Step-by-Step Fix:

  1. Reduce Polygon Count:

    • Select high-poly meshes in your scene
    • Use mesh decimation tools (Blender, external tools) to reduce complexity
    • Target: Keep meshes under 10,000-20,000 triangles per object

  2. Simplify Lightmap Geometry:

    • Only bake lightmaps on important, visible geometry
    • Disable lightmap baking on small, distant, or non-critical objects
    • Set Lightmap Scale to 0 (disabled) for objects that don't need baked lighting

  3. Check for Overlapping Geometry:

    • Overlapping meshes can cause baking issues
    • Ensure no duplicate or intersecting geometry
    • Use Godot's MeshInstance3D > Geometry > Generate Lightmap UV2 to fix UV issues

  4. Reduce Scene Complexity:

    • Temporarily hide or remove non-essential objects
    • Bake lightmaps in smaller sections
    • Combine multiple small objects into single meshes where possible

Verification: Baking should complete faster and without freezing. Monitor the progress bar; it should advance smoothly past 80%.

Solution 4: Adjust Lightmap Baking Settings

Godot 4.2's lightmap baking settings can be optimized to prevent freezes.

Step-by-Step Fix:

  1. Open Project Settings:

    • Go to Project > Project Settings
    • Navigate to Rendering > Lightmapping

  2. Adjust Lightmap Settings:

    • Bake Quality: Set to Low or Medium instead of High (for testing)
    • Bake Subdiv: Reduce subdivision level (lower = faster, less detailed)
    • Bake Bias: Keep default (0.00001) unless experiencing light bleeding

  3. Limit Light Sources:

    • Reduce the number of lights in your scene
    • Use fewer DirectionalLight3D and OmniLight3D nodes
    • Consider combining multiple lights into fewer, more efficient ones

  4. Optimize Lightmap Atlas Size:

    • In Project Settings, set Lightmap Atlas Max Size to 2048 or 1024 (from default 4096)
    • Smaller atlas = less memory usage = faster baking

  5. Enable Progressive Baking (if available):

    • Some Godot versions support progressive baking
    • This allows you to see results incrementally and cancel if needed

Verification: Baking should complete without freezing. If successful, gradually increase quality settings to find the optimal balance.

Solution 5: Clear Godot Cache and Temporary Files

Corrupted cache or temporary files can cause lightmap baking to hang.

Step-by-Step Fix:

  1. Close Godot Editor: Ensure Godot is completely closed.

  2. Locate Godot Cache:

    • Windows: %APPDATA%\Godot\
    • macOS: ~/Library/Application Support/Godot/
    • Linux: ~/.local/share/godot/

  3. Clear Project-Specific Cache:

    • Navigate to your project folder
    • Delete .godot/ folder (hidden folder)
    • Warning: This will reset some project settings; you may need to reconfigure

  4. Clear Lightmap Data:

    • In your project folder, delete any .lightmap files or folders
    • Delete res://.godot/imported/ folder contents related to lightmaps

  5. Reopen Project:

    • Open Godot and load your project
    • Godot will regenerate cache files
    • Attempt lightmap baking again

Verification: Fresh cache should eliminate any corruption issues. Baking should proceed normally.

Solution 6: Update or Downgrade Godot Version

Godot 4.2 may have specific bugs affecting lightmap baking. Updating or using a stable version can resolve issues.

Step-by-Step Fix:

  1. Check Current Version:

    • In Godot, go to Help > About
    • Note your current Godot version (e.g., 4.2.0, 4.2.1)

  2. Update to Latest 4.2 Version:

    • Download latest Godot 4.2.x from godotengine.org
    • Install new version
    • Open your project with updated version
    • Test lightmap baking

  3. Or Downgrade to Stable 4.1:

    • If 4.2 continues to have issues, try Godot 4.1 LTS
    • Note: May require minor project adjustments
    • Test if lightmap baking works in 4.1

  4. Check Release Notes:

    • Review Godot release notes for lightmap baking fixes
    • Look for known issues in your specific version

Verification: Updated or stable version should have fewer bugs. Test lightmap baking to confirm fix.

Solution 7: Bake Lightmaps in Smaller Batches

If your entire scene is too complex, bake lightmaps in smaller sections.

Step-by-Step Fix:

  1. Divide Scene into Sections:

    • Create separate scenes for different areas (e.g., room1.tscn, room2.tscn)
    • Or use Godot's scene instancing to separate complex areas

  2. Bake Each Section Separately:

    • Open one section/scene at a time
    • Bake lightmaps for that section only
    • Save the baked lightmap data

  3. Combine Results:

    • Load all sections into main scene
    • Lightmaps should work together if UV coordinates are correct
    • Test final combined scene

  4. Use Lightmap Probes (Alternative):

    • Instead of full lightmap baking, use LightmapGI with probes
    • Less memory-intensive than full scene baking
    • Good for dynamic or large scenes

Verification: Smaller batches should bake successfully. Combine results for final scene.

Solution 8: Check Disk Space and Permissions

Insufficient disk space or write permissions can cause baking to hang when writing temporary files.

Step-by-Step Fix:

  1. Check Available Disk Space:

    • Ensure at least 5-10GB free space on your project drive
    • Lightmap baking creates temporary files that can be large

  2. Check Write Permissions:

    • Ensure Godot has write permissions to project folder
    • On Linux/macOS, check folder permissions: chmod -R 755 /path/to/project

  3. Move Project to Faster Drive:

    • If using slow HDD, move project to SSD
    • Faster disk I/O can prevent hangs during file operations

  4. Check Antivirus/File Protection:

    • Temporarily disable antivirus real-time scanning on project folder
    • Some antivirus software can interfere with file operations during baking

Verification: Adequate disk space and permissions should allow baking to complete file operations without hanging.

Prevention Tips

  • Start with Low Resolution: Begin with lower lightmap resolution, increase gradually
  • Optimize Geometry Early: Keep polygon counts reasonable from the start
  • Monitor System Resources: Watch memory and CPU usage during baking
  • Bake Incrementally: Test baking on small scenes before full scene
  • Keep Godot Updated: Use latest stable versions with bug fixes
  • Use Lightmap Probes: For dynamic scenes, consider probes instead of full baking

Common Error Messages (Related to Baking Freezes)

While a freeze might not produce explicit errors, these messages often precede or are related to the underlying cause:

  • Out of memory (Indicates insufficient RAM)
  • Lightmap atlas too large (Resolution settings too high)
  • Failed to generate lightmap UV2 (Geometry issues)
  • Disk full (Insufficient disk space for temporary files)

Related Problems

Don't let lightmap baking freezes slow down your development! Apply these fixes to get your baked lighting working smoothly in Godot 4.2.