Map Support - Chimera

Chimera provides extensive map support features, including running Custom Edition maps on retail Halo PC, compressed map support, and automatic map downloading.

Custom Edition Maps on Retail

Chimera enables Custom Edition map support on the base Halo PC (retail) installation.

Why This Matters

Problem: Halo PC (retail) and Halo Custom Edition use different resource maps, making them incompatible.Solution: Chimera allows retail to load Custom Edition maps by using CE’s resource maps.

Setup Instructions

Obtain Custom Edition Resource Maps

Get these files from the Halo Custom Edition installation:

bitmaps.map
loc.map
sounds.map

Rename the Files

Add custom_ prefix to each file:

bitmaps.map → custom_bitmaps.map
loc.map → custom_loc.map
sounds.map → custom_sounds.map

Copy to Maps Folder

Place the renamed files in your Halo PC maps folder.

Verify

Chimera will automatically detect all three files and enable Custom Edition map support.

DO NOT overwrite your original bitmaps.map or sounds.map files. You need these to load Halo PC maps.Chimera will not enable this feature if any of the three files are missing.

Extracting Without Installing

You can extract resource maps without installing Custom Edition:

Windows
Linux

Use 7-Zip to extract files from the Custom Edition installer:

Right-click the installer
Select “7-Zip” → “Open archive”
Extract the three resource map files
Rename them with custom_ prefix

Use p7zip:

7z x HaloCESetup.exe
mv bitmaps.map custom_bitmaps.map
mv loc.map custom_loc.map
mv sounds.map custom_sounds.map

Compressed Maps

Chimera supports maps compressed with the zstd compression algorithm.

Benefits

Smaller File Sizes

Drastically reduce map file sizes with blazingly fast zstd compression

Fast Decompression

zstd is extremely fast - decompression happens nearly instantly

RAM or Disk

Decompress directly to RAM or use temp files

Transparent

Works automatically - no user intervention needed

How It Works

// Chimera detects compressed maps automatically
// Decompression happens transparently on load

Decompression behavior:

Maps in RAM Enabled
Maps in RAM Disabled

If the enable_map_memory_buffer setting is enabled:

[memory]
enable_map_memory_buffer=1
map_size=1024  ; Buffer size in MiB

Compressed maps decompress directly into RAM - no temp files.

Location: src/chimera/map_loading/compression.cpp

Compression Tool

Use the chimera-compress tool to compress maps:

chimera-compress input.map output.map

The compression tool is a separate utility available in the Chimera repository.

Technical Details

// Supported compressed engine types
CACHE_FILE_CUSTOM_EDITION_COMPRESSED
CACHE_FILE_RETAIL_COMPRESSED  
CACHE_FILE_DEMO_COMPRESSED

Chimera:

Detects compressed map header
Validates compression format
Decompresses using zstd
Converts header to uncompressed format
Loads map normally

Map Downloading

Chimera automatically downloads missing maps when joining servers.

How It Works

Join Server

You join a server hosting a map you don’t have.

Automatic Detection

Chimera detects the missing map.

Download

Map is downloaded from the configured repository (default: HAC2 Map repo).

Storage

Map is saved to the download directory and you join the game.

Configuration

[memory]

; Download directory (default: <profiles>/chimera/maps)
download_map_path=C:\Users\YourName\Documents\My Games\Halo\chimera\maps

; Font for download progress
download_font=small

; URL template for downloading
download_template=http://maps.halonet.net/halonet/locator.php?format=inv&map={map}&type={game}

; Allow downloading retail maps (UNSAFE - see warning below)
download_retail_maps=0

URL Template Variables

The download_template supports these replacements:

Variable	Replaced With
`{map}`	Map name
`{game}`	Game type (“halor” = PC, “halom” = CE, “halod” = trial)
`{server}`	Current server IP
`{password}`	Server password
`{mirror<x,y,...>}`	Try each mirror until one works

Example with mirrors:

download_template=http://{mirror=mirror1.com,mirror2.com,mirror3.com}/maps/{map}.map

Retail Map Downloads

Downloading retail maps is OFF by default due to compatibility risks.Enable only if you have:

English copy of retail Halo PC
Matching bitmaps.map and sounds.map files

Incompatible maps will result in corrupt assets and extremely loud sounds (“earrape”).

; Only enable if you know what you're doing
download_retail_maps=1

Default Repository

By default, Chimera uses the HAC2 Map Repository:

http://maps.halonet.net/halonet/locator.php?format=inv&map={map}&type={game}

Maps in RAM

Load maps directly into RAM for better performance.

Benefits

Faster Loading

Eliminate disk I/O bottlenecks

Reduced Stuttering

No disk access during gameplay

Better for SSDs

Reduce SSD wear from repeated map loads

Compressed Maps

Decompress directly to RAM

Requirements

You need an LAA-patched executable to use maps in RAM.LAA (Large Address Aware) allows 32-bit applications to use more than 2 GB of RAM.

Configuration

[memory]

; Enable loading maps into RAM
enable_map_memory_buffer=1

; Buffer size in MiB (for UI map + one non-UI map)
map_size=1024

; Show decompression benchmark
benchmark=1

Recommended size: 1024 MiB (1 GB) is sufficient for most maps.

Benchmark Display

Enable benchmark=1 to see load times:

Map loaded in 123.45 ms
Decompressed 45.2 MB in 67.89 ms

Map Loading Optimizations

Fast Loading

Chimera drastically improves map loading times.

The Problem

Halo Custom Edition CRC32s every map on startup:

Small maps folder: Minor delay
Large maps folder: Minutes of startup time

Some mods cache CRC32s, but this defeats the purpose (can join with mismatched maps).

The Solution

Chimera CRC32s maps when you load them, not at startup:

Zero startup delay regardless of maps folder size
Maintains server validation (proper CRC32 checking)
True fix, not a workaround

Location: src/chimera/map_loading/fast_load.cpp

128 MiB Map Leak Fix

Fixes file descriptor leaks with large maps. The Bug:

if (map_size > 128 MiB) {
    // Opens file multiple times
    // Only closes once
    // File descriptors leak
    // Eventually: out of file handles
}

The Fix: Removes the problematic file size check. Location: src/chimera/fix/leak_descriptors.cpp

Campaign in Custom Edition

Chimera re-enables the campaign menu in Custom Edition.

Feature: If all campaign maps are available in the maps folder, Chimera will enable the “Campaign” menu option.Just like retail: This restores functionality removed in Custom Edition.

Required maps:

a10.map
a30.map
a50.map
b30.map
b40.map
c10.map
c20.map
c40.map
d20.map
d40.map

Map Hacks and Compatibility

Chimera includes a map compatibility system for legacy maps.

Compatibility List

Enable/disable the compatibility list:

[maps]
map_compatibility_list=1  ; Default: enabled

Purpose: Support legacy maps that depend on:

Gearbox renderer regressions
Legacy Chimera hacks
Specific rendering quirks

Location: src/chimera/fix/map_hacks/map_hacks.cpp

Most modern maps don’t need compatibility hacks. This is mainly for very old Custom Edition maps.

CRC32 Handling

Chimera properly validates map CRC32 checksums.

Why CRC32 Matters

Server Validation

Servers check CRC32 to ensure all players have the same map:

~99.999999976% certainty of identical maps
Prevents crashes from mismatched content
Ensures fair gameplay

Modified Maps

Using a modified map will cause CRC32 mismatch:

Error: CRC32 does not match server

This is intentional - prevents crashes.

Forging CRC32

If you want to use a modified Custom Edition map on a Custom Edition server:

Modify your map
Use a tool to forge the CRC32 to match the original
Join server

Only do this if your modifications won’t cause crashes. You’ve been warned.

chimera.ini

Main configuration file

Memory Settings

Maps in RAM configuration

Map Path

Custom map directories

Commands

Map-related commands

Technical Implementation

Key map loading code locations:

src/chimera/map_loading/
├── compression.cpp       # Compressed map support
├── fast_load.cpp        # Fast CRC32 loading
├── leak_descriptors.cpp # 128 MiB leak fix
├── laa.cpp              # Large address aware
└── map_loading.cpp      # Core loading system

Get Started

Features

Configuration

Advanced

​Custom Edition Maps on Retail

​Why This Matters

​Setup Instructions

​Extracting Without Installing

​Compressed Maps

​Benefits

Smaller File Sizes

Fast Decompression

RAM or Disk

Transparent

​How It Works

​Compression Tool

​Technical Details

​Map Downloading

​How It Works

​Configuration

​URL Template Variables

​Retail Map Downloads

​Default Repository

​Maps in RAM

​Benefits

Faster Loading

Reduced Stuttering

Better for SSDs

Compressed Maps

​Requirements

​Configuration

​Benchmark Display

​Map Loading Optimizations

​Fast Loading

​128 MiB Map Leak Fix

​Campaign in Custom Edition

​Map Hacks and Compatibility

​Compatibility List

​CRC32 Handling

​Why CRC32 Matters

​Related Configuration

chimera.ini

Memory Settings

Map Path

Commands

​Technical Implementation

Build docs developers (and LLMs) love

Custom Edition Maps on Retail

Why This Matters

Setup Instructions

Extracting Without Installing

Compressed Maps

Benefits

How It Works

Compression Tool

Technical Details

Map Downloading

How It Works

Configuration

URL Template Variables

Retail Map Downloads

Default Repository

Maps in RAM

Benefits

Requirements

Configuration

Benchmark Display

Map Loading Optimizations

Fast Loading

128 MiB Map Leak Fix

Campaign in Custom Edition

Map Hacks and Compatibility

Compatibility List

CRC32 Handling

Why CRC32 Matters

Related Configuration

Technical Implementation