The .RBGI Format SDK is the open-source part of MozAluz RBGI Tools. It contains the format DLL source files, headers, documentation, and example code for the public file format layer.
The SDK is built around SharedRBGIformat.dll, RbgiFormat.h, and
RbgiFormat.cpp. It is written in C++17 with Qt 6 and is used for loading, saving,
validating, and inspecting .RBGI files.
MozAluz RBGI Viewer and MozAluz RBGI Editor remain official closed-source tools. The SDK exists so other programs can support .RBGI files without needing the Viewer or Editor source code.
Get the public .RBGI Format SDK source code from GitHub, read the SDK README, or download the V1 source package. This SDK repo should only contain the format layer, not the closed-source Viewer or Editor projects.
.RBGI means Render Background Image. It was made so tools like Source BSP Explorer could use a custom render-background / skybox-background file type instead of using normal image extensions directly.
A real RBGI v1 file is not just a renamed PNG. It is a small custom container that stores a binary RBGI header, compact JSON metadata, and embedded PNG image bytes.
REAL RBGI V1: [ RBGI HEADER ][ JSON METADATA ][ PNG IMAGE DATA ]
The file starts with the magic bytes RBGI. After that, the SDK reads a
little-endian header containing the format version, header size, image width, image height,
image mode, reserved flags, metadata size, and embedded PNG size.
Metadata is stored as a compact JSON object. It can describe the asset name, source project, creator tool, description, or other information needed by editors, viewers, or render tools.
The actual picture is stored as embedded PNG data. This keeps the image data simple and reliable, while the RBGI wrapper gives the file a custom identity and room for extra render metadata.
Older .RBGI files may be normal PNG files renamed to .RBGI. The SDK still tries to
load those legacy files so old backgrounds do not become useless.
OFFSET TYPE NAME 0 char[4] magic = "RBGI" 4 quint16 version = 1 6 quint32 headerSize = 38 10 quint32 width 14 quint32 height 18 quint32 image mode 22 quint32 flags 26 quint64 pngSize 34 quint32 metadataSize 38 byte[] compact JSON metadata 38+M byte[] embedded PNG bytes
The SDK has multiple image mode values so .RBGI files can describe how they are meant to be used.
0 = FlatImage 1 = RenderBackground 2 = SkyBoxSingleTexture 3 = SkyBoxCubeTexture
1. Read the file bytes. 2. Check if the file starts with "RBGI". 3. If yes, load it as a real RBGI v1 file. 4. If no, try to load it as PNG image data. 5. If PNG loading works, mark it as a legacy renamed-PNG RBGI. 6. If both paths fail, the file is invalid.
When loading a file, the SDK returns a document-style result with the decoded image, width, height, metadata, image mode, version, flags, embedded PNG bytes, legacy-file status, validity state, and an error message if something failed.
The SDK includes safety checks for invalid files. It rejects empty files, unsupported versions, invalid metadata JSON, invalid PNG data, and files that are neither real RBGI v1 files nor valid legacy PNG data.
MAX METADATA SIZE: 8 MiB MAX PNG SIZE: 512 MiB
New tools should save real RBGI v1 files using the SDK's real save function. Legacy renamed-PNG saving should only be used when older compatibility is needed.