Collaborative editing of 3D world using Castle Game Engine and mORMot2

Introduction

A collaboration of two open-source projects, both using modern Pascal:

1. Castle Game Engine - 3D and 2D game engine, with editor, lots of rendering features and powerful API. This provides local display and editing of the 3D world.

2. mORMot 2 - ORM / SOA / MVC framework. This provides the ORM -- a way to express the resulting world as objects that can be send over the the network and persisted on the server side.

In effect, you have a fun application where multiple people can connect and rearrange a 3D world. Example fun you can do:

• Design city from a buildings.
• Design a room from furniture.
• Arrange chess pieces on a board.

Features

You can:

• Add boxes, spheres, and random glTF assets from the client data.
• Duplicate objects.
• Remove objects.
• Select, move, rotate, scale the 3D objects (using new CastleTransformManipulate unit).
• Navigate in the world (use AWSD to move, hold right mouse button to look around).

The state of the 3D world is persistent. That is, all the operations on 3D objects (add, remove, transforming) are saved automatically. You can close the client application at any time, open it again, and the world will be in the same state as you left it. Technically:

• The client sends all the changes to the server.
• The server in turn persists the state of the 3D world to a database (Sqlite).

Note that the current camera and selection state is not saved, deliberately. Conceptually, they are not part of the "3D world state". Also, we wanted to keep this example code simple :) But saving them could be easily addded, as additional ORM classes.

Screenshots

ORM usage

This uses ORM to synchronize the 3D world between the server and clients.

• It means that we have a class TOrmCastleTransform (defined in SharedData unit) that represents a single 3D object in our world.

• We use mORMot to synchronize the state of this class. Client synchronizes state with server, and server synchronizes state with database (Sqlite) on disk.

• On the client side, this is also synchronized with Castle Game Engine components -- one TOrmCastleTransform corresponds to one TCastleTransform (plus one child, like TCastleScene or TCastleSphere or TCastleBox) in the 3D world.

• ORM is a powerful approach when you want to think "I have a state of my objects, I want to synchronize it over the network". There's no need for much of application-specific server code -- the server stores the state of the objects and out-of-the-box allows the client to modify this state, by adding/updating/removing objects. So you don't need to deal with services, endpoints, JSON parsing, database reading/saving -- this is taken care of by mORMot.

• Note that this isn't the only way to use mORMot. You can also use mORMot to expose specific services (endpoints), and to implement them in any way, e.g. by database access. Just for this case, using ORM for 100% of operations made sense.

The main unit where the ORM state is visualized and manipulated is GameViewEdit.

The mORMot usage in this demo follows a simple example ex/ThirdPartyDemos/martin-doyle/02-HttpClientServerORM/. If you want to explore this approach without Castle Game Engine, you can start with that example.

Building

Get mORMot 2. Follow the quick-start guide there. In short:

git clone https://github.com/synopse/mORMot2/
cd static/
  wget https://synopse.info/files/mormot2static.7z
  7z x mormot2static.7z
cd ../
lazbuild packages/lazarus/mormot2.lpk
lazbuild packages/lazarus/mormot2ui.lpk

If you want to build using CGE editor or CGE command-line build tool, then edit these files:

• castle_mormot_client/CastleEngineManifest.xml
• castle_mormot_server/CastleEngineManifest.xml

to 1. indicate the proper (absolute or relative) directory where mORMot2 is located, 2. indicate the proper path to static files, if you compile for something else than win64.

NOTE: There's no need to edit the CastleEngineManifest.xml files if you build using Lazarus or Delphi IDEs -- in this case, if you followed the mORMot2 quick-start guide, you're all set.

Both client and server can be built just like all Castle Game Engine projects:

Compile by:

• CGE editor. Just use menu items "Compile" or "Compile And Run".

• Or use CGE command-line build tool. Run castle-engine compile in this directory.

• Or use Lazarus. Open in Lazarus castle_mormot_client.lpi (or castle_mormot_server.lpi) file and compile / run from Lazarus. Make sure to first register CGE Lazarus packages.

• Or use Delphi. Open in Delphi castle_mormot_client.dproj (or castle_mormot_server.dproj) file and compile / run from Delphi. See CGE and Delphi documentation for details.

TODO

• For collaborative editing, actually watch for changes from others done to the world. This is not implemented yet, we only synchronize from server at Start.
• Allow choosing specific asset to add (TCastleComboBox), not random.

Authors and license

Copyright 2024 by Michalis Kamburelis.

Licence: permissive 3-clause BSD license. Basically do what you want, just keep the copyright notice.