Spoiler tag

Saturday, July 2, 2022

Creating levels for JSRF - an overview

so for the past few months I have been working on the JSRF level compiler and also an add-on for Blender to export levels for JSRF, also the latest version of the JSRF Mod Tool processes and compiles the data into the game's level file format and boom! custom levels.

Once again huge thanks to Gurten, Daft, Demo, Fuse, Duck from the JSRF Reverse Engineering community & the Cxbx team who made this possible.

This post is an overview of the process,
however I will not be covering the topic of the 3D modelling process since it would be too long to cover, it's a subject on it's own and there's already plenty of tutorials out there for Blender, the focus of this post is on how the JSRF levels work and the tools to create them.

Click here to download the JSRF Mod Tool and the Blender JSRF Stage exporter addon

In this zip file you will find a Blender scene file with a test level, the dev textures for the collision materials, the Blender JSRF Stage Exporter addon an the JSRF ModTool which compiles the level data exported from Blender, and lastly a Mission file which loads when you select "new game", the level will be empty, only corn is standing around, place this file in the "Media\Mission\" folder.


You can find the source code for the JSRF ModTool here




Composition of a JSRF level

A JSRF level is mainly composed of 3D models, of two kinds, one for the visuals that we see and uses textures (top left picture), and another, invisible in-game which is used for the physics simulation(top right pic) and how the player controller interacts with the environment's surfaces.

On the left the visual models, on the right the physics collision model, notice how the collision model has less detail, it's simplified, for instance the stairs become a flat ramp but in the game the yellow surfaces act as stairs and the character takes steps as if there were stairs.
The colors on the surfaces of the physics models help us recognize what type of physics material the faces of the model are assigned.

Lastly, the level also contains curves data for the rails we can grind in-game.

Setting up the Blender JSRF Stage Exporter

First let's install the JSRF Exporter addon for Blender, make sure you have downloaded the files, and have "JSRF_Stage_Exporter.py"

In Blender go to Edit >> Preferences >> Add-ons then
click Install

Browse to and select "JSRF_Stage_exporter.py" and don't forget to tick the checkbox(highlighted in red here) to enable the add-on:

You can the find the JSRF Stage exporter menu at the bottom of the 'Scene' panel:

You will first need to setup the paths as follows:

Stage ID is the name of the stage it will be exported as in the Media\Stage\ directory

Stage Export Path is the folder where the Stage data will be exported

Media Directory should point to the JSRF Media folder

ModTool filepath should point to the JSRF_ModTool.exe

When you press Export Stage, the stage data from blender will be exported, then the JSRF ModTool will run and compile the stage (by default) as the Garage (stg00)

Creating the visual model & using it as a base for the collision

When we start to make a level, we're not going to work on the fancy visuals, instead we roughly model the shape of the level and objects, assigning the physics materials as the default material/texture for the visual models since that's what we're going to use as temporary collision models.

So you'll want to assign the materials that come with the demo scene.

Here's what a test stage looks like:

This is just a test map but that's all you need to know to get started making and testing levels for JSRF, if you're going to do the proper visuals.
You might want to use the old mod tool (download top right) to extract the game's models and textures to re-use them.

Here's what the scene in Blender should look like:

The main "Stage" collection contains "Visual" "Collision" and "GrindPaths", and the those three collections should contain other collections that contain the meshes, and curves for the GrindPaths collection, check how the demo scene is setup if you're not sure.

You must use this structure and naming (except for "Model_group_0" you can name those whatever you like) as that's how the JSRF Stage Exporter addon can process and export the level data.

As for collision models, you can have up to 1023 triangles per collision model group, that's just how the game engine works.

When you have blocked out your level's visual meshes(with the collision materials), as a shortcut you can copy paste the model groups from Visual collection into the Collision collection.
For a finished level the collision models should be modeled separately or you can use part of the visual models as a base, but the models should be simplified as much as possible, for instance, for a set of buildings as collision model, you wouldn't have multiple buildings/boxes for collision, but simply a big wall joining the ground with more or less the same scale as the buildings, in some cases it can be boxes or skewed shapes, in general just try to simplify as much as possible.

The textures must be in .png format and their resolution must be square and of power of two  (i.e: 128x128 or 256x256 or 512x512) the minimum resolution is 8x8 pixels, maximum 2048 (untested), generally recommend sticking to 512x512 as the maximum.

Limitations of JSRF's levels visual models

JSRF Level Visual models only support one UV per vertex, which means you have to treat the model so there aren't multiple UVs per vertex and you need to be very mindful about it, otherwise if you make a complex mesh and once compiled you see it in-game with messed up UVs, it might be tricky(in Blender) to find which part of the mesh is causing the issue.

Ok here's an example (the box in orange) of the issue and how it's solved:

Grind Paths

Grind paths can be created by extracting the edges of a mesh as curves, you then need to add them on the "GrindPaths" collection, inside it's own collection/group.

Also once you're done editing the grind path, make sure to do this for the curve objects:  Object >> Apply >> All transforms
Not ideal, but for now that'll be necessary.

To extract edges as a curve, you can use the following addon, note: in the script change the version from
"blender": (2, 80, 0), to whatever version of Blender you're using so it loads up.
In blender you'll find the button while in Edit mode (edges) right click and at the bottom "Edges to curve"

Note: right now bezier or other types of curves are not supported, or at least I don't know Blender well enough to tell you which type of curves the exporter would support, so try starting from extracting edges as a curve with the add-on I just mentioned, unless you know a way to manually make "curves" that are just point to point without smoothing.

Part 2: to setup and compile the mission file(for custom spray can placement, player spawn location and death warps) see the tutorial on this link