Car modeling tips and remarks.
Todo: Renew screenshots ` is much easier.
There are already pretty good car models, available on sketchfab or blendswap.
See our forum topic, new post, old post shows the list of cars.
Some are too high poly or too low. And some just don't fit the game.
The license for the art must be GPL, CC-BY-SA, CC-BY, CC0, etc so we could use it.
Models sometimes still require some work (to have in game):
- Lowering polygon count. No subdivisions. Decimate if necessary.
- UV unwrap and mapping various car parts to texture parts.
- Making interior (if not present). Texturing.
- Baking AO maps
Models meant for rendering (not games) need these steps.
The more of these are needed to be done, the less likely a vehicle will be in SR.
We are using and recommend Blender to do all of the modeling tasks.
At least basic knowledge of Blender is required.
There are several good resources on internet to learn it:
- Blender Manual. Only few chapters are useful, Introduction, Modeling, and Texturing/Unwrapping.
- Blender Tutorials video playlist
- other video tutorial series
- Basically any common task in Blender is shown on some video (e.g. search youtube). Keep in mind the version used should be close to yours and recent.
- There are also video tutorials specifically on car modeling.
Various websites with Blender key shorcuts: katsbits, keyxl.
Some main, quite useful key shortcuts:
- 1
- Tab - toggle edit mesh mode, Ctrl Space - zoom toggle
- ` - quick change view, T - toolbox, N - transform, view details
- Select: A - all, B - rectangle, C - circle, Ctrl I - Invert
- 2
- G - grab, Move, S - Scale, R - Rotate
- then can press X,Y,Z for axis, and type numerical values*
- Ctrl A - Apply e.g. all transforms before export
- H - Hide selected, Alt H - unhide all
- G - grab, Move, S - Scale, R - Rotate
- 3
- U - Unwrap, with options
- P - Separate (e.g. faces), Ctrl J - Join meshes
- Shift D - Duplicate*, Ctrl M - Mirror*
- 4
- Alt N - Normals (for e.g. Flip or Recalculate outside).
- E - Extrude (e.g. edge or face), K - Knife tool
- F - add face(s) (needs at least 3 vertices or 2 edges selected)
- M - Merge vertices
- Subdivide (faces), Bevel (edges)
Useful modifiers:
- Decimate - reduce if too high poly
- Subdivision surface - if too low poly
- Edge split - for hard edges
- Mirror, Boolean, Array, Curve
Things to keep in mind when modeling (required by game):
Keep resonable triangles count (faces, polygons).
You can see it in top bar in Blender (turn on Statistics in viewport Overlays).
For a very good looking car for game, total of 50k to 150k triangles would be required (not counting wheels, k is 1000).
Generally the less triangles a model has, the more detail has to be on textures.
One wheel (including brake disc and caliper) should be about 4k to 10k triangles.
Comments section has more info.
More detail can (and should) be put in textures. More triangles will unnecessary reduce game Fps.
Ambient Occlusion (AO) is easy to bake and gives good feeling.
Very recommended (even required) for all parts: body, interior, wheel.
Baking Normal map is usually difficult and time consuming, when generated from high poly model.
It is not required, but great if already present with model.
Split View to add new of type Shader Editor.
Switch it to: World and
from its menu: Add - Texture node - Image texture
In new appeared block click button + New,
name it e.g. AO, and set to 1024 size.
On right in Render properties (camera icon) change engine to Cycles.
now under Bake pane, set Bake Type to Ambient Occlusion
set margin to 2 px (or more).
Switch a view to UV Editor (or switch to UV Editing on top).
From its menu Image click New, set size to 1024, name it e.g. AO2.
Finally press Bake, back under Render properties.
If you see any errors, make sure material has texture.
Then rendering AO should start and appear on texture.
After many seconds pass when it's done,
click menu Image and Save as, to save AO texture for game.
Make as much detail as possible, but check out other cars.
HI and BE models are newest and best here, have lot of detail in textures. BE has even more, baked in normal map.
To check geometry (triangles) just start game and press F10 to toggle wireframe.
Also game logs car meshes info in ogre.log (how to find it in Paths wiki.
Look for "MESH info: " it says how many submeshes (subs, materials) and how many triangles (tris) each part has and the total amounts.
Most optimal and preferred is when there is 1 submesh and 1 material in each .mesh file.
Keep in mind that faces in blender can be two sided, but in game are one sided.
Thus the face normals (in blender) must be flipped to proper side. They won't be visible in game if on the other side.
Cars (just like tracks) aren't big in size.
ES is biggest and after export the Ogre, all .mesh files are about 1MB, and all textures 5MB.
It's best to keep the size not too far from that (current highest are: 6MB meshes and 19MB textures).
We have git repository with .blend files for most SR vehicles
https://github.com/stuntrally/blendfiles/tree/master/cars
Good example is the new HI model, was almost ready for game.
ES had high poly model and baking normalmap (bad, not used) and ambient occlusion was done for it.
S8 and XZ are okay, but they had a simple unwrap and interior made.
Note: replace ES with the in-game car name you work with.
Name the body parts (and the geometries): ES_body, ES_interior, ES_glass.
If you have a wheel then use: ES_wheel. ES_brake for brake disc and caliper (not necessary).
Car gets exported to such meshes:
- ES_body - this is car body, only 1 material, covering the metal parts that will be colored in game using car color. Don't include any geometry here that doesn't have car paint on it in Blender.
- ES_glass - this is car glass (windows) and also can have front or rear lights glass (makes lights look better).
- ES_interior - has not only interior (seats and all inside car stuff) but also front/rear lights, exhaust pipe, car bottom, rubber (dark) parts between car metail and so on. Simply all model parts that don't get colored by car paint.
- ES_wheel - car wheel rim (metal) and car tire, may also have brake disc. It is best to use 1 material, and put parts in in different places (UV) of texture.
- ES_brake - (optional)
This makes the exported files already named properly for game, so just copying there works.
(We use such short names, simply because it is not possible to use original car names).
This Blender screenshot shows (for XZ car):
- 3D view of interior faces
- joined geometry parts with good names
- material names, still too many
- UV editor with unwrapped faces to texture
(note this is a work in progress, only interior and car bottom are mapped properly, rest is moslty garbage, not done yet)
A finished interior with good UV map would look similar to this (for ES car):
Exporting models from Blender to Ogre (see Objects Wiki on how to install exporter) is done from menu File|Export|Ogre3D.
From the exporter options pick axes as "xz-y", use tangents (mark checked), uncheck edges-list (we don't need them).
If succesfull, you will find files in the selected folder (1 mesh file in xml format and 1 binary mesh fie) for each selected geometry in blender.
Copy the binary .mesh files (parts) into the data/cars/ES dir in Stunt Rally (replacing the older/original ones).
Start Stunt Rally and check how it looks.
Name all materials in Blender with car prefix, e.g. ES_body, ES_glass, ES_interior, ES_wheel, etc.
Keep the material count at minimum. This is crucial.
We can't have each car part like front/rear lamps, seats, steering wheel etc as separate parts, they must be on 1 mesh (geometry) and have UV mapped to different parts of texture.
It is best to have each body part with 1 material, with the same name as geometry (ES_interior, ES_glass etc).
(Each material represents new batch (draw call) and parameter changes which reduces game Fps).
So, join (Ctrl-J) all geometry in interior. Mark seams on edges that will get cut. Unwrap (U) parts.
Use UV editor to move and scale parts to according places on texture. Don't make parts overlap on texture.
Use bigger scale for parts that require more texturing (detail).
In game we can use:
- diffuse map - to add texture to objects, change color, etc. This is required, but it can be simple 1 color at start.
- specular map - if parts have different shininess (color in rgb and power in alpha), e.g. this is obvious for wheel rim (shiny) and tire (matte), still can be on 1 texture which is more optimal (more Fps).
- reflection map - to mark shiny parts with environment reflection (eg. glass, rim), or deny reflections (tire)
Desired file structure in data/cars/3S (for already exported car 3S).
3S_body.mesh
3S_interior.mesh
3S_glass.mesh
3S_wheel.mesh
3S_brake.mesh
Those files were already described.
about.txt - Contains info of the model, credits, changes.
description.txt - This text file contains the info text which is displayed in game. It has general info about the car and how it handles in game.
engine.wav - The engine sound file (at 7000 rpm). Must be wav and 44100 Hz, mono or stereo 16-bit.
3S_body00_red.png - Main body texture. It has to be colored in saturated red, because it will change depending on car paint chosen in game. Can just be whole red texture at start of car creation.
3S_body00_add.png - Old version cars used this to add detail to red texture. Can be full transparent at start.
Old, not: 3S_body00_brake.png - Same as add but with rear brakes lit. The texture add is replaced to brake when car brake is on.
3S_interior.png - interior texture (with various car parts mapped too) possibly with 3S_interior_normal.jpg.
3S_glass.png - the transparent glass texture (usually small)
optional: 3S_spec.png, 3S_refl.png - to map specular parts and reflection, or deny them on matte parts.
3S_Tire.png, 3S_Tire_norm.png - diffuse and normal texture for tire model
More details in Materials page.
Materials for all cars are defined in data/materials/cars.mat
A very basic example for 3S (replace with your new), you can comment out lines with %%//%%.
hlms car_body_3S pbs : car_body
{
specular_map 3S_spec.png
}
hlms 3S_glass pbs : car_glass2
{
}
hlms 3S_interior pbs : car_interior
{
diffuse_map 3S_interior.png
}
hlms 3S_wheel pbs : car_wheel
{
diffuse_map 3S_wheel.png
}
More complicated example for 3S wheel
hlms 3S_wheel pbs : car_wheel
{
diffuse_map 3S_wheel.png
normal_map 3S_wheel_norm.jpg
specular_map 3S_wheel_spec.png
roughness_map 3S_wheel_rough.png
}
Another for XZ wheel
hlms XZ_wheel_chrome pbs : car_base
{
diffuse_map XZ_Tire.png
diffuse 0.1 0.1 0.1
specular 1.0 1.0 1.0
fresnel_coeff 0.6 0.6 0.15
roughness 0.1
reflect yes
}
No car is perfect, and every one has some smaller or bigger issues.
I describe some here, with what could be done to improve.
We are open for artists who could improve cars (use Forum to contact us if you want to help).
The ALL (total) counts are computed as sum of body, interior, glass and 4 times wheel and brake.
ES was great long ago, but recent HI or BE models have surpassed it.
They have baked detail from high poly models into textures (and normal maps).
Usually models meant for PBS have even big 4k textures and more than we need (or can have in Ogre 1.x).
ES had okay dashboard too, so good it could actually be used for in car camera view.
Brake.mesh tri count is too high (could use Decimate).
You can see that lines in wireframe aren't dense for body.
ES_body.mesh sub: 1 tri: 19.0k
ES_interior.mesh sub: 1 tri: 38.0k
ES_glass.mesh sub: 1 tri: 1.0k
ES_wheel.mesh sub: 1 tri: 4.1k
ES_brake.mesh sub: 1 tri: 3.1k
ES ALL sub: 11 tri: 86.9k
S8 has higher tri counts, but not much detail in textures. Hard to improve, has to be made by an experienced artist.
S8_body.mesh sub: 1 tri: 43.0k
S8_interior.mesh sub: 2 tri: 81.1k
S8_glass.mesh sub: 1 tri: 16.6k
S8_wheel.mesh sub: 1 tri: 3.9k
S8_brake.mesh sub: 1 tri: 3.1k
S8_wheel.mesh sub: 1 tri: 3.9k
S8 ALL sub: 12 tri: 168.9k
This car has very smooth body, but nowadays with too low tri count.
Interior was made by me and thus is rather poor. I copied seats from S8, and made the rest of interior by extruding 1 line and adjusting it. It has also poor texturing there.
But still it's an interior and better than none (the original model didn't have it).
Next thing is that the body has holes. They are visible from close. It is needed to add triangles to interior which would be dark and would cover those holes. Interior also has holes, near mirrors, when seen from inside car. Need to add more interior faces there.
This happens because faces are 1 sided in game. When adding the second, interior faces, keep some distance, because if it's too low, shadows are blinking on those parts.
Wheel rim has too many tris (about 2x more). But I left it since too much decimation can produce unwanted distortion in mesh.
XZ_body.mesh sub: 1 tri: 22.0k
XZ_interior.mesh sub: 1 tri: 20.1k
XZ_glass.mesh sub: 1 tri: 1.0k
XZ_wheel.mesh sub: 1 tri: 11.8k
XZ_brake.mesh sub: 1 tri: 0.3k
XZ_wheel.mesh sub: 1 tri: 11.8k
XZ ALL sub: 11 tri: 91.8k
