Great to hear, JC!
Transformation of coordinate systems is something we all have to live
with when converting from 3D modeling tools and physics engines to game
engines.
One question I have, when you transfer "low level mesh data" from Chrono
to Unreal, do you also have a method of caching that so you can send it
to the GPU once (and not every frame)?
In any case, it's nice to hear your project is coming along nicely, good
luck with it!
Greetings, Marcel
On 03-Aug-23 7:06, 'JC Denton' via ProjectChrono wrote:
Thanks Marcel!
I do indeed have my physics thread separate from my render thread. I
have a queued callback system to send render debug info from
my chrono dll to the unreal side in a thread safe manner.
I rolled my own debug helper class to manually loop through the
vertices from ChCylinder and ChTriangleMeshes and
push those into vert structures that Unreal can read. Seems to be
rendering the meshes in unreal okay, just gotta work out some
transform conversions now
and expand it to other chrono shape types.
I just pulled the vert data directly from the m_trimesh_shape which
exists inside ChWheel already.
So now I have my Unreal visual meshes driven from the Chrono physics
output + the chrono collision debug shapes rendering overlayed on top
for comparison which is exactly
what I was looking for.
Thanks!
-JC
On Wednesday, August 2, 2023 at 12:11:41 AM UTC-7
[email protected] wrote:
Hello JC,
Responses in-line below.
On 02-Aug-23 5:27, 'JC Denton' via ProjectChrono wrote:
> I do indeed visualize my wheels and chassis no problem in Unreal
> engine, however my visual mesh in Unreal is not the same as the
> collision meshes in Chrono. I would like to draw the scene as
Chrono
> sees it,
> to ensure it aligns 1:1 with what Unreal sees.
Understood, and this of course is a generic "issue". Collision meshes
are always simplified meshes to keep a decent performance and the
visual
mesh (regardless of Unreal, Irrlicht or VSG rendering it) will be
different. I typically use a mental model where I distinguish
three worlds:
1. The visual one, that is normally rendered.
2. The collision world, that has all kinds of collidable (simple)
shapes
bumping into each other (car bodies bumping into terrain or other
cars).
3. The tire world, that typically uses its own type of collision
system
(although that depends a bit on the type of tire, I mostly use
semi-empirical ones for my use case.
> Hoping there is a way (ideally without modifying Chrono engine
code)
> to visualize the contact points, tire, wheel etc.
I've gone through a similar process and with the help of this
community
and a few small patches I have mostly managed to get to the data I
want
to visualize without having to change the engine. I did end up
doing a
lot of the drawing "myself". There is a lot of information
available at
the end of every physics "step" so the biggest deal then becomes
how to
pass all that data to (in your case) Unreal. Part of that design
is also
about potentially decoupling the physics thread from your
rendering (at
least in my case I quickly concluded that with physics running at
1000
fps my graphics card was never going to keep up).
> I notice inside ChWheel::AddVisualizationAssets() we have some
logic
> to setup triangle meshes:
>
> void ChWheel::AddVisualizationAssets(VisualizationType vis)
> {
> if (vis == VisualizationType::MESH &&
!m_vis_mesh_file.empty()) {
> ChQuaternion<> rot = (m_side == VehicleSide::LEFT) ?
> Q_from_AngZ(0) : Q_from_AngZ(CH_C_PI);
> auto trimesh =
>
geometry::ChTriangleMeshConnected::CreateFromWavefrontFile(vehicle::GetDataFile(m_vis_mesh_file),
> true, true);
> m_trimesh_shape =
> chrono_types::make_shared<ChTriangleMeshShape>();
> m_trimesh_shape->SetMesh(trimesh);
> m_trimesh_shape->SetName(filesystem::path(m_vis_mesh_file).stem());
> m_trimesh_shape->SetMutable(false);
> m_spindle->AddVisualShape(m_trimesh_shape,
> ChFrame<>(ChVector<>(0, m_offset, 0), ChMatrix33<>(rot)));
> return;
> }
> }
>
> Is there an easy general way to draw arbitrary chrono shapes
such as
> ChTriangleMeshConnected or ChCylinderShape? Or do I need to roll my
> own function to iterate over each chrono shape's verts and then
render
> them on my Unreal side?
I don't think there is. For "primitive" shapes I ended up
implementing
them myself based on the provided parameters and I mostly use
those to
visualize how the vehicle physics respond. For "mesh" shapes I
ended up
completely ignoring what is defined in Chrono and loading my own 3D
model, using a bit of glue code to make the right parts of that model
show up in the places calculated by Chrono (position and
orientation).
You could also take the defined OBJ meshes and load those in Unreal I
guess. OBJ is nice because it's a simple format to generate and
parse.
That said, I ended up wanting to have the whole vehicle in a single
graphics file, so I ended up with a GLTF file containing all the
parts
(body, wheels, etc.).
Greetings, Marcel
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