How to attach mesh to the bone the most efficient way?

Questions
1

My goal is to have animated mesh - lets say human - and put somehing dynamically into its hand. I have tried different approaches but all of them seems to be unnecessarily slow.

My goal is to keep FPS > 100 with 100 animated meshes attached with wearable items

  • The scene has 100 moving animated humans (pretty simple models and skeletons), they are moving around and animating while FPS are in 115 - 120 range (my test phone has 120hz screen).

  1. Create 100 instances of sword (simple) and do nothing with them = FPS 115-120 (no noticeable drop)

  2. Create 100 instances of sword and parent them to the mesh itself = FPS 110 - 115 while swords moving around with meshes (small acceptable drop)

So far so good, but then I wanted to put the sword into model´s hand, I tried following

  1. Create 100 instances of sword and attach them to the hand bone of the mesh = FPS 70-75

  2. Create 100 instances of sword and parent them to the TransformNode that is attached to the hand bone of the mesh = FPS 70-75 (this one was expected)

  3. Create Solid Particle System, make the sword mesh as the particles, create TransformNode attached to the model´s hand and then on sps.setParticles function, I copied absolute position and rotation from the node to the particle. Works as expected but also FPS dropped to like 70 - 75.

In all my approaches that really follows hand (3 - 5), FPS dropped drastically - like 40 FPS drop only for copying position / rotation, it feels wrong considering we are talking about only 100 objects (not thousands or tens of thousands)

Considering that my test phone can render 100 moving animated objects at almost 120FPS, I did not expect any noticeable drop actually.

In attempt nr. 2 - the swords were moving around so position of the mesh is copied to the sword and it did not cause any FPS drop - what is the difference between following mesh and following its bone ? It is just copying one position / rotation data from one object to another, or not ?

Is there some different approach that I may try ? It seems weird that I can render 100 animated meshes and 100 swords perfectly at 110+ FPS (around 40.000 faces) and then only making the sword follow the bone (bone that is already being animated) make 40 FPS drop.

Any ideas ?

Note: In reality I would not need 100 equipped models in the scene at one time, the reason I am going this exagerated way is to idenfity FPS drains like this easily.

Thanx very much !

1 Like
2

I probably solved it - so when someone else run into the same situation, here is the solution, that works as wanted and has like zero impact on performance (which is what I expected from attachToBone in the first place).

    this.handBone.computeWorldMatrix(true);
    const boneMatrix = this.handBone.getWorldMatrix();
    const parentWorldMatrix = this.mesh.getWorldMatrix();

    const localPosition = new Vector3();
    const boneRotationQuaternion = new Quaternion();
    const localScale = new Vector3();
    boneMatrix.decompose(localScale, boneRotationQuaternion, localPosition);

    const parentPosition = new Vector3();
    const parentRotationQuaternion = new Quaternion();
    const parentScale = new Vector3();
    parentWorldMatrix.decompose(parentScale, parentRotationQuaternion, parentPosition);

    const combinedRotation = parentRotationQuaternion.multiply(boneRotationQuaternion);
    const worldPosition = Vector3.TransformCoordinates(localPosition, parentWorldMatrix);

    this.sword.position = worldPosition;
    this.sword.rotationQuaternion = combinedRotation;
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3

I’m attaching the diamond meshes to the bones in this demo:

Here is the rigging part:

4

Why this method does not work: Bones and Skeletons | Babylon.js Documentation

Do we need to fix it?

5

Hello, it DOES work properly as it was in my attemp number 3. The problem was that it caused huge FPS drop (from 115 to 70 in my case), when I do it manually as stated above, I experienced no FPS drop at all.

6

Hi Roland, I looked at your code and if I understood it correctly, you are parenting your meshes to the bone right ? I tried it as well but I got the same FPS drop as I had in attachToBone case.

How many objects are you attaching ? In my case I attached only 1 to every aniamted mesh, and there were 100 such meshes.

7

oh sorry I read quickly!

8

We can easily optimize the function as the most import problem is the call to prepare:

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9

Isnt that prepare called only once ? At the moment when attachToBone is called ? In such case it wouldnt affect FPS permanently if I didnt miss anything here.

10

If it was the case you would not see any perf issue. I need a repro to investigate if you can

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11

1340 non-instanced boxes - I get 120 FPS on Macbook Pro M4 Max

6700 instanced boxes, doNotSyncBoundingInfo set to true - 120 FPS

@stealman Try to turn off bound info syncing of the attached meshes like I did in the second example

12

@stealman In this little game I used thin instances manually ‘attached’ to bones. 13.000 cubes at 300 FPS.

This is the piece of code you might be interested in:

13

@roland Thanx for this - I will try this doNotSyncBoundingInfo = true It might help actually ! In the meantime I came to conclusion, that “manually attached thin instances” as you named it, is the way to go. Tried it yesterday and it is blazing fast !

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14

Would you please mark my answer as the solution in this case? Thanks! :handshake: :wink:

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15

Done :wink:

That being said I would love to see a PG showing perf regression with the core attachToBone function

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16

As you can see it performs well.

17

Sorry for the offtop.
Do You know guys why in this example mesh selection is taking so much time?

image
image1300×1247 141 KB

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18
2 Likes
19

You can merge the meshes:

image
image596×212 27 KB