Implement section caps through sceneModelEntity:capMaterial

[ijlal99]

Please give this branch a test and let me know if you see any bugs so that we can fix it before merging into main.

[paireks]

Ok, I will give it a try :)

[paireks]

Hey guys, I'm testing it on various different models, it works better than I thought. It runs quite fast and gets quite good results. But also it has some limitations:

• models have to have all meshes closed (solids). But in reality many models have none of them closed or only some of them closed, which results in only partial caps / no caps.
• for huge models (such as WestRiverSideHospital) it crashes my browser.
• it doesn't work once I set the position of the model (it doesn't cap then)
• I think it would be good to check the model far from origin, but I can't remember which one was it. Do you remember @xeolabs?

Because of the above I'm thinking if maybe it would be better to add this functionality more as an example rather than a xeokit-sdk functionality? What do you guys think?

[ijlal99]

Hi @paireks!

Thank you for trying out this feature and your valuable feedback.

1. For the capping of only solid objects, this is not really a limitation but actually a requirement that we only hatch solid objects.

   xeokit-sdk/src/viewer/scene/sectionCaps/SectionCaps.js

   Line 201 in d324265

   if (isSolid && object.capMaterial) {

2. For huge models like WestRiverSideHospital, I checked and the browser crashes even when the SectionCaps are disabled.
3. We currently do not have any event in xeokit that informs us that the position of an object has been changed. We plan to handle this situation later.
4. Our first implementation of this feature was a plugin and then we switched and made it a part of xeokit sdk with the agreement of @MichalDybizbanskiCreoox and @xeolabs.

[MichalDybizbanskiCreoox]

2. For huge models like WestRiverSideHospital, I checked and the browser crashes even when the SectionCaps are disabled.

I've added a section plane and capMaterials to the xkt_dtx_WestRiverSideHospital.html example (also calling Viewer constructor with the readableGeometryEnabled: true flag needed for hatching).
The example works for me in Chrome on macOS just fine:
https://github.com/user-attachments/assets/9dfe8b42-c5a3-4c7e-baa5-ecc133d5355b

[MichalDybizbanskiCreoox]

When the immediate addCapsMaterialsToAllObjects(...) call is removed, and instead called after the model loads (from e.g. a test function window.addHatching = () => addCapsMaterialsToAllObjects(...);) the hatching doesn't appear.

[xeolabs]

The .layer attribute is actually private within a SceneMesh, so let's not access that - rather, please add a get primitive accessor to SceneMesh, and then test if the mesh is solid with object.meshes[0].primitive === "solid"

[MichalDybizbanskiCreoox]

A primitive has different semantics throughout the system.
Some places consider it as e.g. solid or surface (SceneModelMesh), while others consider it as e.g. triangle-strip or line-loop (ReadableGeometry).
Perhaps it'd be clearer, if the SceneModelMesh exposed a isSolid() predicate, instead of a confusing primitive property?

[xeolabs]

Rename key->objectId

[xeolabs]

Rename value->modelId

[xeolabs]

I have one architectural change request:

• add a boolean Entity.capped property, which would indicate if that Entity is currently capped
• add a Scene.crossSections.capMaterial property, which is a Material
• then make Entity.capMaterial point to Scene.crossSections.capMaterial unless overridden by a user's Material instance

This way, we're also consistent with selection, highlighting etc.

[MichalDybizbanskiCreoox]

At the moment semantics of not assigning capMaterial are: "don't create section caps for this entity", which is useful for users that are not interested in hatching, and so don't have to pay the performance price for the feature.
It's also as simple as a single line of code to apply any global/default capMaterial to all entities.

[xeolabs]

Need a class comment - maybe something similar to SAO