Modular pipes with FitOnLine

This guide builds a modular pipe SmartProp in Counter-Strike 2 using FitOnLine, BendDeformer, CreateSizer, CreateRotator, and nested SmartProps.

📦 Download Pipe Mesh Kit (pipe_meshes.zip) 📦 Download Finished guide_fitonline.vsmart

note

This guide builds on the fundamentals in the SmartProps guide. Start there when working with SmartProps for the first time.

Mesh requirements and preparation

Before building a procedural pipe system, the source 3D meshes must be prepared according to specific guidelines:

1. Pivot Placement: Place the origin pivot at the start or end border of the mesh along the connection axis, such as Z or Y.

   

2. Subdivision Density for Bending: Straight pipe sections only need a few longitudinal segments. Meshes intended for curvature or deformation require extra edge loops along their length so they deform smoothly when passed through BendDeformer.

   

3. Grid-Aligned Sizing: Use predictable unit lengths such as 32, 64, 128, or 192 units. These values keep the length and selection criteria calculations direct.

   

tip

Consistent Alignment Axis

Align all pipe meshes along the same primary axis (for example, Z-up) with matching cross-sectional diameters.

This tutorial uses a custom modular pipe kit built in Blender:

Prepare the models

Each pipe piece has to exist as a compiled .vmdl before a SmartProp can place it.

1. Place the unpacked FBX files in the addon's content directory, such as content/csgo_addons/<addon>/models/pipe_kit/.
2. Create a .vmdl for each mesh.
3. Compile the models in the Counter-Strike 2 tools.

tip

Configuring each .vmdl by hand is slow for a kit this size. Hammer 5 Tools batch-generates and synchronizes the whole set from one reference asset, see AssetGroup Maker.

Set up FitOnLine

FitOnLine places child elements sequentially along a line vector according to each child's LinearLength selection criteria.

1. Create a new SmartProp document and save it (e.g., models/pipe_kit/guide_fitonline.vsmart).

2. Import all .vmdl files into the SmartProp hierarchy. Hammer 5 Tools has a Bulk Model Importer for this:

   • Right-click in the Hierarchy window and select Bulk Model Importer.
   • Select all the pipe .vmdl files.
   • Check Create ref element and click OK.

   

3. Move all models except pipe_01_64_a into a temporary group and disable that group to focus on the base piece:

   

Configure length and selection criteria

4. In the root FitOnLine element, set the End coordinate to (0, 0, 128).

5. On the pipe_01_64_a model element, add a Selection Criteria: LinearLength modifier and set Length to 64.

   

6. Place the SmartProp in Hammer to test it. Because the FitOnLine length is 128 and each pipe segment is 64, exactly 2 segments are placed:

   

Add an interactive sizer handle (CreateSizer)

7. Create a new Group element and attach a CreateSizer modifier to it.

tip

Modifier Grouping Best Practice

Placing CreateSizer in an empty parent group keeps the hierarchy clean and prevents sizer transforms from unexpectedly shifting the local coordinate origin of the child FitOnLine element.

8. Create a float variable named SizerLengthZ (uncheck Show in editor).

9. In the CreateSizer modifier:

   • Set Output Variable Max Z to SizerLengthZ.
   • Set Initial Min Z to 0 and Initial Max Z to 128.
   • Set Constraint Min Z to 0 and Constraint Max Z to 512.

   

   

tip

Setting Sizer Constraints

Always configure Constraint Min Z and Constraint Max Z on the CreateSizer modifier to prevent accidental inversion or excessive stretching.

10. In the FitOnLine element, change the End.Z property from constant 128 to the SizerLengthZ variable.

11. In the Hammer viewport (Shift + S), drag the sizer arrow handle to dynamically lengthen the pipe:

    

Smooth scaling and material UV compensation

To prevent stepped gaps between fixed-size meshes, enable dynamic scaling:

12. In the FitOnLine element, set Scale Mode to SCALE_END_TO_FIT (or SCALE_MAXIMIZE).
13. Select the model element, switch its Model Scale (Z) field to Expression, and enter:

    LinearScale()

note

What does LinearScale() do?

The LinearScale() expression returns the scale multiplier used by FitOnLine to fill the remaining span. Reference it to offset child caps or connectors by the scaled dimensions.

14. In the model's Selection Criteria: LinearLength, set Allow Scale to true, Min Length to 64, and Max Length to 192.

    

15. To prevent stretched textures when scaling pipes, enable UV scaling in the Source 2 material (.vmat):

    • In Material Editor, enable Scale TexCoord U By Model Scale Axis and set it to UV.u * model.z.

    

16. Adding End Caps:

    • Wrap the pipe model in a group (Ctrl + G) and move the LinearLength criteria to the group.
    • Add a PickOne element containing cap models (end_a, end_b) set to selection mode FIRST.
    • Add a Translate modifier to the cap group with Translate.Z set to LinearScale() * 64.

    

Branch with nested SmartProps

To allow pipes to branch and change direction, nest the SmartProp inside itself.

1. Create a PickOne element named End.

2. Place the Cap PickOne and connector meshes (pipe_01_32_a, pipe_01_32_b) under End.

3. Move the translation and a CreateRotator modifier to the End PickOne element.

   

4. Self-Referencing SmartProp:

   • Add a SmartProp element under the End PickOne.
   • Set its SmartProp path to the current .vsmart file itself.

warning

Preventing Infinite Recursion

When creating self-referencing SmartProps, always set the parent PickOne selection mode to FIRST and ensure a non-recursive terminator (like a closed cap) is the first item. Setting the selection mode to RANDOM will cause the SmartProp to spawn endless recursive copies upon placement, causing the editor to freeze.

5. Customize handle shapes, colors, and offset positions for the PickOne widgets:

   

6. Configuring Branch Connectors:

   • Create a group for pipe_01_32_b (call it 32_b).
   • Duplicate the SmartProp reference element into the 32_b group.
   • Use viewport isolation (Ctrl + H) to precisely position and rotate the nested SmartProp handle to align with the branch outlet of the connector mesh.

   

7. Repeat the same setup for 90-degree corner connectors (pipe_01_crn_a and pipe_01_crn_b):

   

Create curved pipes with BendDeformer

This section introduces the BendDeformer element for smooth curved bends in Hammer.

1. Duplicate the FitOnLine structure and place it in a new group named Bend.

2. Wrap the model in a BendDeformer element inside the Bend group.

3. Attach a CreateRotator modifier to the Bend group:

   • Set Apply To Current Transform to false.
   • Set Coordinate Space to Element.
   • Set Rotation Axis to (1, 0, 0).
   • Create a float variable named BendAngle and bind it to Output Variable.
   • Enable Enforce Limits with Min Angle = -90° and Max Angle = 90°.

   

tip

Enforcing Angle Limits

Always check Enforce Limits on the CreateRotator (Min = -90°, Max = 90°) to prevent accidental, non-physical inversions.

4. Reorganize and clean up the hierarchy:

   • Move the main picker and sizer handles to the top level.
   • Ensure sizer constraints on Z are properly bounded (e.g. Constraint Max Z = 192).

   

5. Configuring BendDeformer:

   • In Bend Angle, bind the BendAngle variable.
   • In Angles, set (-90, 0, 0).
   • Set Size.X to SizerLengthZ (with Y and Z set to 0).
   • Set Bend Radius to SizerLengthZ when the bend radius should follow the current pipe length.

   

Rigid deformation modifier

warning

Why is Rigid Deformation required?

When child elements (such as PickOne handles or nested SmartProp instances) sit inside a BendDeformer, the deformation skews their interactive viewport widgets and the widgets stop appearing in the viewport.

Attach a Rigid Deformation modifier to each control group. It exempts that group from the deformation, so its viewport widgets keep working while the mesh geometry underneath still curves.

Final result and workflow recap

The result is a procedural pipe SmartProp ready for testing in Hammer.