> For the complete documentation index, see [llms.txt](https://shaheerxansari.gitbook.io/hydroportdoc/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://shaheerxansari.gitbook.io/hydroportdoc/import-settings.md).

# Import settings

## Import performance: Set options first

{% hint style="success" %}
**Recommended workflow:** Choose all import-related options before importing, then press **Import once**. Repeated reimports can decode samples, rebuild mesh data, and upload geometry again, so adjusting one setting at a time may feel slow with large fluid caches.
{% endhint %}

Most import settings are **not live modifications of an already decoded mesh**. The current source handles some changes specially:

* Selecting a **Source Preset** updates scales.
* Selecting **Velocity Units** updates velocity scaling.
* Switching **Recalculate Smooth Normals** calls `ImportAlembicCache()` when a file path exists.

By contrast, general scale and velocity value changes are not necessarily reflected until the cache is reopened/reimported.

<figure><img src="https://3163553392-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FWkKBDCamr3MmFrohl56q%2Fuploads%2Fx6GVcXBgywVnhI9bonly%2Fimportdetails.png?alt=media&amp;token=52225f7a-1d07-43fe-a991-863365d9ff61" alt=""><figcaption></figcaption></figure>

## Alembic import settings

| Control                        | Default              | Meaning / advice                                                                                                                              |
| ------------------------------ | -------------------- | --------------------------------------------------------------------------------------------------------------------------------------------- |
| **Alembic File Path**          | Empty                | Path to the `.abc` cache. The checked-in source also provides a `Browse...` picker.                                                           |
| **Source Preset**              | Houdini              | Sets default scale conventions for Houdini, Blender, Maya, or keeps user values under Custom.                                                 |
| **Position Scale**             | 100                  | Multiplies source mesh positions into Unreal centimeter-scale coordinates.                                                                    |
| **Recalculate Smooth Normals** | Off                  | Recalculate smooth normals across UV seams. Usually **off for fluids** to preserve provided fluid normals; useful for some cloth-like caches. |
| **Import Velocities**          | On                   | Read usable Alembic velocity vectors when present. Needed for the intended explicit velocity motion-blur path.                                |
| **Velocity Units**             | Scene Units / Second | Selects unit interpretation. May update Velocity Scale.                                                                                       |
| **Velocity Scale**             | 100                  | Converts source velocity vectors into Unreal centimeters/second.                                                                              |

### Source presets

| Preset  |         Position Scale | Velocity Units         |         Velocity Scale |
| ------- | ---------------------: | ---------------------- | ---------------------: |
| Houdini |                    100 | Scene Units / Second   |                    100 |
| Blender |                    100 | Scene Units / Second   |                    100 |
| Maya    |                      1 | Scene Units / Second   |                      1 |
| Custom  | Preserves custom value | Preserves custom value | Preserves custom value |

These are **starting assumptions**, not automatic detection of an exported cache's units. Houdini/Blender presets use a meters-to-centimeters conversion; Maya defaults to centimeter-based values.

### Velocity Units choices

| Choice               | What happens                                                |
| -------------------- | ----------------------------------------------------------- |
| Scene Units / Second | Keeps the source preset's scale or currently entered scale. |
| Meters / Second      | Sets Velocity Scale to 100.                                 |
| Centimeters / Second | Sets Velocity Scale to 1.                                   |
| Custom               | Leaves Velocity Scale for you to edit manually.             |

Formula: `Velocity in Unreal cm/s = Imported Alembic velocity × Velocity Scale` (after the source's coordinate/transform handling).

## Playback controls

| Control                    | Default | Meaning                                                                                                      |
| -------------------------- | ------- | ------------------------------------------------------------------------------------------------------------ |
| **Play Alembic Animation** | Off     | Enables time-driven playback/evaluation; required by the Sequencer evaluation path.                          |
| **Alembic FPS**            | 24      | Sampling rate used for mapping time to cache frames, and for frame displacement in motion-vector generation. |
| **Playback Speed**         | 1       | Playback rate multiplier; negative reverses playback and zero stops time progression.                        |
| **Loop Playback**          | On      | Wraps the playback range instead of stopping at the final frame.                                             |
| **Start Frame**            | 0       | First sample in playback range.                                                                              |
| **End Frame**              | -1      | Last sample in playback range; -1 means use final available sample.                                          |

## Cinematic controls

| Control                 | Default  | Meaning                                                                          |
| ----------------------- | -------- | -------------------------------------------------------------------------------- |
| **Editor Preview Mode** | Disabled | `Disabled`, `Manual Frame`, or `Sequencer`.                                      |
| **Preview Frame**       | 0        | Exact frame shown in Manual Frame mode. Only exposed when that mode is selected. |

## Performance controls

| Control                     | Default | Meaning                                                                                                             |
| --------------------------- | ------- | ------------------------------------------------------------------------------------------------------------------- |
| **Enable Collision**        | Off     | Mesh collision flag; **does not provide animated fluid collision**. Leave disabled for intended fluid VFX workflow. |
| **Enable Performance Logs** | Off     | Logs mesh-upload duration and mesh vertex/triangle counts for diagnosis.                                            |