# ogre_slice.cpp

`src/ogre_slice.cpp` implements the `OgreSlice` class and the two `ToOgre()` conversion helpers declared in `ogre_slice.h`.

## Constants

- `kManualObjectPrefix = "ManualObjectSubmap"` — prefix for manual object names.
- `kSubmapSourceMaterialName = "cartographer_ros/Submap"` — the source material defined by `submap.material`.
- `kSubmapMaterialPrefix = "SubmapMaterial"`, `kSubmapTexturePrefix = "SubmapTexture"` — prefixes for per-slice cloned materials and textures.
- `GetSliceIdentifier()` builds a unique `"<trajectory>-<submap>-<slice>"` string used to name the material, texture, and manual object.

## ToOgre helpers

- `ToOgre(Vector3d)` copies x/y/z into an `Ogre::Vector3`.
- `ToOgre(Quaterniond)` copies w/x/y/z into an `Ogre::Quaternion`.

## Constructor

Creates a child scene node under the submap node and a `ManualObject` named after the slice identifier. It clones the source `cartographer_ros/Submap` material per slice, and configures it: no shadow receiving, no lighting, no culling, a depth bias of `(-1, 0)` (pulls the slice toward the camera so it draws over other geometry), and depth writes disabled so submaps blend correctly.

## Destructor

Removes the cloned material and texture from their OGRE managers, then destroys the slice scene node and the manual object.

## Update

Given new `SubmapTexture` data:

1. Positions and orients the slice node from the slice pose.
2. Builds an RGB pixel buffer from the intensity/alpha channels (blue always 0), since OGRE `loadRawData` does not handle RG textures.
3. Rebuilds the manual object as a textured triangle strip quad. The quad is sized from `resolution * width/height`, with the width extending along `-Y` and the height along `-X`.
4. Uploads the pixels with `loadRawData` as a 2D `PF_BYTE_RGB` texture (removing any previous texture).
5. Configures the pass with additive-ish scene blending (`SBF_ONE`, `SBF_ONE_MINUS_SOURCE_ALPHA`) for the pre-multiplied alpha, binds the new texture unit, and disables texture filtering (nearest).

## SetAlpha

Sets the `u_alpha` fragment-program constant on the material, driving opacity of the slice.

## Visibility

`SetVisibility` stores the local flag; `UpdateOgreNodeVisibility(submap_visibility)` makes the node visible only when both the parent submap and this slice are visible.