SlicerLayerDisplayableManager

A 3D Slicer module introducing a new displayable manager architecture for layered rendering and interaction handling.

Usage

The API Reference documentation provides API-level documentation.

Overview

SlicerLayerDisplayableManager is a module designed to simplify the integration of new display pipelines in 3D Slicer. It introduces a flexible and extensible framework for managing layered rendering, interaction forwarding, and camera synchronization across multiple pipelines.

This module aims to address common limitations in existing displayable managers by offering a more modular and injectable design.

Goals

• Factorize pipeline creation and teardown
• Enable layered rendering and interaction forwarding
• Maintain focus continuity across pipelines
• Synchronize cameras across views and layers
• Centralize render request handling

Limitations in Current Displayable Managers

The current displayable manager (DM) architecture in 3D Slicer presents several structural and usability limitations:

• Redundant logic: Each DM reimplements pipeline instantiation and renderer setup independently.
• Custom camera sync: Camera synchronization strategies are manually implemented per DM, leading to inconsistent behavior.
• Complexity growth: DMs tend to accumulate unrelated logic over time, making them harder to maintain and extend.
• Focus handling: Focus decisions are based on proximity to interaction only, without consideration for layer priority.
• Factory instantiation: DMs are created using string-based factories, preventing injection of shared dependencies or services.

Improvements Introduced by SlicerLayerDisplayableManager

The module introduces a new architecture to improve development quality and scalability for visualization widgets:

• Centralized pipeline management: Pipelines are automatically created and deleted by the displayable manager.
• Dependency injection: Lambda and callback-based creators allow find pipeline creation control and injection of shared logic at pipeline creation.
• Modular camera synchronization: A dedicated synchronizer handles camera updates across views and layers for pipelines following the main camera.
• Layer-aware interaction: Pipelines declare their render layer with arbitrary values, enabling prioritized focus and interaction handling without handling the finer grained VTK logic.
• Python integration: A Python abstract class enables rapid development and integration of pipelines.

These changes simplify the development of new widgets, reduce boilerplate, and improve maintainability of existing visualization components.

Key Features

• Pipeline registration via factory and creator API
• Lambda and callback support for dependency injection
• Customizable observer update pattern
• First-class Python abstract pipeline class

For more information on the extension's architecture, please refer to the online documentation.

Installing the extension

The extension can be installed through the extension manager from 3D Slicer 5.10 onwards:

Getting Started

To use this extension checkout the getting started documentation.

And refer to the examples.

Testing

Tests are split between the two projects:

• LayerDM is covered by unittests that only require the LayerDM runtime wheel. They are run by the 3D Slicer test runner when testing the extension, and by pytest when testing the wheels.
• LayerDMSDK is covered by a test that builds a third party package against the SDK. Requiring the SDK, it belongs to the SDK test suite and is out of the scope of the LayerDM unittests.

To run them against the wheels, install the slicer-layer-dm wheel (and its dependencies) in a Python environment, then:

# LayerDM unittests (runtime wheel only)
python -m pytest LayerDM

# LayerDMSDK tests (require the SDK wheel)
python -m pytest LayerDMSDK

Note: LayerDM/Testing/Python drives displayable managers in render windows and renders offscreen. No X server is required: with no DISPLAY, VTK falls back to the EGL backend and renders with software GL. A display is only used if one is already available.