https://github.com/raph080/ImGuiHydraEditor

ImGui Hydra Editor is a USD editor written in c++ with the ImGui and OpenUSD frameworks.
https://github.com/raph080/ImGuiHydraEditor

3d-graphics glew glfw hydra imgui opengl openusd

Last synced: 3 months ago
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ImGui Hydra Editor is a USD editor written in c++ with the ImGui and OpenUSD frameworks.

• Host: GitHub
• URL: https://github.com/raph080/ImGuiHydraEditor
• Owner: raph080
• License: mit
• Created: 2023-10-16T04:16:36.000Z (about 2 years ago)
• Default Branch: main
• Last Pushed: 2025-08-09T19:14:37.000Z (5 months ago)
• Last Synced: 2025-08-09T19:28:06.828Z (5 months ago)
• Topics: 3d-graphics, glew, glfw, hydra, imgui, opengl, openusd
• Language: C++
• Homepage:
• Size: 43 MB
• Stars: 115
• Watchers: 6
• Forks: 13
• Open Issues: 4
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

Awesome Lists containing this project

• awesome-openusd - ImGui Hydra Editor - A USD editor written in C++ with the ImGui. (Libraries & Tools / Technical Explanation)

README

          
# ImGui Hydra Editor

ImGui Hydra Editor is a Hydra editor written in c++ with the ImGui and OpenUSD frameworks.

![UI preview of ImGui Hydra Editor](resources/preview_app.png)

This project acts as a playground for USD, and most particularly Hydra 2.0. Therefore, the structure of the application remains simple and contains out of the box examples.

## Building

To build ImGui Hydra Editor, see [BUILDING.md](BUILDING.md) instructions.

## Overview

ImGui Hydra Editor is a tool that processes data using the Hydra 2.0 Framework. Every view from the tool has access to read, insert and author the current state

of Hydra data.

![Views that interact with Hydra data](resources/hydra_data_preview.png)

### Usd Session Layer

From the Usd Session Layer view, the user can type a stage from scratch, add some predefined USD Prim (camera, cube, sphere, ...) or load a USD file and author it. The Usd Session Layer then converts the USD Prims to Hydra Prims and inserts them to Hydra data.

### Outliner

The Outliner view browses all Hydra prims from Hydra data and displays them in a tree view.

### Viewport

The viewport view authors the transforms (translate, rotate, scale) of Hydra Prims. It also creates and inserts a grid to Hydra data.

### Editor

The Editor view allows the user to author the display color of the selected Hydra Prim.

### Engine

The Engine consumes Hydra data with all modifications from the views and generates an image from it.

### Scene Index View

The Scene Index view displays a nodal view of all available Scene Indices loaded into Hydra as well as they connections. This view also authors the **Active Scene Index** when clicking on a node. Hence all views will update its data according to the Active Scene Index.

### Scene Index Attribute

The Scene Index Attribute shows all the Hydra attributes from the selection. Attributes are colored based on their origin:

- ${Inherited \space attribute}$

- ${\color{orange}New \space attribute}$

- ${\color{red}Modified \space value}$

## Scenes Indices

ImGui Hydra Editor implements main concepts of Hydra 2.0 framework out of the box, such as:

* inserting data using [HdSceneIndexBase](https://openusd.org/release/api/class_hd_scene_index_base.html) and UsdImagingStageSceneIndex.

* authoring data via [HdSingleInputFilteringSceneIndexBase](https://openusd.org/release/api/class_hd_single_input_filtering_scene_index_base.html)

* merging multiple data source using [HdMergingSceneIndex](https://openusd.org/release/api/class_hd_merging_scene_index.html)

The views in ImGui Hydra Editor make use of those various types of scene index in order to create the final data to feed to Hydra (Hydra data).

![Scene indices Schema](resources/scene_indices_preview.png)

### HdSceneIndexBase

HdSceneIndexBase is used to insert data to Hydra data.

Examples are:

* UsdImagingStageSceneIndex: used by Usd Session Layer to convert USD data to Hydra data.

* GridSceneIndex: used by Viewport to create and insert a grid to Hydra data.

### HdSingleInputFilteringSceneIndexBase

HdSingleInputFilteringSceneIndexBase is used to filter Hydra data in order to author the Hydra Prim states.

Examples are:

* XformFilterSceneIndex: used by Viewport to author the xform of Hydra Prims.

* ColorFilterSceneIndex: used by Editor to author the display color of Hydra Prims.

### HdMergingSceneIndex

HdMergingSceneIndex is used to merge multiple scene indices together.

Examples are:

* SceneIndexBases: merge multiple inputs (USD prim & grid) to a single output.

* FinalSceneIndex: always contains the scene index with the latest changes.

## Rendering

In order for the render engine to be more flexible, the render is performed using HdRenderIndex, HdEngine and HdxTaskController. See the code for more information.

## Viewport navigation

There is two ways to navigate within the viewport: using the guizmo cube or the mouse and keyboard.

![Viewport navigation](resources/viewport_navigation.gif)

### Guizmo cube

Keep pressing on the guizmo cube and move the mouse to rotate around the focus point. Click on faces/edges/vertices from the cube to change the active camera position accordingly.

Note: guizmo cube navigation is not working properly with z up axis (see [Limitation section](#limitations)).

### Mouse and Keyboard

Here are the shortcuts to navigate using the mouse and the keyboard:

* LMB + Alt: Rotate

* LMB + Shift: Pan

* RMB + Alt or Scroll wheel: Zoom

* F: Focus on selection

* W: Local translate

* E: Local rotate

* R: Local scale

## Additional renderers

Every renderer that implements a hydra render delegate can be used in this project to extends the renderer list.

Here is an example with two different renderers: Storm, Embree.

For your curiosity, here are others: [OpenMoonRay](https://docs.openmoonray.org), [Cycle](https://github.com/blender/cycles) and [Arnold](https://github.com/Autodesk/arnold-usd).

Once the custom render delegates are build, don't forget to set the `PXR_PLUGINPATH_NAME` environment variable before launching the application to make use of them.

![Multi renderers](resources/dual_viewports.png)

## And more

Explore the menu bars of the application and viewports, you may find useful fonctionalities such as:

* Create new USD objects in the scenes (Camera, Cube, ...)

* Profile your Hydra data with Active Scene Index

* Create new views in the main window

* Switch the active camera to the viewport

* Show/Hide the grid

* Show/Hide ambient light, dome light

* Set global/local transform tool

* ...

## Limitations

There is currently some limitations

* ImGuizmo bug: glitchy navigation by using the gizmo cube when the stage up axis is Z (Z up axis is hardcoded in ImGuizmo)

* ImGuizmo bug: guizmo cube not working if multiple viewports and selection is empty

* Instances editing (e.g. translate) is not currently supported

* Single selection

* No Animation

* Simple events (no signal/slot implementation)

* Instanceable not visible in Outliner

* Instanceable cannot be selected (if so selection will switch to parent)

* No Undo

* Grid is on a separate layer at the back

* Does not keep multiple instances of same view when relaunched