ImGui Hydra Editor

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

This project acts as a playground for USD, and most particularly Hydra. Therefore, the structure of the application remains simple and not over-engineered.

Supported platforms

ImGui Hydra Editor was primarily developed on MacOS (Ventura 13.6) but was also built and tested on Linux (Centos 7).

Dependencies

Required:

• gcc compiler
• cmake v3.27 or newer
• OpenUSD v23.08 or newer

Embedded:

• glew
• glfw v3.3.8
• imgui v1.89.9
• ImGuizmo v1.83
• ImGuiFileDialog v0.6.5
• ImGuiColorTextEdit

Documentation

For more information about the code, please check the header files.

Getting Started

Install dependencies

Make sure gcc and cmake are installed

gcc --version
cmake --version

If some version and info are printed after running the previous commands, gcc and cmake are installed. If you get command not found error, please be sure to install them first.

Download OpenUSD

The easy way to get a pre-built version of USD is to download the one from the Nvidia website.

To build USD manually, go to the OpenUSD release page, download the last release available and build it (build info in the OpenUSD README.md).

Don't forget to add the --embree flag to the build command if you wish to have access to the Embree renderer from ImGui Hydra Editor.

python3 USD/build_scripts/build_usd.py --embree /path/to/install

Clone ImGuiHydraEditor

Clone the git project using the following command:

git clone --recurse-submodules https://github.com/raph080/ImGuiHydraEditor.git

The recursive flag will automatically include the following projects: glew, glfw, imgui, ImGuiColorTextEdit, ImGuiFileDialog, ImGuizmo

Build ImGuiHydraEditor

Within the cloned ImGuiHydraEditor, create a build folder and run cmake from this newly created folder by specifying the root path to OpenUSD build:

mkdir build
cd build
cmake -Dpxr_DIR=/path/to/OpenUSD/build/folder -DCMAKE_INSTALL_PREFIX=/path/to/install/folder ..
make
make install

Run ImGuiHydraEditor

if everything went well, 3 new folders are created in your /path/to/install/folder: bin, include and lib.

You can then run the ImGuiHydraEditor application as follow:

Linux:

export LD_LIBRARY_PATH=/path/to/OpenUSD/build/folder/lib:/path/to/OpenUSD/build/folder/lib64:$LD_LIBRARY_PATH
./ImGuiHydraEditor

MacOS:

export DYLD_LIBRARY_PATH=/path/to/OpenUSD/build/folder/lib:$DYLD_LIBRARY_PATH
./ImGuiHydraEditor

You can optionally load a USD file directly using the following command:

./ImGuiHydraEditor /input/file.usd

Viewport navigation

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

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).

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 of 4 different renderers: Storm, Embree, Cycle and Arnold.

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.

And more

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

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

Next steps

Here are the next steps that are planned in order to improve the tool and discover more about Hydra:

• Switch from UsdImagingGLEngine to HdEngine or HdxTaskController
  • Allows multiple scene delegates
  • Add the grid dynamically to the RenderIndex
  • Abstract the Model to Hydra Objects (not USD object anymore)