Source code and study data for the TOG 2021 paper: Mid-Air Drawing of Curves on Surfaces in Virtual Reality.

For a barebones demo of our Mimicry technique, try out the pre-built demo: https://github.com/rarora7777/curve-on-surface-drawing-vr/releases/tag/v0.1. Downloading the building the code yourself allows for much greater testing freedom, and is therefore highly recommended.

To try out the user study for yourself, download the study executable: https://github.com/rarora7777/curve-on-surface-drawing-vr/releases/tag/StudyExecutable.

To download the raw data from our user study and code to read and analyze the data: https://github.com/rarora7777/curve-on-surface-vr-data.

For the MATLAB pre-processing code required for Phong projection, and the C++ code for building the Phong projection DLL: https://github.com/rarora7777/smooth-closest-point.

To use and build on the C#/Unity source code for the projection techniques described in the paper, read on.

To start, clone the repository including the submodules

git clone --recurse-submodules https://github.com/raora7777/curve-on-surface-drawing-vr

Then add this project to Unity and open it. The included example scene ./Assets/Scences/main.unity shows an example usage.

• Unity. Tested with Unity 2020.3 LTS, but it should work with Unity 2019.4 onwards, with some fiddling with SteamVR Unity Asset and Unity XR due to their ever changing APIs. https://unity3d.com/get-unity/download
• SteamVR. https://store.steampowered.com/app/250820/SteamVR/
• Steam required for SteamVR. https://store.steampowered.com/about/
• All other depdendencies are included.

• Add a StrokeMimicryManager component to any GameObject.
• Add The CameraRig prefab included with SteamVR.
• Add the model you want to use as a target surface for drawing curves and add a StrokeMimicryTarget component to it. This object does not need to have the MeshFilter component attached to itself, but one of its descendents must.
• Set the model name. You must include the target mesh as an OBJ file in the StreamingAssets folder ./Assets/StreamingAssets/<modelname>.obj. This folder can be modified: see the Inspector UI for StrokeMimicryManager.

• Download the pre-processing code below and follow the instructions to run it on your model.
• Add the generated files modelname_tri.txt, modelname_tet.txt, modelname_out.obj and (if generated) modelname_in.obj to the StreamingAssets folder or the custom path you set up above.
• If modelname_in.obj is generated, select the Load Inside Offset Surface checkbox in the Inspector UI for StrokeMimicryTarget.

• Only one StrokeMimicryTarget component should be active at a time. If multiple target objects (multiple objects with StrokeMimicryTarget components) are present and active before running the game, one will be arbitrarily selected. If multiple target objects become active only during gameplay, then the component activated last is selected.
• The brains of the code are in ./Assets/Scripts/Core/Projection.cs. Other files in Core are required helper classes. Files outside of Core are only required for the demo, and should probably be replaced in any real-world application.

Two controls are defined:

• Action. Hold the action button to draw or erase curves.
• Toggle. Press the toggle button to switch between drawing and erasing interactions.

Default Control Mappings

If this code is useful in a research project, please cite the following paper:

@article{arora2021midair,
	title={Mid-Air Drawing of Curves on {3D} Surfaces in Virtual Reality}, 
	author={Rahul Arora and Karan Singh},
	journal={ACM Trans. Graph.},
	volume={40},
	number={3},
	numpages={17},
	year={2021},
	month = jul,
	url = {http://doi.org/10.1145/3459090},
	doi = {10.1145/3459090},
	publisher = {Association for Computing Machinery},
	address = {New York, NY, USA}
}