Engine Details

This application is based in Unreal Engine 4, version 4.25. The application was developed on Windows 10. Non-default Unreal plugins used are Color Wheel version 2020.1.4, Easy File Dialog version 2.0, RuntimeMeshImportExport version 1.11, and RuntimeTransformer version 1.0. The application uses Unreal Engine 4's Raytracing features to produce high quality images.

Model Loading Backend

Model loading is done through use of the RuntimeMeshImportExport Unreal Engine Plugin, which enables models to be loaded at runtime from the user's PC. The plugin allows for files of a variety of formats, and theoretically has texture support, though the files we tested on didn't appear to work. See Fig 2. for a the Blueprint Implementation. We ended up using a workaround for texture loading, detailed below. Point cloud loading is also supported, but isn't a focus of the application.

Texture Loading

Because of the difficulty with getting correctly formatted files to be loaded by the RuntimeMeshImportExport Plugin, we instead opted for a practical solution of expecting the textures to be located in the same folder as the model file with a particular suffix. Specifically, the model viewer can load in a diffuse, specular, and normal texture along with the model. The suffixes are "-DIFFUSE", "-SPECULAR" and "-NORMAL" respectively. An example of a proper folder setup can be seen in Fig 3.

File Dialog

File dialogs are used to make locating the files to be loaded much simpler. This is accomplished in a very straightforward manner using the File Dialog plugin, which allows for string filepaths to easy be obtained for use by the RuntimeMeshImportExport plugin.

Camera Control

The camera control utilizes Unreal's built in camera options. A spring arm component is used to achieve the standard camera behavior, of rotation around a center point. Additionally, free camera and perspective toggles were added to make the camera usage experience more intuitive. The free camera simple uncouples the camera from the spring arm component, and perspective toggle is done trivially by editing the camera settings. A cinecamera was used over a standard camera, as it provides extra options in terms of aspect ratio, depth of field, and other cinematic effects.

Lights

The three types of lights in use by the Model Viewer are point, directional, and HDRI. HDRI is the most generally useful, as it provides a good looking background and realistic looking ambient light. It uses a cubemap to define the environment, and is implemented through Unreal's built in HDRIbackdrop. The point and directional lights are handled through spawning a point or directional light actor into the environment, but of course they are not useful without a method of moving them, as detailed below.

Movement Gizmo

To allow for the scene to be manipulated, we used the RuntimeTransformer plugin, which provides editor-style movement gizmos to be used to manipulate objects in the scene, in our case lights and loaded models. The blueprint allows for objects to be selected via clicking and dragged.

Color Wheel

We use the Color Wheel plugin to allow the color of the lights to be changed dynamically. The plugin is simple to use, and the color wheel menu, only shows when a relevant object (i.e. light) is selected.

User Interface

The User Interface is a simple but effective use of Unreal's UI Widget system. Fig 4. shows the setup used for the widget. The buttons trigger events that are executed in the level blueprint, allow the user easy and intuitive access to the core functionality of the Model Viewer.

Gizmo Interface

The Gizmo interface is separate from the main user interface, and interacts only with the Gizmo controls. These are based heavily on the example blueprints provided by the RuntimeTransformer plugin. The Gizmo interface can be seen at section C of Fig. 1. It provides rotation, translation, scale, and snapping settings.

Rendering

Output rendering is done through Unreal's HighResShot console command, which allows for renders to be create at any resolution. The Model Viewer provides the user the option to select an output location through the Easy File Dialog plugin, and to select a multiplier for the output resolution. Though the process for obtaining a screenshot is theoretically simple, a lot of code is required to make sure the output image is presentable. Particularly, all lights placeholder meshes, gizmos, and UI needs to be absent in the final image. To this end, all light meshes are made invisible during the render, and reenabled after, and the currently selected object is deselected. This process can be seen in Fig 5. There are several alternative methods that we explored before arriving at HighResShot, that could work for other similar projects. The Movie Render Queue is a very high quality option, but is only available at runtime in Unreal 4.26+. Another option explored was NVIDIA Ansel, which is a very powerful tool but is unfortunately incompatible with Unreal Raytracing and AMD hardware.