The Complete glTF to PRC/U3D Conversion Guide

Texture Compression Support:

glTF: Full support | PRC/U3D: Partial support

PRC/U3D Notes:

Basic texture compression for document embedding

Impact:

Texture compression refers to a process of compressing 2D texture images for memory-efficient rendering (and sometimes for efficient transmission). The decompression of compressed texture data is therefore performed on-the-fly during rendering, so that it never has to be stored in unpacked form, but can be kept as-is in GPU memory. Formats supporting texture compression methods, such as the ones offered by glTF through KTX2 containers, therefore allow 3D models to use a smaller memory footprint on the client device during rendering. This can speed up rendering time, and also make it possible to store and use larger amounts of texture data than it would otherwise be possible.

Normal Mapping Support:

glTF: Full support | PRC/U3D: Partial support

PRC/U3D Notes:

Limited normal mapping support

Impact:

Normal maps are used to model shading differences that are arising from small geometric details on a surface, such as fabric structures, visible gaps between bricks forming a wall, or rough rock surfaces. In this example, a normal map is used to model a fabric structure. Without support for this feature, the rendered fabric will look smoother than it actually is in the real world, as the fabric structure won't be visible.

PBR Materials Support:

glTF: Full support | PRC/U3D: No support

Impact:

PBR materials enable Physically-Based-Rendering (PBR) for a standardized, photorealistic look of rendered images. PBR uses concepts like metallic-roughness or specular-glossiness properties and a microfacet-based modeling of the surface, using a concept called BRDF (Bi-Directional Reflectance Distribution Function). In this example, PBR materials are used to achieve realistic looking plastic and metal materials. Without support for PBR materials, only basic colors and shading can be used (for example, based on more simple shading models, such as the Blinn/Phong model).

Skinned Animations Support:

glTF: Full support | PRC/U3D: Partial support

PRC/U3D Notes:

Basic skeletal animation support in U3D

Impact:

Skinned animations are commonly used for 3D character models in interactive applications, such as games or virtual worlds. They make it possible to easily animate the 3D model using a helper structure based on virtual bones, composing a virtual skeleton for animation control. In this example, a skinned animation is used to pose a 3D character. Without support for skinned animations, the 3D model will remain in its default pose, such as the default T-pose.

Morph Targets Support:

glTF: Full support | PRC/U3D: Partial support

PRC/U3D Notes:

Simple morphing capabilities

Impact:

Morph Targets, or "Blend Shapes", are commonly used to animate facial expressions and soft surfaces, for example cloth under a cloth simulation. They model various states of the animations with different vertex positions. In contrast to skinned animations, morph targets do not use any virtual bones, but work solely on the vertex data. In this example, a facial animation is achieved through morph targets. Without suport for this feature, in this example, the face will not show the animation.