Geometries
Geometries
Embedded Files
Geometries for Predict Engine are defined just like geometries for the Unreal Engine level. Predict Unreal supports every geometry format that is supported by Unreal Engine.
Normals
Normals
The normals of a geometry are the directions perpendicular to the surface at each position on the geometry. In Predict Engine, normals indicate the exterior side of the geometry. When setting a material on a geometry, the material is placed on the internal side of the geometry.
Figure A : Visualisation of the normal vectors of a surface
https://en.wikipedia.org/wiki/Normal_(geometry)
By default, opaque materials are NOT considered to be "double sided" in Predict Engine. That means the internal side of opaque materials are displayed in black (see example 1b).
NB : in the alpha plugin, this option cannot be edited.
When the double sided option is enabled, the normal direction is ignored and the material is applied on both sides of the geometry (see example 1a).
NB : the double sided option only affects opaque materials, it does not affect transmissive materials.
example 1a : both cubes are made of a blue coloured diffuse material (Lambert).
The cube on the left has normals facing outwards (correct). The cube on the right has normals facing inwards (incorrect).
Double-sided option is enabled.
example 1b : same scene as example 1a.
Double-sided option is disabled.
Specular materials can be transmissive : the light is not only reflected by the material but it can be transmitted and go through the material. In these situations, the normals of the geometry are very important, they define which material should be set on each side of the geometry : the external material (air by default) is used on the side pointed by the normals, the internal material is used on the other side.
When the normals of a geometry are not defined correctly (the normals are pointing inside the physical geometry), the external material is used inside the physical geometry. This can lead to incorrect rendering (see example 2).
example 2 : both spheres are made of a blue coloured glass (Fresnel transmissive material).
The sphere on the left has normals facing outwards (correct). The sphere on the right has normals facing inwards (incorrect).
Unreal Engine import options for geometries may have a great impact on the way geometries are represented. For instance, we noted the impact of the "High Precision Tangent Basis" option on the aliasing of the reflections. If you have trouble with normals, don't hesitate to try other import options and contact us so we can try to take this settings into account in following plugins.
example 1 : visualization of a geometry with a mirror material, imported with the "Use High Precision Tangent Basis" disabled. The reflections are aliased.
example 2 : same scene with the "Use High Precision Tangent Basis" enabled. The reflections are not aliased.
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