init(_:)
Creates an object containing surface details for an entity from a custom material’s normal property.
Declaration
init(_ value: PhysicallyBasedMaterial.Normal)Parameters
- value:
The normal object from a Physicallybasedmaterial.
Discussion
This initializer creates an object by copying the normal map from the normal property of a PhysicallyBasedMaterial.
Normal mapping is a real-time rendering technique that captures fine surface details for a model by using a texture instead of by increasing the number of polygons in the model. It works by storing surface normals, which are vectors perpendicular to the surface of the model, from a much higher-resolution version of the same 3D object. A normal map stores each vector in the image by storing the vectors’ X, Y, and Z values as the R, G, and B components of the corresponding pixel in the UV-mapped image.
To render an entity using a normal map, set lightingModel to CustomMaterial.LightingModel.lit or CustomMaterial.LightingModel.clearcoat, and call params.surface().set_normal() from its surface shader.
The following Metal code demonstrates how to sample and use a value from the normal map in your surface shader function:
// Retrieve the entity's UV texture coordinates.
float2 uv = params.geometry().uv0();
// Models loaded from USDZ or Reality Composer use UVs that are flipped
// on the y-axis. This compensates for that.
uv.y = 1.0 - uv.y;
// Sample the normal map texture based on the resulting UV coordinates.
auto tex = params.textures();
float3 normal = (float3)tex.normal().sample(textureSampler, uv).rgb;
// Set the sampled value as this pixel's normal.
params.surface().set_normal(normal);