Types of Light in Metal API - swift

Question

I'd like to know if there are only Point Light and Ambient Light in Metal API or I can also use Spot Light and Directional Light in my 3D environment?
struct Light {
var color: (Float, Float, Float)
var ambientIntensity: Float
static func size() -> Int {
return sizeof(Float) * 4
}
func raw() -> [Float] {
let raw = [color.0, color.1, color.2, ambientIntensity]
return raw
}
}
How to implement Spot Light and Directional Light if they exist in Apple's Metal API?

Answer 1

The Metal API itself has no concept of anything as high-level as a “light”, in the same way that modern OpenGL doesn’t—the APIs for that kind of thing went the way of the dinosaur with the fixed-function pipeline. With modern low-level graphics APIs, you need to roll your own lighting; the excellent Metal By Example series has an article on doing that, though you may want to go through the earlier sections to get a clearer idea of what’s going on. Note that that article only deals with directional lights; spot lights are significantly trickier and you’ll need to do some research to find how those are usually done and then implement that approach in Metal.
As an alternative to using Metal directly, you might want to look into SceneKit, which is quite powerful and has built-in support for many types of light via the SCNLight class.

Answer 2

Marius gave me a hint that the MDLLight class is the abstract superclass for objects that describe light sources in a scene. When you load lights from an asset file using the MDLAsset class, or create lights when building an asset for export, you use one or more of the concrete subclasses MDLPhysicallyPlausibleLight, MDLAreaLight, MDLPhotometricLight, or MDLLightProbe.
...and MDLLightType is Enumeration that has options for the shape and style of illumination provided by a light, used by the lightType property:
case unknown = 0
0. The type of the light is unknown or has not been initialized.
case ambient = 1
1. The light source should illuminate a scene evenly regardless of position or direction.
case directional = 2
2. The light source illuminates a scene from a uniform direction regardless of position.
case spot = 3
3. The light source illuminates a scene from a specific position and direction.
case point = 4
4. The light source illuminates a scene in all directions from a specific position.
case linear = 5
5. The light source illuminates a scene in all directions from an area in the shape of a line.
case discArea = 6
6. The light source illuminates a scene in all directions from an area in the shape of a disc.
case rectangularArea = 7
7. The light source illuminates a scene in all directions from an area in the shape of a rectangle.
case superElliptical = 8
8. The light source illuminates a scene in all directions from an area in the shape of a rectangle.
case photometric = 9
9. The illumination from the light is determined by a photometric profile.
case probe = 10
10. The illumination from the light is determined by texture images representing a sample of a scene at a specific point.
case environment = 11
11. The illumination from the light is determined by texture images representing a sample of the surrounding environment for a scene.
These are excerpts from Apple Metal API Reference.
MDLPhysicallyPlausibleLight
A MDLPhysicallyPlausibleLight object describes a light source for use in a shading model based on real-world physics.
MDLAreaLight
A MDLAreaLight object represents a source of light that illuminates a 3D scene not from a single point or direction, but from an area with a specific shape. The shape of an area light is a two-dimensional figure in the xy-plane of the light’s local coordinate space, and its illumination is directed in the negative z-axis direction (spreading out from that direction according to the inherited innerConeAngle and outerConeAngle properties).
MDLPhotometricLight
A MDLPhotometricLight object represents a light source whose shape, direction, and intensity of illumination is determined by a photometric profile. You create a photometric light from a file in the IES format, containing physical measurements of a light source. Many manufacturers of real-world light fixtures publish such files describing the lighting characteristics of their products. This photometry data measures the light web surrounding a light source—measurements of the light’s intensity in all directions around the source.
MDLLightProbe
A MDLLightProbe object describes a light source in terms of the variations in color and intensity of its illumination in all directions. A light probe represents this variation either as a cube map texture, where each texel represents the color and intensity of light in a particular direction from the cube’s center, or as a set of spherical harmonic coefficients. In addition to describing such light sources, the MDLLightProbe provides methods for generating light probe textures based on the contents of a scene and for generating spherical harmonic coefficients from a texture.