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Light parameters #135

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0ef0ee3
typos
johguenther Nov 12, 2024
b6ebd7c
Clarify light brightness parameters
johguenther Nov 13, 2024
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4 changes: 2 additions & 2 deletions chapters/object_types/geometries.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -230,7 +230,7 @@ recognizes the following parameters:
| faceVarying.attribute1 |`ARRAY1D` of `FLOAT32` / `FLOAT32_VEC2` / `FLOAT32_VEC3` / `FLOAT32_VEC4` | | face-varying attribute1
| faceVarying.attribute2 |`ARRAY1D` of `FLOAT32` / `FLOAT32_VEC2` / `FLOAT32_VEC3` / `FLOAT32_VEC4` | | face-varying attribute2
| faceVarying.attribute3 |`ARRAY1D` of `FLOAT32` / `FLOAT32_VEC2` / `FLOAT32_VEC3` / `FLOAT32_VEC4` | | face-varying attribute3
| primitive.index |`ARRAY1D` of `UINT32_VEC4` / `UINT64_VEC4` | [(0, 1, 2, 4), (5, 6, 7, 8), {ldots}] | optional indices (into the vertex array(s)), each 4-tupel defines one quad
| primitive.index |`ARRAY1D` of `UINT32_VEC4` / `UINT64_VEC4` | [(0, 1, 2, 4), (5, 6, 7, 8), {ldots}] | optional indices (into the vertex array(s)), each 4-tuple defines one quad
|===================================================================================================

Parameter `vertex.position` must be set and contain at least four
Expand Down Expand Up @@ -347,7 +347,7 @@ recognizes the following parameters:
| faceVarying.attribute1 |`ARRAY1D` of `FLOAT32` / `FLOAT32_VEC2` / `FLOAT32_VEC3` / `FLOAT32_VEC4` | | face-varying attribute1
| faceVarying.attribute2 |`ARRAY1D` of `FLOAT32` / `FLOAT32_VEC2` / `FLOAT32_VEC3` / `FLOAT32_VEC4` | | face-varying attribute2
| faceVarying.attribute3 |`ARRAY1D` of `FLOAT32` / `FLOAT32_VEC2` / `FLOAT32_VEC3` / `FLOAT32_VEC4` | | face-varying attribute3
| primitive.index |`ARRAY1D` of `UINT32_VEC3` / `UINT64_VEC3` | [(0, 1, 2), (4, 5, 6), {ldots}] | optional indices (into the vertex array(s)), each 3-tupel defines one triangle
| primitive.index |`ARRAY1D` of `UINT32_VEC3` / `UINT64_VEC3` | [(0, 1, 2), (4, 5, 6), {ldots}] | optional indices (into the vertex array(s)), each 3-tuple defines one triangle
|===================================================================================================

Parameter `vertex.position` must be set and contain at least three
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64 changes: 41 additions & 23 deletions chapters/object_types/lights.txt
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Expand Up @@ -35,12 +35,11 @@ like `radius`.

Extension `KHR_LIGHT_DIRECTIONAL`

The directional light is thought to
be far away (outside of the scene), thus its light arrives (mostly) as
parallel rays. It is created by passing the subtype string `directional` to
<<object_types_light, `anariNewLight`>>. In addition to the <<object_types_light, general parameters>>
understood by all lights, the directional light supports the following
special parameters:
The directional light is thought to be far away (outside of the scene), thus its
light arrives (mostly) as parallel rays. It is created by passing the subtype
string `directional` to <<object_types_light, `anariNewLight`>>. In addition to
the <<object_types_light, general parameters>> understood by all lights, the
directional light supports the following special parameters:

.Additional <<api_concepts_parameters, parameters>> understood by the directional <<object_types_light, light>>.
[cols="<4,<3,>2,<12",options="header,unbreakable"]
Expand All @@ -51,16 +50,28 @@ special parameters:
| irradiance |`FLOAT32` | 1 | the amount of light arriving at a surface point,
assuming the light is oriented towards to the
surface, in W/m^2^
| radiance |`FLOAT32` | 1 | the amount of light emitted in a direction, in W/sr/m^2^;
`irradiance` takes precedence if also specified
| radiance |`FLOAT32` | | alternative specification of the brightness (if
`irradiance` is not explicitly set): the amount of
light emitted in a direction, in W/sr/m^2^;
|===================================================================================================

If `irradiance` and `radiance` are both explicitly set, then `irradiance` takes precedence.

[NOTE]
.Note
==================
Setting the angular diameter to a value greater than
zero will result in soft shadows when supported by the implementation. For
instance, the apparent size of the sun is about 0.53° or 0.00925 rad.
The main way to specify the brightness of the directional light via `irradiance`
and its alternative specification via `radiance` differ in their behavior when
the `angularDiameter` is changing: With `irradiance`, increasing the angular
diameter will result in softer shadows (when soft shadows are supported by the
implementation), but the overall brightness in the scene stays roughly the same.
With `radiance` however, increasing the angular diameter will also result in a
brighter illumination in the scene.
Using `radiance` is only meaninful if `angularDiameter` is larger than zero
(otherwise the directional light is not emitting any light).

Using a direction light with an angular diameter is a good approximation for
sunlight: the apparent size of the sun is about 0.53° or 0.00925 rad.
==================


Expand Down Expand Up @@ -98,24 +109,31 @@ Extension `KHR_LIGHT_POINT`

The point light (or with `radius > 0` the sphere light) is a light emitting
uniformly in all directions (from the surface toward the outside). It is created
by passing the subtype string `point` to <<object_types_light, `anariNewLight`>>. In addition to the
<<object_types_light, general parameters>> understood by all lights, the point light supports
the following special parameters:
by passing the subtype string `point` to <<object_types_light,
`anariNewLight`>>. In addition to the <<object_types_light, general parameters>>
understood by all lights, the point light supports the following special
parameters:

.Additional <<api_concepts_parameters, parameters>> understood by the point <<object_types_light, light>>.
[cols="<,<2,>,<6",options="header,unbreakable"]
|===================================================================================================
| Name | Type | Default | Description
| position |`FLOAT32_VEC3`| (0, 0, 0) | the position of the point light
| radius |`FLOAT32`| 0 | the size of the point light (becoming a sphere)
| intensity |`FLOAT32` | 1 | the overall amount of light emitted by the light in a
direction, in W/sr
| power |`FLOAT32` | 1 | the overall amount of light energy emitted, in W;
`intensity` takes precedence if also specified
| radiance |`FLOAT32`| 1 | the amount of light emitted by a point on the light source in a direction,
in W/sr/m^2^; `intensity` (or `power`) takes precedence if also specified
| Name | Type | Default | Description
| position |`FLOAT32_VEC3`| (0, 0, 0) | the position of the point light
| radius |`FLOAT32` | 0 | the size of the point light (becoming a sphere)
| intensity |`FLOAT32` | 1 | the overall amount of light emitted by the light in a
direction, in W/sr
| power |`FLOAT32` | | alternative specification of the brightness (if
`intensity` is not explicitly set): the overall amount of
light energy emitted, in W;
| radiance |`FLOAT32` | | alternative specification of the brightness (if neither
`intensity` nor `power` is explicitly set): the amount of
light emitted by a point on the light source in a
direction, in W/sr/m^2^
|===================================================================================================

The precedence order is `intensity`, `power`, `radiance`: the first (in this
ordering) explicitly set parameter is used.


[[object_types_light_quad]]
==== Quad
Expand Down