Lights#

Several light and sky models are contained inside the Ignis rendering framework. Most number and color parameters can be connected to a shading network or texture via PExpr.

A light is specified in the lights block with a name and a type. The type has to be one of the lights listed at this section below.

{
    // ...
    "lights": [
        // ...
        {"name":"NAME", "type":"TYPE", /* DEPENDS ON TYPE */},
        // ...
    ]
    // ...
}

Note

The interface with PExpr is still experimental and will be further improved in the future.

Point Light (point)#

Parameter	Type	Default	Description
position	vector	`(0,0,0)`	Position of the point light.
intensity	color	`1`	Intensity of the point light given in radiometric [W/sr] or photometric [lm/sr] units. Can not be specified with power.
power	color	None	Power of the point light given in radiometric [W] or photometric [lm] units. Can not be specified with intensity.

Spot Light (spot)#

Parameter	Type	Default	Description
cutoff	number	`30`	Cutoff angle in degree. Greater angles will be completely black.
falloff	number	`20`	Falloff angle in degree. Greater angles will smoothly falloff towards the cutoff angle. Falloff angle should be less or equal to the cutoff angle.
position	vector	`(0,0,0)`	Position of the light.
direction	vector	`(0,0,1)`	Direction of the light towards the scene.
elevation azimuth	number	`0`, `0`	Instead of direction the elevation (in degrees above the horizon) and azimuth (in degrees west of south) of a celestial object can be used.
year month day hour minute seconds latitude longitude timezone	number	`2020`, `5`, `6`, `12`, `0`, `0`, `49.235422`, `-6.9965744`, `-2`	Instead of direction the time and location can be used. This will give the approximated direction from the sun. Latitude is given in degrees north. Longitude is given in degrees west. The timezone is given as an offset to the UTC.
intensity	color	`1`	Intensity of the light given in radiometric [W/sr] or photometric [lm/sr] units. Can not be specified with power.
power	color	None	Power of the point light given in radiometric [W] or photometric [lm] units. Can not be specified with intensity. The actual emitted intensity scales with the falloff and cutoff angle.

Directional Light (directional)#

Parameter	Type	Default	Description
direction	vector	`(0,0,1)`	Direction of the light towards the scene.
elevation azimuth	number	`0`, `0`	Instead of direction the elevation (in degrees above the horizon) and azimuth (in degrees west of south) of a celestial object can be used.
year month day hour minute seconds latitude longitude timezone	number	`2020`, `5`, `6`, `12`, `0`, `0`, `49.235422`, `-6.9965744`, `-2`	Instead of direction the time and location can be used. This will give the approximated direction from the sun. Latitude is given in degrees north. Longitude is given in degrees west. The timezone is given as an offset to the UTC.
irradiance	color	`1`	Output of the directional light in radiometric [W/m^2] or photometric [lm/m^2] units.

Area Light (area)#

Parameter	Type	Default	Description
entity	entity	None	A valid entity.
radiance	color	`1`	Output of the area light in radiometric [W/sr/m^2] or photometric [lm/sr/m^2] units. Can not be specified with power. This means if the entity is scaled up, the emitted energy increases!
power	color	None	Output of the area light in radiometric [W] or photometric [lm] units. Can not be specified with intensity. This means if the entity is scaled up, the emitted energy remains the same!

Sun Light (sun)#

Parameter	Type	Default	Description
direction	vector	`(0,0,1)`	Direction of the incoming sun towards the scene.
elevation azimuth	number	`0`, `0`	Instead of direction the elevation (in degrees above the horizon) and azimuth (in degrees west of south) of a celestial object can be used.
year month day hour minute seconds latitude longitude timezone	number	`2020`, `5`, `6`, `12`, `0`, `0`, `49.235422`, `-6.9965744`, `-2`	Instead of direction the time and location can be used. This will give the approximated direction from the sun. Latitude is given in degrees north. Longitude is given in degrees west. The timezone is given as an offset to the UTC.
irradiance	number	`1`	Output of the sun in radiometric [W/m^2] or photometric [lm/m^2] units.
radius	number	`1`	Radius of the sun seen from the earth. Can not be specified together with angle.
angle	number	`11.4`	Angular diameter of the sun seen from the earth. Can not be specified together with radius.

Sky Light (sky)#

Parameter	Type	Default	Description
ground	color	`1`	Ground color of the sky model.
turbidity	number	`3`	Turbidity factor of the sky model.
direction	vector	`(0,0,1)`	Direction of the incoming sun towards the scene.
elevation azimuth	number	`0`, `0`	Instead of direction the elevation (in degrees above the horizon) and azimuth (in degrees west of south) of a celestial object can be used.
year month day hour minute seconds latitude longitude timezone	number	`2020`, `5`, `6`, `12`, `0`, `0`, `49.235422`, `-6.9965744`, `-2`	Instead of direction the time and location can be used. This will give the approximated direction from the sun. Latitude is given in degrees north. Longitude is given in degrees west. The timezone is given as an offset to the UTC.
scale	color	`1`	Scale factor multiplied to the radiance.

This sky model is based on the paper “An Analytic Model for Full Spectral Sky-Dome Radiance” and the 2013 IEEE CG&A paper “Adding a Solar Radiance Function to the Hosek Skylight Model” both by Lukas Hosek and Alexander Wilkie, both Charles University in Prague, Czech Republic at that time.

CIE Uniform Sky Model (cie_uniform)#

Parameter	Type	Default	Description
zenith	color	`1`	Zenith color of the sky model.
ground	color	`1`	Ground color of the sky model.
ground_brightness	number	`0.2`

CIE Cloudy Sky Model (cie_cloudy)#

Parameter	Type	Default	Description
zenith	color	`1`	Zenith color of the sky model.
ground	color	`1`	Ground color of the sky model.
ground_brightness	number	`0.2`	Brightness of the ground.

CIE Clear Sky Model (cie_clear)#

Parameter	Type	Default	Description
zenith	color	`1`	Zenith tint of the sky model.
ground	color	`1`	Ground tint of the sky model.
ground_brightness	number	`0.2`	Brightness of the ground.
turbidity	number	`2.45`	Turbidity factor of sky model. This parameter can not be an expression (yet).
direction	vector	`(0,0,1)`	Direction of the incoming sun towards the scene.
elevation azimuth	number	`0`, `0`	Instead of direction the elevation (in degrees above the horizon) and azimuth (in degrees west of south) of a celestial object can be used.
year month day hour minute seconds latitude longitude timezone	number	`2020`, `5`, `6`, `12`, `0`, `0`, `49.235422`, `-6.9965744`, `-2`	Instead of direction the time and location can be used. This will give the approximated direction from the sun. Latitude is given in degrees north. Longitude is given in degrees west. The timezone is given as an offset to the UTC.
scale	color	`1`	Scale factor multiplied to the radiance.

CIE Intermediate Sky Model (cie_intermediate)#

Parameter	Type	Default	Description
zenith	color	`1`	Zenith tint of the sky model.
ground	color	`1`	Ground tint of the sky model.
ground_brightness	number	`0.2`	Brightness of the ground.
turbidity	number	`2.45`	Turbidity factor of sky model. This parameter can not be an expression (yet).
direction	vector	`(0,0,1)`	Direction of the incoming sun towards the scene.
elevation azimuth	number	`0`, `0`	Instead of direction the elevation (in degrees above the horizon) and azimuth (in degrees west of south) of a celestial object can be used.
year month day hour minute seconds latitude longitude timezone	number	`2020`, `5`, `6`, `12`, `0`, `0`, `49.235422`, `-6.9965744`, `-2`	Instead of direction the time and location can be used. This will give the approximated direction from the sun. Latitude is given in degrees north. Longitude is given in degrees west. The timezone is given as an offset to the UTC.
scale	color	`1`	Scale factor multiplied to the radiance.

Perez Sky Model (perez)#

Parameter	Type	Default	Description
direction	vector	`(0,0,1)`	Direction of the light towards the scene.
elevation azimuth	number	`0`, `0`	Instead of direction the elevation (in degrees above the horizon) and azimuth (in degrees west of south) of a celestial object can be used.
year month day hour minute seconds latitude longitude timezone	number	`2020`, `5`, `6`, `12`, `0`, `0`, `49.235422`, `-6.9965744`, `-2`	Instead of direction the time and location can be used. This will give the approximated direction from the sun. Latitude is given in degrees north. Longitude is given in degrees west. The timezone is given as an offset to the UTC.
luminance	color	`1`	Luminance of the sky model. Set this to 1 to prevent the parameter zenith to be applied.
zenith	color	`1`	Zenith color of the sky model. This can not be used together with luminance.
ground	color	`1`	Ground tint of the sky model. The ground has to be explicitly given.
a b c d e	number	`1`, `1`, `1`, `1`, `1`	Perez explicit parameters. Can not be used with other options specifying Perez parameters.
clearness brightness	number	`1`, `0.2`	Perez specified parameters to populate a, b, c, d and e. Will apply a diffuse normalization term. Can not be used with other options specifying Perez parameters.
diffuse_irradiance direct_irradiance	number	`1`, `1`	Diffuse horizontal irradiance (W/m^2) and direct normal irradiance (W/m^2). Will apply a diffuse normalization term. Can not be used with other options specifying Perez parameters.
diffuse_illuminance direct_illuminance	number	`1`, `1`	Diffuse horizontal illuminance (Lux) and direct normal illuminance (Lux). Will apply a diffuse normalization term. Can not be used with other options specifying Perez parameters.

Note

Output is in W m^-2 sr^-1 solar radiation, which equals the “-O 1” parameter in gendaylit from the Radiance framework. Support of the default “-O 0” is planned

Environment Light (env)#

Parameter	Type	Default	Description
radiance	color	`1`	Radiance of the sky model. This can also be a texture.
scale	color	`1`	Scale factor multiplied to the radiance. Only really useful in combination with a texture.
cdf	string	`"conditional"`	Internal method used for efficient sampling of the environment map. Can be one of “none”, “sat”, “conditional” or “hierachical”.