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Lighting

Light schemes for 3D graphics

Value Summary

InheritedAutomatic, Explicit, or None

Graphics Primitives

ObjectsLighting Default Values
plot::Scene3dAutomatic

Description

Lighting determines the light scheme used to illuminate a 3D scene.

With the default Lighting = Automatic, several light sources are set automatically to illuminate a 3D scene. Firstly, there is ambient white light of type plot::AmbientLight:

  • Light 0: LightIntensity = 0.25, LightColor = RGB::White

In addition, there are 6 directed lights of type plot::DistantLight with LightColor = RGB::White. Their directions is given as follows: Think of the graphical scene as being scaled to a standard box extending from - 1 to 1 in each coordinate direction. In these scaled coordinates, the directed lights shine into the directions given by the following Target attributes:

User-defined lights in the scene are ignored with Lighting = Automatic.

With Lighting = Explicit, the light sources set via Lighting = Automatic are switched off and user-defined light sources are switched on.

A plot command searches for light objects set by the user. If Lighting is not specified and any kind of user-defined light object is found in the scene, Lighting = Explicit is set automatically.

Switching between Lighting = Automatic and Lighting = Explicit in the inspector, one can easily compare the effect of the automatic lights with the effect of ones own lights.

With Lighting = None, the 3D shading algorithm based on reflections of light emitted from light sources in the graphical scene is switched off. This does not mean that the graphical scene turns black: all objects are painted in the color they are defined with. However, the scene will appear flat, because the depth of a 3D scene is created via the shading caused by different reflections of light at different points of the scene.

The maximal number of lights that can be used to illuminate a 3D scene depends on the OpenGL® driver installed on the computer.

    Note:   Some OpenGL drivers do not allow more than 6 light sources. If there are more light sources in the scene, the surplus lights are ignored. Lights that are switched off via Visible = FALSE are not counted.

After activating a 3D plot (by clicking it), the "Help" menu contains an item "OpenGL Info" that provides information about the maximal number of lights.

Examples

Example 1

In our first scene, no lights are specified. The default setting Lighting = Automatic is used:

f := plot::Function3d(sin(x^2 + y^2), x = -2..2, y = -2..2):
plot(f):

When specifying Lighting = Explicit, the lights set by the user are used. Since the scene does not contain any lights, the scene turns dark:

plot(f, Lighting = Explicit):

Lights are specified in the next scene. The setting Lighting = Explicit is used automatically:

Light0 := plot::AmbientLight(0.25):
Light1 := plot::DistantLight([ 1,  0, 1], [0, 0, 0], 0.3):
Light2 := plot::DistantLight([-1,  0, 1], [0, 0, 0], 0.3):
Light3 := plot::DistantLight([ 0,  1, 1], [0, 0, 0], 0.3):
Light4 := plot::DistantLight([ 0, -1, 1], [0, 0, 0], 0.3):
plot(f, Light0, Light1, Light2, Light3, Light4):

We switch off the parameter lines:

plot(f, Light0, Light1, Light2, Light3, Light4,
     XLinesVisible = FALSE, YLinesVisible = FALSE,
     Axes = None):

In the next scene, the 3D shading model is switched off via Lighting = None:

plot(f, Lighting = None):

In the previous picture, the axes box and the mesh lines are switched on and create a certain 3D effect. After switching the box and the mesh lines off, the scene appears flat when rendered without shading:

plot(f, Lighting = None, Axes = None,
     XLinesVisible = FALSE, YLinesVisible = FALSE):

delete f, Light0, Light1, Light2, Light3, Light4:
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