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Lights

This chapter describes the different types of lights which you can create using N-Geometry and the Lights Editor itself. It also describes the parameters you can use to control the appearance and behavior of lights in your scene.

Creating Lights

N-Geometry provides you with several types of lights for illuminating shaded or rendered objects:

ambient

point

infinite

spot

These lights, and their characteristics are described in more detail below.

Initially, the view window contains a single default point light positioned at 100, 300, 150 (up and back) so that it illuminates all visible objects.

You can create lights from the Attributes Editor and from N-Geometry.

From N-Geometry:

1. (CLICK-L) on New Object>Light.

From the Attributes Editor:

1. (CLICK-L) on Lights in the Attributes Editor mode line.

2. (CLICK-L) on New in the LIghts File Operations section of the Lights Editor menu.

The new light parameters menu appears. Use this menu to specify the type and characteristics of your new light. This menu is described in detail in "Defining Light Parameters," on page 4-10.

Light Types

N-Geometry creates the following types of lights:

Ambient

Ambient lights do not have a location; rather, they simulate the infinite number of reflections of the ambient light in a typical room.

Point

A point light is a "dimensionless" point in space that emits a light in all directions.

Note. If you place a point light inside a partially transparent object, you can make that object appear to glow.

Infinite

An infinite light is similar to a star; it is essentially an infinite distance from any object in a scene, so all its rays strike an object at the perpendicular. These lights are useful for lighting only one side of objects in a scene (for example, a planet lit by a distant sun).

Spot

A spot light emits light in a cone or pyramid shaped projection (depending on the shape of the spot pattern), from the tip of the light to the pattern described by the base of the light. You can adjust two projection at the base of the light; the inner shape shows the umbra (where light has 100% of its specified intensity), while the outer shape shows the penumbra (where the light gently falls off to zero for a soft edge). Spot parameters are discussed in detail in the section "Spot Attributes," on page 4-18.

Selecting Light Sources

When manipulating light sources in N-Geometry, you must specify the type of object to be manipulated.

For spot and point lights, select points in the element sensitivity menu.

For infinite lights, select segments in the element sensitivity menu.

All lights can be selected through the Browser.

Assigning Lights and Light Groups

When you set up a scene for rendering, you must provide for lighting the scene. You do so by assigning a light group, or groups, to materials, which are in turn assigned to objects in the scene. Although you can create a light in Geometry, it will have no effect upon the rendered scene until it is placed in a light group and associated with a material.

Default Lights

If N-Render encounters an material in the scene that has not been assigned a light, it uses a default light group (consisting of the default point light) to illuminate that object.

Note. This default light is not the default point light that is created when N-Geometry starts up. N-Render has a default point light "built-in" which is located on the Z-axis.

If you really want an object to render black, assign a light to the light group assigned to the material assigned to that object and set its brightness to zero.

Editing Lights

To create new lights and light groups, or edit existing lights for each domain, (CLICK-L) on the Lights button on the Attributes Editor modes bar:

Figure 4.1 The Light Editor

Defining Light Attributes

The appearance and effect of a light on a rendered scene is dependent upon the current domain and the type of light. Most parameters are similar for Point, Infinite, and Ambient lights for the four domains. However, spot lights are somewhat more complex, and offer a richer set of attributes. For this reason, they'll be discussed separately.

Parameters for the current light are displayed in the Light Parameters section of the Light Editor menu:

Figure 4.8 Light Parameters menu for a spot-light

Attributes for each parameter appear in the Light Parameters section of the Lights Editor menu.

Shader Attributes

Shader attributes control the way in which the light is interpreted by the shader for the current domain.

Color

Specifies the color for the light. (CLICK-L) on the color field.

Brightness

Controls the intensity of the light. A lower number means a dimmer light.

Attenuation

Point and Spot lights

Attenuation is the manner in which the brightness of a light drops as a function of distance from the light object. In the real world, the intensity of a light diminishes in proportion to the square of distance. In N·World, you can rewrite the laws of physics to suit your own, specialized requirements.

The distance a light travels is considered to be finite (the distance between the light and the aimpoint for a spot light, or the radius for a point light). Attenuation is expressed in terms of a percentage of this distance rather than in absolute terms.

Figure 4.9 Attenuation

You can configure the brightness of a point or spot light to decline with distance away from the light.

% of no Falloff - The percent of the light distance for which there is no change in light intensity (labeled "A" in Figure 4.9).

% of Linear - The percent of the light distance during which light intensity declines linearly (labeled "B" in Figure 4.9, the curve at this point has a slope of 1).

% of Square - The percent of the light distance during which light intensity declines by the square of distance (labeled "C" in Figure 4.9, the function which describes the curve at this point is quadratic).

Radius is the radius of the light (the base of the cone in a spot light, or the actual radius of the light's effect for a point light)

You can use any combination of attenuation attributes for a given light.

Raytrace?

Render domain only

Toggles raytracing for the current light.

Shadow Color - The color for any shadows generated by the light.

Ray Displacement - The distance between the point at which a ray strikes a surface and the reflected ray leaves the surface. This is necessary to prevent situations where rays bounce back and forth along or loop around the same paths endlessly.

Figure 4.10 Ray displacement. Left, no displacement; right, displacement

Spot Light Parameters

Spot lights have several unique parameters, depending upon the current render domain. You can also control the position of the light and its orientation in N-Geometry. For more information on manipulating lights in N-Geometry, see the N-Geometry Reference Guide.

Spot Attributes

(CLICK-L) on the Spot icon to specify attributes specific to the spot light.

Spot Pattern

These options control the shape of the spot pattern. The spotlight icon changes in appearance to reflect the current spot pattern selection:

Circle - the base of the spotlight is circular.

Rectangle - the base of the spotlight is rectangular.

None - the base has no pattern.

Figure 4.11 Spot pattern icons. Left, circular spot; center, rectangular spot; right, no spot

Spot Angle

Adjusts the spot angle for the selected spotlight:

Figure 4.12 Left, original light; right, same light with enlarged spot angle

Falloff Angle

Changes the area where light falloff begins around the edges of this light's spot pattern. This operation is interactive:

Figure 4.13 Left, original light; right, same light with modified falloff angle

Light within the inner portion of the spot pattern strikes an object at full intensity; falloff begins between the solid and dotted line in the spot pattern.

Aspect Ratio

Interactively updates the aspect ratio of the selected spotlight's spot pattern. This works for both circular and rectangular spot patterns.

Figure 4.14 Left, original light; right, same light with modified aspect ratio

Radius

The radius of the light object (the sphere shaped object emitting the light).

Note. This is not the radius of the spot pattern!

Shadow Map Attributes

Render domain only

Shadow maps give you a high level of control over the quality and appearance of the shadows you use to light a scene.

Shadowing

Specifies whether or not the spot light should cast a shadow.

Off - the light does not cast a shadow.

On - the light does cast a shadow.

Shadow Only - the light casts a shadow, but no light.

Figure 4.15 Left, spot light with shadowing off; right, spot light with shadowing on

Opacity

The opacity of the shadow. A higher value makes the shadow appear more solid. Shadows have a maximum opacity of 1.0 (solid black).

Static Map

Static shadow maps can be used to significantly reduce render times in which the shadow information does not change. You can specify a static shadow map for lights whose position and relationship to other objects in the scene does not change.

Yes calculates the shadow map only for the first frame; the same shadow map is used for all subsequent frames. If you don't specify a particular static map, a default name for the static map image file is inserted into the Map Name field.

No forces a shadow map to be drawn (if required) at each frame.

Default Limits

The default limits specify the minimum and maximum size of the shadow map to be used when generating a shadow. Specifying larger maximum values produce more detailed shadows, but take longer to render.

Finding a good range is a function of how much detail you need in a shadow, and may require several test renders. For example, if most of your shadows are being cast on objects that are a good distance from the camera, you could specify lower Min and Max values to speed up the render. If you need lots of detail, or the camera is close to the shadows, you may need a higher minimum value.

Figure 4.16 Left, shadow using shadow map size of min=32 and max=32; right, using defaults of 256 and 2650

Sampling Limits and Jitter Limits

These parameters control the overall quality of the shadow. Increasing the range for any of these values increases the quality of the shadow, but also increases the amount of time required to render the scene.

Projection

You can specify an image through which the light is projected, much like a slide in a slide projector.

Map

(CLICK-L) on this field to specify the image through which to project the light.

Figure 4.17 Left, normal spot light; right, with projection map

Shader

Determines the shader used to render the project map.

Point - Quickest, lowest quality.

Jitter - Medium speed, medium quality.

Summed - Slowest, highest quality.

For a more detailed description of shader options and performance characteristics, see "Shader," on page 2-10.

Map Opacity

The opacity of the projected image.

Darkness

A factor applied to the brightness of the applied map. The default is 1, which has no effect. A value less than one decreases brightness of the projected map; a value larger than one increases brightness.

The Light Group Editor

One of the parameters you define for a material is the Light Group. A light group consists of one or more N-Geometry lights. By assigning different light groups to different materials used to render a scene, you can make certain objects stand out more, or create other unique lighting effects.

Suppose, for example, that you have a cube at the center of your scene that you want to be particularly bright. You could define two light groups-one for the cube and one for all the other objects in the scene. When you created the material for the cube, you'd specify the special light group, while for other materials used to render the rest of the scene, you could use the default light group.

When you first add a light to N-Geometry, it is automatically assigned to the default light group. If you want all the objects in your scene to be equally affected by the lights you specify, you need not build any light groups; simply use the default light group for any of the materials you use to render the scene.

Note. A light can belong to more than one light group.

(CLICK-L) on Light Groups in the light editor mode line to manipulate light groups. The Light Group Editor appears:

Figure 4.18 Light group editor

The lights currently loaded into N-Geometry are displayed in a list from top to bottom on the left side of the menu. The light groups are displayed across the top of the menu. To add or remove a light to or from a selected group, simply toggle the appropriate box.

Note. A default point light exists in the event that you try to render with no lights specified. As soon as you create any light, the default light is turned off.

Assigning Lights to Objects in a Scene

Lights, like materials, cannot be assigned directly to an object. Rather, you must create a material which is applied to an object; materials can specify a light group.

There are four basic steps to making a light affect some objects in the scene but not others:

1. Create the light.

2. Assign the light to a light group.

3. Assign the light group to a material.

4. Assign the material to your object.

Objects rendered with a material that specifies a particular light group are rendered using only the lights in that group; thus, it is possible to get objects in very close proximity with significantly different lighting characteristics.

Light Group Commands

The following commands let you create, load, save, delete, and rename light groups.

New

(CLICK-L) here to create a new light group. You are prompted to enter a directory and filename for the new group.

Load

Load a previously saved light group.

Save

Save one or more of the currently loaded light groups.

Delete

Removes one or more of the currently loaded light groups from memory.

Note. To remove a light group from disk, you must do so from a UNIX shell.

Rename

Renames one or more of the currently loaded light groups in memory. You must re-save the light group for the new name to be saved to disk.

Mini-Tutorial 3: Creating a Light Group

It's easy to create a light group.

1. Use the procedure detailed on page 4-2 to create several lights.

2. (CLICK-L) on Light Groups to enter the Light Group Editor.

3. (CLICK-L) on New Group.

Enter a directory and filename for the light group in the dialog box that appears.

4. Enter a name for your new group, and (CLICK-L) on Do It.

You new group appears as a column in the light group editor display.

Figure 4.19 New group in the light group editor display

All the currently loaded lights are displayed along the left side of the light group editor. To add a light to a light group, (CLICK-L) on the gray square.

5. (CLICK-L) on Save.

6. (CLICK-L) on your new light groups, then (CLICK-L) on Do It.

Your new light group is saved to file. Light group files have the file extension .lg.

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