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Figure 23-6: Rendering compared with Conceptual visual style.

Before rendering a 3D model, you need to do the following:

Add lighting to highlight features and define shadows.

Apply materials to 3D objects by face, object, or layer.

Set up a background for your 3D model to be rendered against.

All the above-mentioned items help to bring realism to a 3D model. This chapter focuses on each of these tasks before covering the steps to create a rendering.

Adding Lighting

One of the key ingredients in the soup that makes a rendering look good is lighting. Lighting helps give a model depth through the use of highlights and shadows. Just as in the real world, objects that are closest to the light source appear the brightest and those the farthest away appear the darkest.

The two types of lighting in AutoCAD are default and user-defined. Default lighting, as its name suggests, is on and available in every drawing, and it’s what gives some basic form to your 3D model when you click the Render button before you add lighting of your own. All types of user-defined lights can cast shadows. Most tools that you use to create and edit lights are located on the Lights and Sun & Location panels of the Render tab.

Default lighting

Over the past few years, AutoCAD’s default lighting has improved in quality. Prior to AutoCAD 2007, default lighting consisted of a single, distant light source, always directed toward the target of your current view from behind your back. AutoCAD 2007 added a second default light to help increase the lighting level, and to balance the lighting in a viewport.

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526 Part V: On a 3D Spree

Default lighting can’t cast shadows, so we don’t recommend using it for final renderings. It does work pretty well for quick conceptual renderings, however. You can control the brightness, contrast, and midtones levels for default lighting with the slider controls on the slideout of the Lights panel on the Render tab of Ribbon (see Figure 23-7).

Figure 23-7: AutoCAD to lights, extra brightness is a go.

Use the DEFAULTLIGHTING system variable to enable and disable the use of default lighting in the current viewport. Set DEFAULTLIGHTING to 0 when you want user-defined lighting to render your 3D model. If you’re using default lighting, the DEFAULTLIGHTINGTYPE system variable controls whether one or two default distant lights are used. When set to 0, one default light is used; when set to 1, two default lights are used.

User-defined lights

Default lights are fine for quick renderings, but they don’t bring your renderings to life in the way that user-defined lights can. User-defined lights are lights that you create — with one exception — and modify in your 3D model. The only user-definable light type that you can enable and modify, but can’t create, is the sunlight system.

The first time that a user-defined light is placed in a drawing, the Lighting – Viewport Lighting Mode alert box is displayed, advising you that you need to turn off default lighting in order to see light from user-defined sources.

Click Turn Off the Default Lighting to disable default lighting. (To turn default lighting back on, open the Lights panel slideout on the Render tab and click

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Default Lighting.) You should always disable default lighting when using userdefined lights; otherwise you can end up overlighting your model, making it look unnatural.

The two types of user-defined lights that you can create are generic and photometric:

Generic lights: Provide advanced control over how they emit light and are much more complex than photometric lights.

Photometric lights: More convenient to use as they are defined to represent how lights work in the physical world.

The LIGHTINGUNITS system variable controls whether user-defined lights in your drawing are represented as generic or photometric lights. When LIGHTINGUNITS is set to 0, generic lights are used. When LIGHTINGUNITS is

set to 1 or 2, photometric lights are used; 1 indicates American lighting units, and 2 indicates International lighting units. Lights don’t have to be removed and added to switch between generic and photometric lights; you just need to switch the system variable.

To add a user-defined light to your drawing, click the lower half of the Create Light split button on the Lights panel of the Render tab. You can choose from four distinct types of lights on the flyout (for the differences between the light types, see Figure 23-8):

Point light: Emits light uniformly in all directions, but the emitted light falls off the farther it gets from the source. A point light is similar to a candle or a lantern.

Spotlight: Emits light in a specific direction. As light travels farther from the source, it spreads out in the shape of a cone. You can define the hotspot — the brightest part of the emitted light — and the fall-off of the light.

Distant light: Emits light along a specified vector and doesn’t decay or fall off like other user-defined lights do. A distant light is similar to the sun.

Weblight: A cross between a point light and a spotlight. Weblights are available only when using photometric lights, and the way they emit light is determined by an IES file. IES files are provided by lighting companies for use in products like AutoCAD to mimic the lights that they manufacture.

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528 Part V: On a 3D Spree

Distant light Weblight

Figure 23-8: Lighting primitives with the four types of user-defined lights.

AutoCAD and we both strongly advise against using distant lights when using photometric lighting. If you decide to ignore this warning, make sure to turn down the intensity factor of the distant light to avoid washing out your rendering.

Point lights, spotlights, and weblights can be selected and edited directly in a drawing because a glyph is displayed to show where the light is located. Distant lights do not have an associated glyph. (A glyph is a nonprinting object displayed in a drawing that enables you to select an object that is not part of the actual model.)

Shadows . . . or no shadows?

AutoCAD allows you to define lights that can’t generate shadows. This might seem illogical because shadows are cast when light is obscured by an object. This is important because you may want to fill an area with light but not have it affect the way shadows are cast.

To control the shadows a light can generate, select a light, right-click, and then choose Properties to open the Properties palette. The Shadows option in the General category enables or disables shadow creation from

the selected light. The Rendered Shadow Details category gives you a large degree of creative control over shadow appearance. For more information on putting your objects in the shade, open the online help and search on Render

3D Objects for Realism.

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