Render Domains

A material can be used in one or more domains; each render domain has a different set of attributes that can be specified to take advantage of that domain. This chapter describes the attributes for the GL Shade and the Render domains. (Attributes for the various game domains is described in more detail in the appropriate Game Express manuals.)

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GL Shade Domain

Setting GL Shade Preferences

Figure 3.1 The GL Shade domain defaults menu

Map Directory

• (CLICK-L) on the Map Directory field to place the cursor in the field and edit it.
• (CLICK-M) on the Map Directory field to clear the directory and specify a new one.
• (CLICK-R) on the Map Directory field to specify a new directory or project interactively using a Choose Directory pop-up, as described in Getting Started.

After specifying a map directory, (CLICK-L) on one of the buttons at the bottom of the dialog box:

• (CLICK-L) on Done to use the specified directory for the current N·World session.
• (CLICK-L) on Save Preferences to save the specified directory to file (as your default).
• (CLICK-L) on Abort if you change your mind.

Shader Attributes (GL Shade)

Figure 3.2 GL Shade shader attributes

Diffuse Color

Shininess

Specular Color

Emission Color

Smooth Shade?

Outline Faces

Texture Parameters (GL Shade)

Texture Map

Figure 3.3 Select map file (shown here with icons on)

• Options - (CLICK-L) on Options, then (CLICK-L) on the Icons toggle to show the thumbnail-sized icon for each image file, if it exists. Icon files are created automatically by N-Paint when an image is loaded into memory.

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Render Domain (N-Render)

Setting Render Domain Preferences

Figure 3.4 Setting N-Render defaults

Output Directory

Output Name

Map Directory

Output Window

• Render Window outputs to the Render Display Window.
• Paint Canvas automatically loads the rendered image into N-Paint.

Render Width

Render Height

Render Gamma

Output Format

Figure 3.5 Select output format pop-up menu

Background

• Clear erases the window before rendering to it.
• Existing Image renders the scene over the existing image.

Anti-Alias

Ray Depth

Ray Power

Ray traced images have a more natural look and feel to them; the ability of a ray tracing renderer to simulate the bouncing of light found in real-world environments makes it simple to create lifelike images like the one shown in

Figure 3.6 Sample ray traced image

Pixel Filter

Compute Matte?

Dither Image?

Enable Shadows?

Show Render Time?

Display Render?

• At End shows the completed frame after it has been rendered.
• During shows each line of the render as it is completed, so you can tell how far the render has gone.
• None does not display the rendered frame (even though it is generated).

Save Render?

Fog Color

Shadow Smoothness

Shadow Map Min and Shadow Map Max

Saving Preferences

• (CLICK-L) on Done to save changes to Render preferences for the current session.
• (CLICK-L) on Save Preferences to save Render preferences to file (these will be the defaults each time you start N-Render.
• (CLICK-L) on Abort to discard changes you've made.

Shader Attributes (N-Render)

• Flat renders without calculating diffusion or specular components. This is a fast shading model, suitable for background images which require no shading. Objects and backgrounds rendered with materials using this shading model have a flat, non-glossy appearance.
• Lambert calculates the diffusion component, but not the specular component for a rendered image. Objects rendered with materials using the Lambert shading model appear "flat."
• Phong is suitable for objects made of plastic. It calculates both a diffusion and a specular component for objects lit in a scene. Objects rendered with materials using the Phong shading model are characterized by a specular highlight.
• Blinn is suitable for objects made of metal. This shading model is Blinn's implementation of the physical shading model for surface reflection developed by the applied physicists Torrance and Sparrow.
• Cook is also suitable for metal objects. The Cook shading model is similar to the Blinn model, except it takes into account the angle of the viewer in relationship to the scene when rendering any specular highlights.

A change in the viewer's angle causes a specular shift, which is faithfully rendered using this model. This specular shift takes into account the polarizing effect of metal surfaces on reflected light.

Each model uses a subset of the render attributes described below to achieve its "look." The shader attributes that can be specified with each shading model are described in Table 3.1:

Table 3.1 Shading Model Parameters (by shading model)

Attribute	Flat	Lambert	Phong	Blinn	Cook
Raytrace?	·	·	·	·	·
Reflectance	·	·	·	·	·
Refractance	·	·	·	·	·
Index	·	·	·	·	·
Color	·	·	·	·	·
Color Opacity	·	·	·	·	·
Specular Color			·	·	·
Specular Exponent			·	·	·
Ambient Gel		·	·	·	·
Directional Gel		·	·	·	·
Fresnel					·
Visibility	·	·	·	·	·
Highlight Opacity			·	·	·
Smooth Shade?	·	·	·	·	·
Facing Control	·	·	·	·	·
Light Group	·	·	·	·	·

Ray Trace

• Reflectance - Surface reflectance. A higher value makes the surface of the object rendered with this material more reflective (rays don't lose as much strength when striking the surface).
• Refractance - Surface refractance. A higher value means more interior detail will be rendered.
• Index - The refractive index for any object rendered with this material. A higher value means an object bends (refracts) light to a greater degree.

Color

Color Opacity

A value of 1.0 creates a completely opaque object, while a value of 0.0 produces a completely transparent object.

Note. When using shading models that support specular highlights, make sure that the highlight opacity and object opacity match. Otherwise, the object can appear more transparent, while the specular remains more visible.

Specular Color

Specular Exponent

• With the Phong shading model, a lower value produces a more prominent specular highlight.
• With the Blinn and Cook shading models, a higher value produces a more prominent specular highlight.

Ambient Gel

An ambient light filter affects only ambient light hitting an object. This can also be used to give a colored tint to a white light just for selected objects. The effects of an ambient light filter are most visible in shadow areas (since they tend to be affected more by ambient light than areas illuminated by directional lights).

Directional Gel

Like an ambient light filter, this can be used to give a colored tint to a white light just for selected objects.

Fresnel

Visibility

Highlight Opacity

Note. This value should match color opacity if you want both the surface opacity and the specular's opacity to have the same value.

Facing Control

• Front renders only the faces whose normals face the camera.
• Back renders only the faces whose normals face away from the camera.
• Both renders both front and back faces.

Smooth Shade?

Note. When using the Phong, Blinn, or Cook shading models, render the scene with Smooth Shade selected.

Light Group

Note: To make a light affect one object but not another, you must first assign that light to a light group, then use that light group in the material you use to render the object.

Mapping Attributes (N-Render)

By using mapping, you can substantially increase the visual interest of rendered objects. When you do mapping, you are in essence laminating an image to the surface of an object. Any image in TIFF, TPX, or SGI format can be used as a source image for mapping. For example, you can use frame grabbed, painted, rendered, or algorithmically derived images.

N-Render supports five different types of maps, all of which are discussed later in this chapter:

• Texture mapping
• Opacity mapping
• Bump mapping
• Reflectance mapping
• Refraction mapping

Sample Maps Directory

/usr/local/ngc/presets/maps

Note. This directory is read only, so you won't accidentally erase any maps. Store any maps you create to a different directory.

Visualizing the Mapping Process

First, you have to decide how to line up the pattern of the paper with the object. Perhaps you want to align a particular motif with some dominant feature of the object. You might, for instance, want the image of Santa Claus on the wrapping paper to end up on the top of the package.

You must also decide how to tuck and fold the excess paper so the package looks neatly wrapped and the pattern lines up in such a way that it appears to match across the seams. When you map with N-Render, you can stretch your "wrapping paper" quite a bit, almost as if it were rubber. Of course, if you stretch your "paper," you also stretch the "pattern" in the same way as you might distort an image printed on a balloon when you inflate the balloon. Further, you can stretch one part of your "paper" more than others and get still other effects. Imagine a wrapping-paper image of Santa Claus, for example, acquiring oversized, pointed ears like those of his elfin helpers.

You can map a 2D image with no distortion, but only to the three following geometric primitives:

• the outside of a cylinder
• the outside of a cone
• the face of a plane

Mapping to any other surface induces some degree of distortion. This distortion can take the form of unequal scaling (whereby equally sized areas on the map are unequal on the mapped surface) or unequal orientation (whereby angles are not preserved in the mapping process; right angles, for example, become acute or oblique angles). The introduction of distortion is referred to as the general cartographer's problem because it arises in any attempt to project a spherical earth to a flat map.

Because the source image is of finite resolution, an image tends to blur when the mapping process severely distorts it. Blurring can also occur when the texture is mapped to a surface whose projected screen area is greater than the texture map itself.

Blurring can also occur on a texture-mapped object that is severely distorted by perspective. A prime example is a checkerboard placed so that its left and right edges appear to converge at infinity. At some point before the virtual horizon, the board blurs to gray.

Texture Mapping

Figure 3.7 Brick texture applied to sphere

Opacity Mapping

Figure 3.8 Brick texture map and ringed opacity map applied to sphere

Bump Mapping

The silhouette edge of a bump-opacity-mapped surface is still a polygonal edge; the true geometry is not altered, only the shader's "perception" of it. The illusion of surface texture is frequently strong enough to overcome this limitation. In addition, because bump-opacity mapping mimics fine-scale geometry, the rendered image can have significant amounts of specular aliasing as the simulated "facets" catch sharp highlights. You can modify the "depth" of these facets through the Attributes Editor.

Figure 3.9 Dot pattern bump map applied with texture to create "golf ball" effect

Texture maps and bump maps automatically have opacity maps associated with them (based on the alpha channel of the mapped image-see the section "Use Map Alpha," on page 3-29).

Reflection Mapping

Figure 3.10 Checkerboard pattern applied as reflection map at 50% opacity

Refraction Mapping

Figure 3.11 Checkerboard pattern applied as refraction map at 50% opacity

Both map types enable you to make the image reflected back to the viewer a "world view" of the object's immediate environment. You would expect the chrome bumper of an automobile parked by a stand of trees, for example, to reflect some portion of the image of the trees.

Reflection and refraction maps do not need mappers, since the surface geometry of the object determines how the map appears on the surface.

N-Render Image Mapping Parameters

Table 3.2 shows which parameters can be specified for each type of map; each of these attributes is described in more detail on the pages that follow.

Table 3.2 Mapping parameters

Characteristic	Texture	Opacity	Bump	Reflection	Refraction
Map	·	·	·	·	·
Opacity	·	·	·	·	·
Brightness	·	·	·	·	·
Depth			·
UV Scale	·	·	·	·	·
UV Offset	·	·	·
UV Rotate	·	·	·
Clip Texture?	·	·	·	·	·
Shader	·	·	·	·	·
Shader Sample Limit	·	·	·	·	·
Clipping Range?	·	·	·	·	·
Use Alpha?	·	·	·	·	·
Boundary	·	·	·	·	·
Color Scale	·	·		·	·
Background Scale				·	·
Index					·

Map

• (CLICK-L) in the text box, then use the browser which appears to select an image file.

Opacity

Note. This attribute should not be confused with an opacity map, which controls opacity of the object. This attribute affects only the transparency of the applied map.

Figure 3.12 Left, sphere with texture map of 50% opacity; right, with 100% opacity (map is shown in upper left corner)

Opacity is expressed as a value between 0 and 1, with values of 0 completely transparent and 1 completely opaque.

Brightness

Figure 3.13 Left, sphere with brightness of 1.0; right, with brightness of 2.0

UV Scale

Figure 3.14 Changes in UV scale: left 3,1; right 3,3

• The sphere on the left shows only the U scale bumped to 3; note the pattern repeats as it wraps "left to right" around the sphere.
• The sphere on the right shows both the U and V scale bumped to 3. This time, the pattern repeats both horizontally and vertically.

UV Offset

Figure 3.15 Changes in UV offset: first 0,0; second .25,0; third 0,.25, fourth .25,.25

Figure 3.15 shows how different offset values affect mapping of an image onto a surface; in this case, a texture applied through a planar mapper to a lamina:

• The first lamina shows the original lamina, with the map starting at the origin.
• The second lamina shows the U offset bumped to .25.
• The third lamina shows the V offset bumped to .25.
• The fourth lamina shows both the U and V offsets modified.

Figure 3.16 Left, unmodified UV Offset, right, with a negative U value of .3

UV Rotate

Figure 3.17 Changes in UV rotate: left, 0 degrees; middle, -45 degrees; right, 90 degrees

The map is pinned at the 0,0 UV before it is rotated.

• Negative values rotate the map in a clockwise direction.
• Positive values rotate the map in a counter-clockwise direction.

Figure 3.18 Left, original; right, rotated 25 degrees

Clip Texture?

• Upper Left specifies the offsets (measured from 0,0) at which the clipping begins.
• Lower Right specifies the offset (measured from 0, 0) at which the clipping ends.
• Diffuse Range specifies how smooth the transition should be in the u and v directions respectively (the number of pixels over which a gradient is created, in which the map fades completely out). Higher values produce softer edges.

Figure 3.19 Clip map applies only a subportion of the image file to the object or face part

This feature can be used, for example, to clip the edges from a map that has been applied through a mapper that is larger than the object.

Shader

• Point maps textures directly onto the surface, with no post-filtering.
• Jitter maps textures onto the surface, randomizing with a matrix of size specified in Sample Limit.
• Summed maps texture onto the surface using a mipmap technique.
• Sampling maps opacity onto the surface, using an average pixel value within a matrix of size specified in Sample Limit.

(CLICK-L) on shader, then select the sampling method you want to use from the pop-up that appears.

Note. Using a higher quality shader typically requires longer image rendering time.

Clipping Range

The two values specify the minimum and maximum distance between which maps are applied. Once an object moves out of the specified range, maps are no longer applied to the object.

This feature can be used to make objects that move far away in the scene (where they require less detail) render faster.

Use Map Alpha

• Yes indicates that you want to use the matte channel. Only the portion of the image that has a matte is applied to the object or face part. Note also that the matte's opacity is considered when applying the map.
• No ignores the matte channel saved with the image, applying the entire image to the object or face part.

Figure 3.20 The map and alpha channel used on the sphere; left, with map alpha off (ignoring the matte), right, with it on (using only that portion of the matte with a matte)

Boundary

Consider the application of the following texture map:

Figure 3.21 Sample texture map

• STD maps coordinates cyclically, causing the map to repeat as necessary.
• U applies the mapper by mirroring the coordinates as required along the U axis.
• V applies the mapper by mirroring the coordinates as required along the V axis.
• UV applies the mapper by mirroring the coordinates as required along both the U and V axes.
• Const applies the mapper by extending the edges of the map.

The map boundary can strongly affect the appearance of the rendered object. For example, consider the texture map in Figure 3.21 as applied through a planar mapper to the same lamina, using different Map Boundary techniques:

Figure 3.22 Sample of different map boundary parameters; in order, STD, U, V, and UV map boundary

Color Scale

Modifies the color of the map applied to the object. The color specified works like a filter applied to the map, so that it takes on a tint of the specified color.

Figure 3.23 Color scale-grid behind spheres with original texture map; spheres using yellow and blue color scales

Background Color

If you are using a partially opaque reflection or refraction map, N-Render needs to know what "color" to use to give the object a correct appearance.

The calculated background color for any reflection or refraction mapping.

Figure 3.24 Two yellow spheres. Left, with 50% opacity reflection map, and white background color; right, with 10% opacity reflection map, and magenta background color.

Depth

Controls the steepness of the bump texture walls. Bump depth is expressed using both U and V values; higher values cause the texture to appear bumpier. Both U and V coordinates can be specified, so you can make either the vertical or horizontal "bumps" more prominent. A higher U value accentuates the horizontal bumps; a higher V value accentuates the vertical bumps.

U and V values may be between the values of -10 and 10.

• If using a positive value, the black areas of the applied map appear to project outward from the mapped object (like bumps).
• If using a negative value, the black areas of the applied map appear to project inward onto the mapped object (like craters).

Figure 3.25 Apparent effect of positive and negative bump depth values

Figure 3.26 Left, bump map using positive values; right, bump map using negative values

Increasing the value in either direction makes the bumps more prominent, as shown in Figure 3.27.

Figure 3.27 Left, bump map value of 1.0; right, bump map value of 3.0

Index

Used only with refraction maps, this value modifies how the refraction map is applied to the object. A higher value causes more of the "refracted" scene to be applied to the object. To use this, you'd probably want to use a map of the rendered scene itself as your map.

The example in Figure 3.29 was created using the following map:

Figure 3.28 Sample map

The map is inverted and applied to the object as shown in Figure 3.29:

Figure 3.29 Modifying the refraction index; left, 1.33; right 2.0

Effects Attributes (N-Render)

Oblique Effects?

Figure 3.30 Oblique effects

(CLICK-L) on Yes to display the oblique effects attributes.

Note. If you are using oblique effects when creating a material, you may need to modify shadow lights used in rendering a scene that includes semi-opaque objects. Changing an object's transparency does not affect the intensity of the shadow cast by that object; you must modify the shadow light's brightness for the shadow to look realistic.

Diffuse

• In determines the diffusion value for the object at its center.
• Out determines the diffusion value for the object at its outside.
• Exp determines the rate of change in opacity diffusion from center to outside.

Opacity

• In determines the opacity of the object at its center.
• Out determines the opacity of the object at its outside.
• Exp determines the rate of change in opacity from center to outside.

Figure 3.31 Left, sphere with no oblique effects; right, with opacity oblique effects. Note the edges of the sphere on the right are more opaque than the center of the sphere.

Specular

• In determines the opacity of the highlight at its center.
• Out determines the opacity of the highlight at its outside.
• Exp determines the rate of change in opacity for the specular component from center to outside.

Higher values create a more opaque highlight.

Reflect

• In determines the transparency of the map at its center.
• Out determines the transparency of the map at its outside.
• Exp determines the rate of change in for the reflection map from center to outside.

Refract

• In determines the transparency of the map at its center.
• Out determines the transparency of the map at its outside.
• Exp determines the rate of change in for the refraction map from center to outside.

Use Fog?

Select Yes to use fog, then modify the parameters below to define its effects.

Fog Limit

At the minimum distance, the fog has an opacity of zero; at the maximum distance and beyond, it has an opacity of 100%. Objects moved toward the maximum distance appear to disappear into a fog of the specified color.

Figure 3.32 Fog limits. a is the distance from the camera at which the fog starts; b the range over which the fog effect increases from 0% to 100%; objects in "c" are enveloped in the fog at 100%

Figure 3.33 Left, octahedron with no fog effect; right, with partially past minimum fog limit

Use Default Color?

Copyright © 1996, Nichimen Graphics Corporation. All rights reserved.