Sega Materials and Attributes

This chapter outlines briefly the attributes and parameters associated with the Sega domain in the N·World Attributes Editor.

Materials and Inheritance

Materials can be assigned to an entire object or to a selected face part of an object (a face part is a collection of faces from the object). Materials you want to use with the Sega Saturn must be defined in the Sega render domain. This domain has several properties and unique parameters, which you control with the Attributes Editor menus.

The method for creating materials is no different for the Sega domain than for any other domain. To learn how to create materials, as well as how to specify attribute inheritance from one material to another, see the Attributes Editor Reference Guide.

The Attributes Editor

Figure 3.1 Attributes Editor menu for the Sega domain.

Sega Domain Defaults

Figure 3.1 Sega domain defaults dialog.

Map Directory

The default directory from which maps are read.

Maximum Angle

The maximum angle a non-flat face can be "bent" before it is cut into two faces when sent to the Saturn.:

Figure 3.2 Cutting non-flat faces

Background Color

The color displayed behind the object during the test preview.

Preshade Object?

If set to Yes, the lights in the Default Light Group are used to preshade the object before it is sent to the Sega Saturn. See the Attributes Editor User's Guide for more information on setting up light groups.

Update Camera?

If set to Yes, the position of the camera on the Sega Saturn is updated to follow the position of the camera in the N-Geometry window.

Note. You may experience gimbal lock on the display of the Sega Saturn if you rotate the camera and look at the object straight down along the Y axis. This is an unavoidable effect often encountered in 3D simulations.

Saving Your Defaults

To save your defaults, (Click-L) on the Save Preferences button at the bottom of the window.

Sega Domain Shader Parameters

Color

Default: White

The color attribute is used for two purposes in the Sega render domain:

• To define the color of the object.
• An RGB value (color) multiplier for RGB values of any applied map.

If you apply a map over an object or part that has a color other than white, the appearance of that map is altered. For example, if you apply a red brick texture onto a yellow cube, the bricks would take on a yellowish hue (how yellow would depend on the RGB value of the yellow assigned to the cube).

Facing Control

Default: Front

• Front renders only those faces with normals facing the camera. Faces whose normals point away from the camera are not rendered.
• Both renders all faces in the scene, regardless of their orientation.

Note. The Facing Control attribute is identical to the Plane attribute in SGL terminology (and in the Saturn documentation).

Omit Face?

Default: No

• Yes keeps the polygon information for the selected faces from being sent to the Saturn when the Preview button is pressed.

For example, you might set Omit face? to Yes for faces on the back of an object.

• No sends the polygon information for the face.

Preshade

Default: Yes

• Yes shades the object or faces using existing lights for the scene before sending them to the Sega Saturn.
• No sends the object or faces using only the color of the object; any light influence is ignored, and all faces have the specified Color attribute.

Sort Control

Default: Min

The Sega maintains a z-order sort index which lets you specify which faces are to be displayed "on top". This is of significance if you have overlapping or intersecting faces.

• Min performs a z-order sort. Faces with a vertex closest to the camera are displayed on top.
• Max performs a z-order sort. Faces with a vertex furthest from the camera are displayed on top.
• Center calculates the center point for each face, then displays those faces based on the distance of those center points from the camera. Faces with center points closest to the camera are displayed on top.

Use Lights?

Default: No

This attribute, along with the Preshade attribute, determines how faces are shaded on the Sega Saturn:

Table 3.1 Interaction of Use Lights? and Preshade attributes

Preshade	Use Lights?	Result
No	No	The face color is defined by the Color attribute. No shading takes place.
Yes	No	Faces are preshaded on the SGI before being sent to the Sega Saturn, using the lights in the current N-Geometry scene.
No	Yes	Faces are shaded interactively on the Sega Saturn, using light information defined in the SGL program.
Yes	Yes	Faces are pre-shaded on the SGI before being sent to the Sega Saturn, using the lights in the current N-Geometry scene. Those preshaded faces are also shaded interactively on the Sega Saturn.

Use Clipping?

Default: No

Specifies whether or not to display vertices outside of a user-defined clipping area.

• Yes clips vertices outside of the area.
• No calculates the display for all vertices in the scene.

Smooth Shade?

Default: No

The smooth shade parameter selects either "color by vertex" or "color by face."

• Yes shades the face from each vertex on the face, producing a smoother appearance (uses the vertex normal for each vertex on the face).
• No colors the vertex by face; the face has a uniform color over the entire face (uses the face normal only).

Figure 3.3 Color by vertex vs. color by face

Draw as Mesh?

Default: No

• Yes draws the selected face as a "mesh," by drawing every other line on the face.
• No draws the face as solid.

Note. While this attribute causes the face to appear transparent, it is actually more of a "venetian blind" effect; the transparency of the drawn portion of the faces is not affected by this setting.

Drawing Mode

Default: Overwrite

Determines which of the various drawing modes available on the Sega Saturn is used to draw the face:

• Overwrite performs a z-sort on all faces, displaying those closest to the camera "on top." This is the default mode, and is described in the Sega VDP-I manual on p. 87.

Figure 3.4 Overwrite drawing mode

• Shadow draws the selected face as a shadow; this mode is described in the Sega VDP-I manual on p. 88.

Figure 3.5 Shadow drawing mode

• Semi-bright cuts the luminance value for the selected face in half.

Figure 3.6 Semi-bright drawing mode

• Semi-transparent cuts the transparency for the selected face to 50%; the color of any faces serve as RGB multipliers to determine the final appearance of the face.

Figure 3.7 Semi-transparent drawing mode

Texture Map Parameters

Figure 3.8 Sega domain texture attributes

Texture Map

Default: None

Specify the pathname for the texture map to be applied to the face, part, or body. The application of texture maps through mappers is described in more detail in the N-Render Reference Guide.

The size and number of texture maps which can be sent to the Sega Saturn are limited only by the texture map memory available.

Reuse Map?

Default: No - Only if a texture map is specified

If yes, then all faces share the same texture map. If you specify a texture map in the Texture Map field, then (Click-L) on Yes for Reuse Map, the direction field appears, with four choices.

• No Flip applies the texture map normally.
• H Flip flips the applied texture map around the horizontal axis (up/down).
• V Flip flips the applied texture map around the vertical axis (left/right).
• HV Flip flips the applied texture map both vertically and horizontally.

Note. The "flipping" is based on the face's orientation, not its relationship to the viewer.

Scale

Only if a Texture Map is specified.

• Scale lets you specify the how the map is to be scaled. You can use scaling to "fit" texture maps to faces.

Figure 3.9 Scaling texture map

Normally, the portion of the map that is applied to a face is determined by checking its uv values against those of the applied map:

u(max) - u(min) = value x width = pixels applied in u

v(max) - v(min) = value x height = pixels applied in v

.7 - .2 = .5 x 80 = 40 pixels applied in u

.9 - .2 = .7 x 40 = 28 pixels applied in v

Specifying a Scale value allows you to change the number of pixels applied to the specified face. If you wanted twice the information to be applied to the selected face, you could add a scale value of 2, which would affect the equation as follows:

.7 - .2 = .5 x 80 = 40 x 2 = 80 pixels applied in u

.9 - .2 = .7 x 40 = 28 x 2 = 56 pixels applied in v

Note. The width of the resulting map must always be divisible by 8, and must be < 505.

The height must be <256.

Sega Domain Commands

Revert

• (CLICK-L) on Revert to undo all changes made to attributes for the current material since the last time it was saved.
• (CLICK-R) on Revert to reset any local attributes to their default values.

Redisplay

• (CLICK-L) on Redisplay to redisplay the current material in the geometry window. You should do this after making changes to your materials.
• (CTRL-M) on Redisplay to update texture maps. If you've edited the image files you're using as texture maps, use this option to make sure the updated maps are used.

Reset

(CLICK-L) on Reset to reset the attached Saturn.

Preview

(CLICK-L) on Preview to send all the objects in the current scene to the Sega Saturn.

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