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A typical PC game texture budget is calculated by examining the video memory of the target machine, currently about 2 MB. That video memory must store the screen area, (about 302 KB), an offscreen draw buffer of the same size, and finally the texture memory. That limits texture memory for the entire scene to about 1.4 MB, or the size of a floppy disk. The textures are mapped into the screen area by choosing which pixels of the texture to copy into which area of the screen memory, an operation usually performed by the video card itself.

Because texture space is at a premium and takes longer to draw to the screen anyway, clever use of material color is a must. One technique is the use of vertex shading. Each vertex of a polygon may, in fact, have a different color, and when they are drawn to the screen, the shading engine creates a gradient between the vertices with different coloration. This method is growing in popularity and is completely supported by Softimage. Softimage can even convert a texture map on a polygonal mesh into vertex colors.

Figure 7.4 Two low poly vehicles, with 256*256 pixel texture maps from the Microsoft Combat Flight Simulation game, modeled and textured by David Choi. Copyright 1998 Microsoft Corp.

Figure 7.5 A very small texture sheet used to texture Microsoft low poly models for the Microsoft Combat Flight Simulation game. Texture map painted by David Choi. Copyright 1998 Microsoft Corp.

Make Mine Pink: Selecting Polygons

The Polygon Selection methods are listed in the Polygon menu cells (see Figure 7.6). Those polygons selected on a given object are highlighted in a translucent pink shade in the Wireframe views (see Figure 7.7). When you switch to the POL mode, only the selected, pink polygons are transformed by the Scale, Rotate, and Translate menu cells. Many other commands are likewise restricted to the selected group of polygons.

Figure 7.6 The Polygon menu cells in the Model module.

You can select polygons by tagging the vertices of the polygon desired and executing the Polygon->Tag Vertex command. I do not find this command useful, however. A more popular method is the Polygon->Select by Rectangle command (supra key Y), which you use by dragging a Marquee around a polygon or group of polygons. When you drag with the left mouse button, those polygons entirely within the Marquee are selected and shown in pink in the Wireframe view windows. If you use the middle mouse button, those within the Marquee are deselected, and if you use the right mouse button, they are toggled to the opposite of their previous state.

Figure 7.7 A model with selected polygons highlighted in pink.

The Select by Rectangle method selects polygons on either side of an object, so be sure to check that only those desired are highlighted before you transform the selected group.

The newest method, appearing in version 3.5, is Polygon->Select by Raycasting (supra key G). When Select by Raycasting is active, hold down the left mouse button to select the polygon directly under your pointer. Only polygons with normals pointing towards you are selected, so polygons on the backside of an object are not added to the selected group of polygons. If no polygons become selected when you use the G supra key, the normals may be inverted. When you raycast with the middle mouse button, you deselect polygons, while the right mouse button toggles polygons.


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