3ds Max 9 Bible

Lofting is a term that comes from the shipbuilding industry. It describes a method for building ships that creates and positions the cross sections and then attaches a surface or skin along the length of the cross sections.

To create a Loft object, you need to have at least two spline shapes: one shape that defines the path of the Loft and a second shape that defines its cross section. After the shapes are created, select the Create Compound menu command. A Loft button is enabled if two or more splines are present in the viewport.

Using the Get Shape and Get Path buttons

After you click the Loft button, the Creation Method rollout displays the Get Path and Get Shape buttons, which you use to specify which spline is the path and which spline is the cross section. Select a spline, and then click either the Get Path button or the Get Shape button. If you click the Get Shape button, the selected spline is the path and the next spline shape you select is the cross section. If you click the Get Path button, the selected spline is the shape and the next spline shape you select is the path.

When creating a Loft object with the Get Shape and Get Path buttons, you can specify either to Move the spline shape or to create a Copy or an Instance of it. The Move option replaces both splines with a Loft object. The Copy option leaves both splines in the viewport and creates a new Loft object. The Instance option maintains a link between the spline and the Loft object. This link enables you to modify the original spline. The Loft object is updated automatically.

The vertex order of the path spline is important. The Loft object is created starting at the vertex numbered 1.

Controlling surface parameters

All Loft objects include the Surface Parameters rollout. Using this rollout, you can set the smoothing of the Loft object with two different options: Smooth Length and Smooth Width. You can use the Mapping options to control the mapping of textures by setting values for the number of times the map repeats over the Length or Width of the Loft. The Normalize option applies the map to the surface evenly or proportionately according to the shape's vertex spacing. You can set the Loft object to automatically generate Material and Shape IDs, and you can specify the output of the Loft to be either a Patch or Mesh.

Changing path parameters

The Path Parameters rollout, shown in Figure 18.16, lets you position several different cross-sectional shapes at different positions along the Loft path. The Path value indicates either the Distance or Percentage along the path where this new shape should be located. The Snap option, if turned on, enables you to snap to consistent distances along the path. The Path Steps option enables you to place new shapes at steps along the path where the vertices are located. Each path will have a different number of steps depending on its complexity.

Figure 18.16: The Loft compound object rollouts

The viewport displays a small yellow X at the location where the new cross-sectional shape will be inserted. At the bottom of the rollout are three buttons, which are illustrated and described in Table 18.1.

Setting skin parameters

The Skin Parameters rollout includes many options for determining the complexity of the Loft skin. You can specify whether to cap either end of the Loft using the Cap Start and/or Cap End options. The caps can be either Morph or Grid type.

This rollout also includes the following options for controlling the look of the skin:

• Shape and Path Steps: Sets the number of segments that appear in each spline's cross-sectional shape and between each division along the path. The straight segments are ignored if the Optimize Path option is selected.

• Optimize Shapes and Paths: Reduces the Loft's complexity by deleting any unneeded edges or vertices.

• Adaptive Path Steps: Automatically determines the number of steps to use for the path in order to maintain a smooth curve.

• Contour: Determines how the cross-sectional shapes line up with the path. If this option is enabled, the cross section is aligned to be perpendicular to the path at all times. If disabled, this option causes the cross-sectional shapes to maintain their orientation as the path is traversed.

• Banking: Causes the cross-section shape to rotate as the path bends.

• Constant Cross-Section: Scales the cross-sectional shapes in order to maintain a uniform width along the path. Turning off this option causes the cross sections to pinch at any sharp angles along the path.

• Linear Interpolation: Causes straight linear edges to appear between different cross-sectional shapes. Turning off this option causes smooth curves to connect various shapes.

• Flip Normals: Used to correct difficulties that would appear with the normals. Often the normals are flipped accidentally when the Loft is created.

• Quad Sides: Creates four-sided polygons to connect to adjacent cross-section shapes with the same number of sides.

• Transform Degrade: Makes the Loft skin disappear when subobjects are transformed. This feature can help you better visualize the cross-sectional area while it is being moved.

The Display options at the bottom of the Skin Parameters rollout give you the choice of displaying the skin in all viewports or displaying the Loft skin only in the viewports with shading turned on.

Tutorial: Designing a slip-proof hanger

As an example of creating a Loft object with different cross-sectional shapes, we design a new hanger that includes some rough edges along its bottom section to keep slacks from sliding off.

To design a hanger Loft object with different cross sections, follow these steps:

1. Open the  Lofted slip-proof hanger.max file from the Chap 18 directory on the DVD. This file includes a spline outline of a hanger and two simple shapes.

2. Select the hanger spline, and choose the Create Compound Loft menu command.

3. In the Creation Method rollout, click the Get Shape button and then click the small circle shape (make sure that the Copy option is selected).

   This lofts the entire hanger with a circular cross section.

4. In the Path Parameters rollout, select the Path Steps option. A dialog box appears warning that this may change the relocate shapes. Click Yes to continue. Increment the Path value until the yellow X marker in the viewport is positioned at the beginning of the hanger's bottom bar (at Step 53 for this tutorial). Click the Get Shape button again, and click the small circular shape again.

   This extends the circular cross section from the start at Step 0 to Step 53.

5. Increment the Path value by 1 to Step 54, click the Get Shape button, and select the star shape. This makes the remainder of the hanger use a star-shaped cross section. Increment the Path value again to the end of the hanger's bottom bar (at Step 60), click the Get Shape button, and select the star shape again to end the star cross section.

   Note

   If you forget to start and end a section with the same cross section, the loft blends between the two different cross sections.

6. In the Path Parameters rollout, increment the Path value a final time to Step 61, click the Get Shape button, and click the circular shape. Click the Pick Shape icon button at the bottom of the Path Parameters dialog box to change the cross section of the hanger to the end of the path. Right-click in the viewport to exit Get Shape mode.

Figure 18.17 shows the finished designer hanger.

Figure 18.17: A lofted hanger created with two different cross-sectional shapes

Deforming Loft objects

When you select a Loft object and open the Modify panel, the Deformation rollout appears. This rollout includes five buttons that let you Scale, Twist, Teeter, Bevel, and Fit the cross-section shapes along the path. All five buttons open similar graph windows that include control points and a line that represents the amount of the effect to apply. Next to each button is a toggle button with a light switch on it. This button enables or disables the respective effect.

The Deformation window interface

All five deformation options use the same basic window and controls. The lines within the window represent the length of the path. As an example of the Deformation window interface, Figure 18.18 shows the Scale Deformation window.

Figure 18.18: The Deformation dialog box interface lets you control the cross section over the length of the path

Dragging the curve directly can modify the deformation curve. You can also insert control points at any location along the curve. These control points can be one of three different types: Corner, Bézier Corner, or Bézier Smooth. Bézier type points have handles for controlling the curvature at the point. To change the point type, select the point and right-click. Then make your selection from the pop-up menu. The end points must always be either Corner or Bézier Corner type.

To move a control point, select and drag it or enter a horizontal and/or vertical value in the fields at the bottom of the window.

Table 18.2 describes the buttons at the top of the Deformation window.

At the bottom of the Deformation dialog boxes are two value fields. The value fields display the X and Y coordinate values for the currently selected point. The navigation buttons enable you to pan and zoom within the dialog box.

Figure 18.19 and Figure 18.20 show each of the various deformation options applied to a lofted column.

Figure 18.19: The Loft compound object deformation options: Scale, Twist, and Teeter

Figure 18.20: The Loft compound object deformation options: Bevel and Fit

Scale Deformation

The Scale Deformation window can alter the relative scale of the Loft object at any point along its path. This window includes two lines: one red and one green. The red line displays the X-axis scale, and the green line displays the Y-axis scale. By default, both lines are positioned equally at the 100 percent value. Specifying a value greater than 100 percent increases the scale, and specifying a value less than 100 percent has the opposite effect.

Twist Deformation

The Twist Deformation rotates one cross section relative to the others and can be used to create an object that spirals along its path. This option is similar to the Banking option, which can also produce rotations about the path.

The Twist Deformation window includes only one red line representing the rotation value. By default, this line is set to a 0-degree rotation value. Positive values result in counterclockwise rotations, and negative values have the opposite effect.

Teeter Deformation

Teeter Deformation rotates a cross section so that its outer edges move closer to the path. This is done by rotating the cross section about its local X-axis or Y-axis. The result is similar to that produced by the Contour option.

The Teeter Deformation window includes two lines: one red and one green. The red line displays the X-axis rotation, and the green line displays the Y-axis rotation. By default, both lines are positioned equally at the 0 degree value. Positive values result in counterclockwise rotations, and negative values have the opposite effect.

Bevel Deformation

Bevel Deformation bevels the cross-section shapes. The Bevel Deformation window includes only one red line representing the amount of bevel applied. By default, this line is set to a 0 value. Positive values increase the bevel amount, which equals a reduction in the shape area, and negative values have the opposite effect.

You can also use the Bevel Deformation window to select three different types of beveling: Normal, Adaptive Linear, and Adaptive Cubic. Table 18.3 shows and describes the buttons for these three beveling types. You can select them from a flyout at the right end of the window.

Fit Deformation

The Fit Deformation window, shown in Figure 18.21, lets you specify a profile for the outer edges of the cross-section shapes to follow. This window includes two lines: one red and one green. The red line displays the X-axis scale, and the green line displays the Y-axis scale. By default, both lines are positioned equally at the 100 percent value. Specifying a value that is greater than 100 percent increases the scale, and specifying a value less than 100 percent has the opposite effect.

The Fit Deformation window includes ten buttons unique to it that are used to control the profile curves. These buttons are illustrated and described in Table 18.4.

Modifying Loft subobjects

When you select a Loft object, you can work with its subobjects in the Modify panel. The subobjects for a Loft include Path and Shape. The Path subobject opens the Path Commands rollout. This rollout has only a single button-Put-for creating a copy of the Loft path. If you click this button, the Put To Scene dialog box appears, enabling you to give the path a name and select to create it as a Copy or an Instance.

If your path is created as an Instance, you can edit the instance to control the Loft path.

Figure 18.21: A Loft object with Fit Deformation applied

The Shape subobject opens the Shape Commands rollout. This rollout also includes a Put button along with some additional controls. The Path Level value adjusts the shape's position on the path. The Compare button opens the Compare dialog box, which is discussed in the following section. The Reset button returns the shape to its former state before any rotation or scaling has taken place, and the Delete button deletes the shape entirely.

The Shape Commands rollout also includes six Align buttons for aligning the shape to the Center, Default, Left, Right, Top, and Bottom. For the Loft object local coordinates, Left and Right move the shape along the X-axis, and Top and Bottom move it along the Y-axis.

Comparing shapes

The Compare dialog box superimposes selected cross-sectional shapes included in a Loft object on top of one another to check their center alignment. The button in the upper-left corner is the Pick Shape button. This button lets you select which shapes to display in the dialog box. The button to its right is the Delete Shape button, for removing a shape from the dialog box. Figure 18.22 shows the Compare dialog box with the two shapes from the pillar example selected. Notice that the first vertices on these two shapes are in different locations. This causes the strange twisting at both the top and bottom of the pillar.

Figure 18.22: You can use the Compare dialog box to align shapes included in a Loft

While the Compare dialog box is open, the Align buttons in the Shape Commands rollout are still active and can be used to move and position the shapes. The first vertex on each shape is shown as a small square. If these vertices aren't correctly aligned on top of one another, then the resulting Loft object will have skewed edges. The lower-right corner of the dialog box includes buttons to View Extents, Pan, Zoom, and Zoom Region.

Editing Loft paths

The original shapes that were used to create the Loft object can be edited at any time. These updates also modify the Loft object. The shapes, if not visible, can be selected using the Select by Name button. The shapes maintain their base parameters, or they can be converted to an Editable Spline.

Tutorial: Creating drapes

Modeling home interiors is a task commonly performed by professional architects and interior designers, but creating the drapes can be tricky. In this tutorial, we create some simple drapes using a Loft object.

To create drapes using a Loft object, follow these steps:

1. Open the  Lofted drapes.max file from the Chap 18 directory on the DVD. This file contains two splines that can be used to create the loft.

2. Select the straight line spline, and select the Create Compound Loft menu command. In the Creation Method rollout, click the Get Shape button and then click the cross-section spline.

3. Open the Modify panel, and under the Skin Parameters rollout, turn off the Contour and Banking options.

4. Use the Deformation functions to add more control to the drapes, such as tying them together as shown in Figure 18.23.

Figure 18.23: Drapes that have been modeled using a Loft object

Loft objects versus surface tools

You can create compound loft objects completely from 2D shape splines: One open spline is typically used as the Loft path, and other, closed splines are used as the cross sections. You can have several different cross sections, and these can change as you travel the path. Loft cross sections aren't required to have the same number of vertices, and you can modify the scale and rotation of the cross sections with the Deformation options.

The surface tools, which include the CrossSection and Surface modifiers, provide another way to model that is similar to lofting. The CrossSection modifier takes several cross-section shapes and connects their vertices with additional splines to create a spline framework. You can then use the Surface modifier to cover this framework with a skin.

Although similar in nature, Loft objects and the surface tools have different subtleties and strengths.

One difference is that the CrossSection modifier connects spline cross sections according to their order. This can cause strange results if the order is incorrect. A Loft always follows a path, so the cross-section order isn't a problem.

Another difference is that surface tools give you more control over the surface of a created object. Because the underlying structure is a series of splines, you can add new branches and objects without much difficulty. This can be hard to do with Loft objects.

As a general guideline, Loft objects are better suited to modeling rigid objects with relatively uniform cross sections, whereas the surface tools are better for modeling more organic model types.