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Using the Unwrap UVW modifier

The Unwrap UVW modifier lets you control how a map is applied to a subobject selection. It can also be used to unwrap the existing mapping coordinates of an object. You can then edit these coordinates as needed. You can also use the Unwrap UVW modifier to apply multiple planar maps to an object. You accomplish this task by creating planar maps for various sides of an object and then editing the mapping coordinates in the Edit UVWs interface.

The Unwrap UVW modifier lets you control precisely how a map is applied to an object. The Unwrap UVW modifier has a single subobject mode named Select Face. In this subobject mode, you can select face subobjects, and the same face selection is displayed in the Edit UVWs interface and vice versa. In the Modify panel, you’ll find two rollouts: Selection Parameters and Parameters. The Selection Parameters rollout includes a button with a plus sign and one with a minus sign. These buttons grow or shrink the current selected subobject selection. You can also select to Ignore Backfacing, Select by Element (instead of faces), set the Planar Angle, or select by Material ID or Smoothing Group.

The Edit UVWs interface

The Parameters rollout includes a button named Edit. This button opens the Edit UVWs interface, shown in Figure 23-5 for a simple cube. You can also load and save the edited mapping coordinates using the Save and Load buttons in the Parameters rollout, and the Reset UVWs button resets all the mapped coordinates. Saved mapping coordinate files have the .UVW extension.

Figure 23-5: The Edit UVWs interface lets you control how different planar maps line up with the model.

Table 23-1 shows and describes the buttons in the Edit UVWs dialog box.

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Table 23-1: Edit UVW Interface Buttons

Buttons	Name	Description
	Move,	Moves the selected vertices when
	Move Horizontal,	dragged.
	Move Vertical
	Rotate	Rotates the selected vertices when
		dragged.
	Scale, Scale	Scales the selected vertices when
	Horizontal,	dragged.
	Scale Vertical
	Freeform Mode	Displays a gizmo that you can use
		to transform the subobject
		selection.
	Mirror Horizontal,	Mirrors or flips the selected
	Mirror Vertical,	vertices about the center of
	Flip Horizontal,	the selection.
	Flip Vertical
	Show Map	Toggles the display of the map in
		the dialog box.
	Coordinates	Displays the vertices for the UV,
		UW, and WU axes.
	Pick Texture	Displays a drop-down list of all the
	drop-down list	maps applied to this object. You
		can display new maps by using the
		Pick Texture option.
	U, V, W values	Displays the coordinates of the
		selected vertex. You can use these
		values to move a vertex.
	Lock Selected	Locks the selected vertices and
	Vertices	prevents additional vertices from
		being selected.
	Filter Selected	Displays vertices for only the
	Faces	selected faces.
	All IDs	Filters selected material IDs.
	drop-down list

The buttons in the lower-right corner of the Edit UVWs dialog box work just like the Viewport Navigation buttons described in earlier chapters.

Many of the commands found in the menus can also be found in the pop-up Options interface, shown in Figure 23-6. You can enable Soft Selection using this dialog box. In the Bitmap Options section, you can specify the resolution of the bitmap. You can expand this interface by clicking on the Show Options button.

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Figure 23-6: The Options pop-up interface includes many of the same features as the menus.

The File menu can also be used to load (Alt+Shift+Ctrl+L), save, and reset UV coordinates. The Edit menu lets you specify the mode to use to transform subobject selections. These modes include Move (Q), Rotate (Ctrl+R), Scale, and Freeform, which lets you use the gizmo to transform subobjects. The Edit menu also includes Copy and Paste and a Paste Weld command. The Copy and Paste commands let you copy a mapping and paste it to another set of faces. The Paste Weld command welds vertices as it pastes the mapping.

The gizmo is simply a rectangle gizmo that surrounds the current selection. Move the selection by clicking in the gizmo and dragging; Shift+dragging constrains the selection to move horizontally or vertically. The plus sign in the center marks the rotation and scale center point. Scale the selection by dragging on one of its handles. Ctrl+dragging on a handle maintains the aspect ratio of the selection. Click and drag the middle handles to rotate the selection. Ctrl+dragging snaps to 5-degree positions, and Alt+dragging snaps to 1-degree positions.

Within the Edit UVWs interface, you can select vertices, edges, or faces. The Select Get Selection From Viewport (Alt+Shift+Ctrl+P) menu command lets you select and transfer the selection from the viewports, or you can convert selections between vertices, edges, and faces. Subobjects that are selected in one planar map are also highlighted in the other planar maps. This makes it easy to stitch elements together.

The Tools menu includes commands for flipping, mirroring, welding, breaking, and detaching subobjects. The Tools Stitch Selected menu command lets you stitch mapped segments together into a single cluster, and the Pack UVs menu command lets you combine UVs into a smaller space. Packed UVs are easy to move and work with because they use a smaller resolution bitmap. Within the Pack dialog box, the Spacing value sets the amount of space between each segment, and the Normalize Clusters option fits all clusters into the given space. The Rotate Clusters option allows segments to be rotated to fit better, and the Fill Holes option places smaller segments within open larger segments.

The Tools Sketch Vertices command lets you select vertices by dragging over them. The vertices can then be aligned to a shape including Line, Circle, Box, or Freeform. You can also set the cursor size used to select vertices.

The Mapping menu includes three auto-mapping options: Flatten, Normal, and Unfold Mapping. The Flatten Mapping option breaks the mesh into segments based on the angle between adjacent faces. This option is good for objects that have sharp angles like a robot or a machine. Figure 23-7 shows a plastic bottle with Flatten Mapping applied.

The Normal Mapping option lets you select to map a mesh using only specific views, including Top/Bottom, Front/Back, Left/Right, Box, Box No Top, and Diamond. These views are based on the direction of the normals from the faces of the mesh. It is helpful for thin models like butterfly wings or a coin.

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Figure 23-7: The Flatten Mapping option displays every part of a model as a separate segment.

The Unfold Mapping option is unique because it starts at one face and slowly unwraps all the adjacent faces into a single segment if possible. Figure 23-8 shows a simple cube that has been unwrapped using this method. The advantage of this mapping is that it results in a map with no distortions. It includes two options: Walk to Closest Face and Walk to Farthest Face. You’ll almost always want to use the Walk to Closest Face option.

The Options Advanced Options (Ctrl+O) menu command opens the Unwrap Options dialog box, shown in Figure 23-9, and lets you set the Line and Selection Colors as well as the preferences for the Edit UVWs dialog box. You can load and tile background images at a specified map resolution or use the Use Bitmap Resolution option. There is also a setting for the Weld Threshold and options to constantly update, show selected vertices in the viewport, and snap to the middle pixel.

Tutorial: Controlling the mapping of a covered wagon

The covered wagon model created by Viewpoint Datalabs is strong enough to carry the pioneers across the plains, but you can add a motivating slogan to the wagon using the Unwrap UVW modifier. In this tutorial, we add and edit the mapping coordinates for the covered wagon using the Unwrap UVW modifier.

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Figure 23-8: The Unfold Mapping option splits the model and unfolds it by adjacent faces into a single segment.

Figure 23-9: In the Unwrap Options dialog box, you can set the preferences for the Edit UVWs dialog box.

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To control how planar maps are applied to the side of a covered wagon, follow these steps:

1.Open the Covered wagon.max file from the Chap 23 directory on the CD-ROM.

This file includes a covered wagon model. The Chap 23 directory also includes a 256×256 image, created in Photoshop, of the paint that we want to apply to its side. The file is saved as Oregon or bust.tif (note that the spelling in the file is rough).

2.With the covered section selected, choose Modifiers UV Coordinates Unwrap UVW. In the Parameters rollout, click the Edit button.

The Edit UVWs interface opens.

3.In the Edit UVWs interface, choose Mapping Normal Mapping. In the Normal Mapping dialog box, select the Left/Right Mapping option from the drop-down list and click OK.

The left and right views of the wagon’s top are displayed in the Edit UVWs interface.

4.From the drop-down list at the top of the interface, select the Pick Texture option. The Material/Map Browser opens. Double-click on the Bitmap option, and select the Oregon or bust.tif image from the Chap 23 directory on the CD-ROM.

The texture appears in the window.

5.Drag the mouse over all the vertices for the lower half of the wagon’s cover, and press the Delete key to delete all those vertices.

This represents the half of the top that won’t be painted.

6.Then select all the remaining vertices and, with the Move tool, drag them to the center of the Edit UVWs window. Click and hold over the Scale tool, and select the Vertical Scale tool. Then drag in the window to vertically scale the vertices until they fit over the texture. Then horizontally scale the vertices slightly until the background texture is positioned within the wagon’s top.

Figure 23-10 shows the covered wagon with the mapped bitmap.

7.Press the M key to open the Material Editor. Click on the mapping button next to the Diffuse color, and double-click on the Bitmap type in the Material/Map Browser. Then select the Oregon or bust.tif file from the Chap 23 directory on the CD-ROM. Then apply this material to the covered wagon top. Click the Show Map in Viewport button (the small checkerboard cube icon) to see the map on the covered wagon.

Figure 23-11 shows the results of the new mapping coordinates.

Relaxing vertices

If your mapping coordinates are too tight and you’re having a tough time moving them, you can use the Relax tool (found in the Tools menu of the Edit UVW interface) to equally space the vertices. This tool works like the Relax modifier, pushing close vertices away and pulling far vertices closer together. Selecting this menu option opens the Relax Tool dialog box, shown in Figure 23-12. Amount is how aggressive the movement of the vertices are, and Iterations is the number of times to apply the relax algorithm. You also have options to Keep Boundary Points Fixed and Save Outer Corners.

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Figure 23-10: The Edit UVWs interface lets you transform the mapping coordinates by moving vertices.

Figure 23-11: The position of covered wagon’s texture map has been set using the Unwrap UVW modifier.