
	Patches: Matching Boundaries

As mentioned above, patch dimensions are derived from the number of Divisions on boundary curves. When a patch is created, or refitted, its U and V dimensions are calculated from the maximum number of divisions on each pair of opposing boundaries.

Figure 75. Matching Divisions

Patches are considered to be matched when they have the same number of U or V grids at an adjacent boundary (see Figure 75). Whenever adjacent boundaries are matched, the curve turns from blue to magenta (i.e. purple).

Patches must be matched if you want them to be made tangent (see the "Tangency" section below), and Stitching will only work across matched boundaries.

Figure 76. Matching Divisions: 1 To N

Patches are also matched when one has grids that are a multiple of the other's, such as 1 to 2, or 1 to 3, and so on (see Figure 76). When this "1 To N" matching occurs, the curve is drawn with a dashed line.

Figure 77. 1 To 3 Matching At Wrist

"1 To N" matching can can be very useful when you want reduced or increased density of patches in different parts of a polymesh. For example, you might want denser patches in a hand, but have less dense patches going up the arm (see Figure 77).

Patch Flow

If a boundary curve has one or more shape points along its length, and adjacent patches are matched, then the divisions points can be used to modify the patch flow.

Figure 78. Using Divisions To Change Patch Flow

Figure 78 and Figure 79 shows the gradual shifting of division points from the bottom half to the top half of the shared boundary curve. This is easily achieved by first removing a division point from the bottom half (with the <-> key), followed by the addition of a division point to the top half (with the <=> key).

Figure 79. But Taking It Too Far

The last image in the sequence shows the process taken to the extreme. Even though the UV grid lines look fine, the surface begins to fold back on itself. This is because its a uniform bspline patch, and the spacing of knots needs to be kept reasonably uniform for best results.

Bunching

New in v3 is the Bunching tool. Division points can be pushed to either end of a curve segment with the <[> and <]> keys.

Figure 80. Division Point Bunching

Figure 80 illustrates one use of the bunching tool. The image on the left shows the default even spacing for each patch. The nearly 4 to 1 difference in knot spacing across the boundary would cause problems if these two patches were stitched.

The image on the right shows a gradual change in knot spacings across the boundary. This was achieved by bunching, to the right, the div points of the top and bottom boundaries of each patch. These two patches can now quite safely be stitched.

Tangency

By default, patches are tangent at matched boundaries. To turn off tangency at selected boundaries, move the mouse pointer over the boundary, then hit the <t> key. That section of curve will then be drawn in cyan (light blue) to indicate that the tangency has been turned off. Hit <t> again to turn the tangency back on (see Figure 81).

Figure 81. Tangency On and Off

When developing a complex network you'll probably work in stages, hiding parts that you've already done. The automatic tangency update only works on visible patches, so its likely that the hidden patches will end up being non-tangent with the visible patches. This will become obvious when you have finished, make the entire network visible, and shade the result.

At any point you can make sure that all visible boundaries are tangent by clicking on the Update button in the Patches panel.

Active Networks

By default, the network is active. This means that if changes are made to any curve, such as the number of divisions or the curve shape, then all affected patches are re-fitted.

Sometimes, if you have a lot of changes to make, it can be quicker to temporarily turn the re-fitting off. If you click the Off button in the Patches panel, then patches won't be refitted whenever you change a curve. Then, after you've made the changes, click on Rebuild and all affected patches will be refitted.

Best Fit

To improve interactivity in its normal mode of operation, CySlice sacrifices some fitting quality to gain speed. But once you have developed a network to completion, you'll want the best fit possible. To get this, click on BF in the Patches panel.