So far the technique for fitting multiple patches to a polymesh has been described. But in some situations it is nice to be able to fit one large patch completely over a polymesh. For example, many users prefer to fit a single patch over a face and head, radiating out from the mouth. CySlice supports the single patch approach by allowing users to fit smaller patches that are then stitched together to make larger patches.

Stitching can also be used to control the flow of knot lines within a patch. On a human figure, for example, it can be a good idea to have a single patch for each arm and leg, but you want to be able to control the flow on knot lines around elbows and knees. In CySlice this is achieved by building the arms and legs out of small patches that are then stitched together. The resulting patches then have internal shape points than can be used to control the flow of the knot lines around the joints.

Figure 82. Patches That Can Not Be Stitched

Patches will only stitch together if there is 1-to-1 matching of knots at the boundary, and if the result would be a valid NURBS patch (i.e. a topologically rectangular control grid). Figure 82 shows two groups of patches that can't be stitched together because the result wouldn't be a valid patch.

Figure 83. Patches That Can Be Stitched

Figure 83 shows the same shape curves, but filled with three sided patches, that can be stitched together. The result, shown on the right, is one large three sided patch. Figure 84 shows some more patches that can be stitched together.

Figure 84. More Patches That Can Be Stitched

The actual stitching process is very simple; first move the mouse pointer over a shared boundary, then hit the <9> key. The shape curve will turn pale to indicate a stitched boundary. Hit <9> again to turn the stitching off.

Figure 85. Patches Being Stitched

Figure 85 shows some intermediate stages of the stitching process. The top right boundary, between patches pat1 and pat2 is stitched first, creating a new patch called sti1. Next the three segments of the middle boundary are stitched. No new patches are created because the result wouldn't be a valid patch; there is still a split between patches pat3 and pat4.

Figure 86. Final Stitched Patch

That remaining boundary is then stitched (see left side of Figure 86) and a single larger patch is created (see middle).

As you can see, it doesn't matter in which order the internal boundaries are stitched. You might think you would have to first stitch pat1 to pat2, then pat3 to pat4, then stitch the two halves together. But as long as all the internal boundaries are eventually stitched, in no particular order, the final larger patch will be created.

The right side of Figure 86 show that same patch, but with a different knot line flow. This is done by simply moving the shape points of the now internal shape curves. The "sub-patches" refit to the polymesh, and the larger stitched patch inherits the new shape.

Figure 88. Stitching on a Face

Figure 88 shows an example of multiple patches fitted to a face (left side), and the final stitched single patch (right side).

Figure 89. Stitching on a Leg

Figure 89 shows another example of multiple patches fitted to a creature's leg (left side), and the final stitched single patch (right side).