Converts a QuadMesh into a TriMesh.

def trimesh(self):
        """
        Converts a QuadMesh into a TriMesh.
        """
        # Generate vertices
        xs = self.interface.coords(self, 0, edges=True)
        ys = self.interface.coords(self, 1, edges=True)

        if xs.ndim == 1:
            if np.all(xs[1:] < xs[:-1]):
                xs = xs[::-1]
            if np.all(ys[1:] < ys[:-1]):
                ys = ys[::-1]
            xs, ys = (np.tile(xs[:, np.newaxis], len(ys)).T,
                      np.tile(ys[:, np.newaxis], len(xs)))
        vertices = (xs.T.flatten(), ys.T.flatten())

        # Generate triangle simplexes
        shape = self.dimension_values(2, flat=False).shape
        s0 = shape[0]
        t1 = np.arange(np.product(shape))
        js = (t1//s0)
        t1s = js*(s0+1)+t1%s0
        t2s = t1s+1
        t3s = (js+1)*(s0+1)+t1%s0
        t4s = t2s
        t5s = t3s
        t6s = t3s+1
        t1 = np.concatenate([t1s, t6s])
        t2 = np.concatenate([t2s, t5s])
        t3 = np.concatenate([t3s, t4s])
        ts = (t1, t2, t3)
        for vd in self.vdims:
            zs = self.dimension_values(vd)
            ts = ts + (np.concatenate([zs, zs]),)

        # Construct TriMesh
        params = util.get_param_values(self)
        params['kdims'] = params['kdims'] + TriMesh.node_type.kdims[2:]
        nodes = TriMesh.node_type(vertices+(np.arange(len(vertices[0])),),
                                  **{k: v for k, v in params.items()
                                     if k != 'vdims'})
        return TriMesh(((ts,), nodes), **{k: v for k, v in params.items()
                                          if k != 'kdims'})