private void TriangulateWaterfallInWater(
Vector3 v1, Vector3 v2, Vector3 v3, Vector3 v4,
float y1, float y2, float waterY, Vector3 indices)
{
v1.y = v2.y = y1;
v3.y = v4.y = y2;
v1 = HexMetrics.Perturb(v1);
v2 = HexMetrics.Perturb(v2);
v3 = HexMetrics.Perturb(v3);
v4 = HexMetrics.Perturb(v4);
var t = (waterY - y2) / (y1 - y2);
v3 = Vector3.Lerp(v3, v1, t);
v4 = Vector3.Lerp(v4, v2, t);
Rivers.AddQuadUnperterbed(v1, v2, v3, v4);
Rivers.AddQuadUV(0f, 1f, 0.8f, 1f);
Rivers.AddQuadCellData(indices, weights1, weights2);
}