public override Surface CreateSurface(InterpretationContext context, Parameter xParam, Parameter yParam,
ExplanationPart explain)
{
Surface retVal = base.CreateSurface(context, xParam, yParam, explain);
Surface leftSurface = Left.CreateSurface(context, xParam, yParam, explain);
if (leftSurface != null)
{
Surface rightSurface = Right.CreateSurface(context, xParam, yParam, explain);
if (rightSurface != null)
{
retVal = CombineSurface(leftSurface, rightSurface);
}
}
retVal.XParameter = xParam;
retVal.YParameter = yParam;
return retVal;
}