cairoPatternAddColorStopRgb or
cairoPatternAddColorStopRgba.cairoPatternCreateRadial(cx0, cy0, radius0, cx1, cy1, radius1)cx0cy0radius0cx1cy1radius1CairoPattern] the newly created CairoPattern if successful, or
an error pattern in case of no memory.This function will always return a valid pointer, but if an error
occurred the pattern status will be set to an error. To inspect
the status of a pattern use cairoPatternStatus.
cairoPatternSetMatrix.