CairoPattern corresponding to a translucent color.
The color components are floating point numbers in the range 0 to
1. If the values passed in are outside that range, they will be
clamped.cairoPatternCreateRgba(red, green, blue, alpha)redgreenbluealphaCairoPattern] 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.