cairo:pattern-add-color-stop-rgba (pattern offset red green blue alpha)

pattern -- a cairo:pattern-t instance
offset -- a number for an offset in the range [0.0 .. 1.0]
red -- a number for the red component of the color
green -- a number for the green component of the color
blue -- a number for the blue component of the color
alpha -- a number for the alpha component of the color

Adds a translucent color stop to a gradient pattern. The offset specifies the location along the control vector of the gradient. For example, a linear control vector of the gradient is from (x0,y0) to (x1,y1) while a radial control vector of the gradient is from any point on the start circle to the corresponding point on the end circle. The color is specified in the same way as in the cairo:set-source-rgba function.

If two or more stops are specified with identical offset values, they will be sorted according to the order in which the stops are added, stops added earlier will compare less than stops added later. This can be useful for reliably making sharp color transitions instead of the typical blend. If the pattern argument is not a gradient pattern, for example a linear or radial pattern, then pattern will be put into an error status with a :pattern-type-mismatch status. The arguments are coerced to double floats before being passed to the foreign C function.