[CairoPattern] a CairoPattern

[CairoStatus] CAIRO_STATUS_SUCCESS, or CAIRO_STATUS_PATTERN_TYPE_MISMATCH if pattern is not a linear gradient pattern.

[numeric] return value for the x coordinate of the first point, or NULL

[numeric] return value for the y coordinate of the first point, or NULL

[numeric] return value for the x coordinate of the second point, or NULL

[numeric] return value for the y coordinate of the second point, or NULL