ccontext:SetSource(source)
source. This pattern
will then be used for any subsequent drawing operation until a new
source pattern is set.
Note: The pattern's transformation matrix will be locked to the
user space in effect at the time of ccontext:SetSource(). This means
that further modifications of the current transformation matrix
will not affect the source pattern. See cpattern:SetMatrix().
The default source pattern is a solid pattern that is opaque black, that is, it is equivalent to ccontext:SetSourceRGB() with the arguments all set to 0.0.