cg-argument-checking

Arguments:

Returns a boolean value indicating whether some Common Graphics functions are currently checking the validity of their arguments whenever they are called. The setf of this function can be called to turn argument checking on or off.

Common Graphics doesn't do argument checking by default, for efficiency reasons. But you can turn it on for debugging purposes with (setf (cg-argument-checking) t), and turn it back off afterward with (setf (cg-argument-checking) nil).

Even when enabled, this facility will check arguments only in a small subset of all user CG functions. These are mostly low-level functions where invalid arguments may be especially confusing or might even corrupt the Lisp. For example, if you called (setf box-right) on a position object, that would write past the end of the shorter position foreign structure and corrupt memory there, though with this argument-checking facility turned on it would instead signal an informative error.

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Created 2019.8.20.