BGCHK is not a function in SmileBasic V1.
BGCHK is a function which takes one numerical parameter which gets rounded down: a 'layer', 0 for BG foreground layer, 1 for BG background layer (same as the first parameter of the
BGOFS command). The function will normally return
FALSE. After a
BGOFS is applied to this layer with an 'interpolation time' of 1 or more, it will return
TRUE until the interpolation time expires, but if the interpolation time is 0 or missing, it will return
FALSE. In other words, while there is a
BGOFS in effect that has not yet completed moving the layer, the result is
TRUE, and at all other times when the layer is not moving, it's
If a negative value, or a value of 2 or greater, is passed to the function, the system generates a misleading
Overflow (BGCHK) error.
No information on SmileBasic V3.