This variable array returns the alpha (transparency) value of
any one of the 8 backgrounds (numbered form 0 - 7 within the array)
of the current room. This value can be anywhere between 0 and 1,
where 0 indicates that the background is completely transparent and
1 (the default value) indicates that the background is completely
if background_alpha <1 background_alpha = 1;
The above code checks the alpha value for background0 and if it is less than 1, it sets it to 1.