fade_cb() function

fade processing logic fade_data[channel].num -> Fade cycle, This value is related to CHANGE_RATE_MS and fade_ms time fade_data[channel].step -> Fade step, < 0 indicates decrement, otherwise increment. The actual meaning is delta. fade_data[channel].cycle -> This value is used for the actions. fade_data[channel].cur -> Current value fade_data[channel].final -> Final value fade_data[channel].min -> Minimum value Final, min, cur are used to define a set of ranges, which will allow grayscale changes in arbitrary ranges, not from 0% to 100%.