From QB64 Wiki
The _MOUSEWHEEL function returns a positive or negative INTEGER value indicating mouse scroll clicks since the last read.
- scroll% = _MOUSEWHEEL
- A return value of 1 represent one "click" the mouse scroll wheel was moved toward the user.
- A return value of -1 represent one "click" the mouse scroll wheel was moved away from the user.
- After a "click" has been read, the value resets to 0 automatically so cumulative position values must be added.
- If no movement on the wheel has occurred since the last _MOUSEINPUT read, _MOUSEWHEEL returns 0.
Example 1: Reading the cumulative mouse wheel "clicks".
Example 2: A simple text scrolling routine using the mouse wheel value to read a text array.
DIM Array$(100) LINE INPUT "Enter a file name with 100 or more lines of text: ", file$ OPEN file$ FOR INPUT AS #1 DO UNTIL EOF(1) inputcount = inputcount + 1 LINE INPUT #1, Array$(inputcount) IF inputcount = 100 THEN EXIT DO LOOP FOR n = 1 TO 21: PRINT Array$(n): NEXT CLOSE #1 DO DO WHILE _MOUSEINPUT IF row >= 0 THEN row = row + _MOUSEWHEEL ELSE row = 0 'prevent under scrolling IF row > inputcount - 20 THEN row = inputcount - 20 'prevent over scrolling IF prevrow <> row THEN 'look for a change in row value IF row > 0 AND row <= inputcount - 20 THEN CLS: LOCATE 2, 1 FOR n = row TO row + 20 PRINT Array$(n) NEXT END IF END IF prevrow = row 'store previous row value LOOP LOOP UNTIL INKEY$ > ""