The '''_MOUSEWHEEL''' function returns a positive or negative [[INTEGER]] value indicating mouse scroll clicks since the last read.


{{PageSyntax}}
:::{{Parameter|scroll%}} = {{KW|_MOUSEWHEEL}}


''Usage:''
* 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".
{{CodeStart}} '' ''
 DO: {{Cl|_LIMIT}} 100
    DO WHILE {{Cl|_MOUSEINPUT}}
      Scroll = Scroll + {{Cl|_MOUSEWHEEL}}
      LOCATE 10, 20: PRINT Scroll
    LOOP
 LOOP UNTIL INKEY$ = CHR$(13) ' press Enter to quit '' ''
{{CodeEnd}}


''Example 2:'' A simple text scrolling routine using the mouse wheel value to read a text array.
{{CodeStart}} '' ''
{{Cl|DIM}} Array$(100)
{{Cl|LINE INPUT}} "Enter a file name with 100 or more lines of text: ", file$
{{Cl|OPEN}} file$ {{Cl|FOR (file statement)|FOR}} {{Cl|INPUT (file mode)|INPUT}} {{Cl|AS}} #1
{{Cl|DO...LOOP|DO}} {{Cl|UNTIL}} {{Cl|EOF}}(1)
  inputcount = inputcount + 1
  {{Cl|LINE INPUT (file statement)|LINE INPUT}} #1, Array$(inputcount)
  {{Cl|IF...THEN|IF}} inputcount = 100 {{Cl|THEN}} {{Cl|EXIT DO}}
{{Cl|LOOP}}
{{Cl|FOR...NEXT|FOR}} n = 1 {{Cl|TO}} 21: {{Cl|PRINT}} Array$(n): {{Cl|NEXT}}
{{Cl|CLOSE}} #1
DO
  {{Cl|DO...LOOP|DO}} {{Cl|WHILE}} {{Cl|_MOUSEINPUT}}
    {{Cl|IF...THEN|IF}} row >= 0 {{Cl|THEN}} row = row + {{Cl|_MOUSEWHEEL}} {{Cl|ELSE}} row = 0  'prevent under scrolling
    {{Cl|IF...THEN|IF}} row > inputcount - 20 {{Cl|THEN}} row = inputcount - 20    'prevent over scrolling
    {{Cl|IF...THEN|IF}} prevrow <> row {{Cl|THEN}} 'look for a change in row value
      {{Cl|IF...THEN|IF}} row > 0 {{Cl|AND (boolean)|AND}} row <= inputcount - 20 {{Cl|THEN}}
        {{Cl|CLS}}: {{Cl|LOCATE}} 2, 1
        {{Cl|FOR...NEXT|FOR}} n = row {{Cl|TO}} row + 20
          {{Cl|PRINT}} Array$(n)
        {{Cl|NEXT}}
      {{Cl|END IF}}
    {{Cl|END IF}}
    prevrow = row 'store previous row value
  {{Cl|LOOP}}
{{Cl|LOOP}} {{Cl|UNTIL}} {{Cl|INKEY$}} > "" '' ''
{{CodeEnd}}
{{small|Code by Ted Weissgerber}}
<center>Note: QB64 comes with a text file called ''readme.txt'' that is large enough for this example.</center>


{{PageSeeAlso}}
* [[_MOUSEX]], [[_MOUSEY]], [[_MOUSEBUTTON]]
* [[_MOUSEINPUT]], [[_MOUSEMOVE]] 
* [[_MOUSESHOW]], [[_MOUSEHIDE]]
* [[Controller_Devices]]


{{PageNavigation}}