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68 lines
2 KiB
Markdown
68 lines
2 KiB
Markdown
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The [_MOUSEWHEEL](_MOUSEWHEEL) function returns a positive or negative [INTEGER](INTEGER) value indicating mouse scroll events since the last read of [_MOUSEINPUT](_MOUSEINPUT).
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## Syntax
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> scrollAmount% = [_MOUSEWHEEL](_MOUSEWHEEL)
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## Description
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* Returns -1 when scrolling up and 1 when scrolling down with 0 indicating no movement since last read.
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* After an event has been read, the value resets to 0 automatically so cumulative position values must be added.
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* If no movement on the wheel has occurred since the last [_MOUSEINPUT](_MOUSEINPUT) read, [_MOUSEWHEEL](_MOUSEWHEEL) returns 0.
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## Example(s)
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Reading the cumulative mouse wheel "clicks".
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```vb
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DO: _LIMIT 100
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DO WHILE _MOUSEINPUT
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Scroll = Scroll + _MOUSEWHEEL
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LOCATE 10, 20: PRINT Scroll
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LOOP
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LOOP UNTIL INKEY$ = CHR$(13) ' press Enter to quit
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```
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A simple text scrolling routine using the mouse wheel value to read a text array.
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```vb
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DIM Array$(100)
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LINE INPUT "Enter a file name with 100 or more lines of text: ", file$
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OPEN file$ FOR INPUT AS #1
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DO UNTIL EOF(1)
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inputcount = inputcount + 1
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LINE INPUT #1, Array$(inputcount)
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IF inputcount = 100 THEN EXIT DO
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LOOP
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FOR n = 1 TO 21: PRINT Array$(n): NEXT
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CLOSE #1
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DO
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DO WHILE _MOUSEINPUT
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IF row >= 0 THEN row = row + _MOUSEWHEEL ELSE row = 0 'prevent under scrolling
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IF row > inputcount - 20 THEN row = inputcount - 20 'prevent over scrolling
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IF prevrow <> row THEN 'look for a change in row value
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IF row > 0 AND row <= inputcount - 20 THEN
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CLS: LOCATE 2, 1
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FOR n = row TO row + 20
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PRINT Array$(n)
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NEXT
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END IF
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END IF
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prevrow = row 'store previous row value
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LOOP
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LOOP UNTIL INKEY$ > ""
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```
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Note: You will need a text file that is large enough for this example.
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## See Also
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* [_MOUSEX](_MOUSEX), [_MOUSEY](_MOUSEY), [_MOUSEBUTTON](_MOUSEBUTTON)
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* [_MOUSEINPUT](_MOUSEINPUT), [_MOUSEMOVE](_MOUSEMOVE)
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* [_MOUSESHOW](_MOUSESHOW), [_MOUSEHIDE](_MOUSEHIDE)
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* [Controller Devices](Controller-Devices)
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