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80 lines
3.7 KiB
Plaintext
80 lines
3.7 KiB
Plaintext
'''VARPTR$''' is a memory function that returns a [[STRING]] representation of a variable's memory address value for use in a [[DRAW]] or [[PLAY]] statement.
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{{PageSyntax}}
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:: string_value$ = VARPTR$(''variable'')
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* Can use any [[STRING|string]] or numerical variable reference '''existing''' in memory.
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* If the parameter value is from an array it must be dimensioned already. Cannot use fixed length string arrays.
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* When using '''numerical''' ''variable'' values in [[DRAW]] strings, use an = sign after the function letter. "TA=" + VARPTR$(''variable%'')
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* Always use variable X as in "X" + VARPTR$(''string_variable$'') to [[DRAW]] or [[PLAY]] another [[STRING]] value.
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* DRAW relative Moves use a + or - before the equal sign. EX: DRAW "M+=" + VARPTR$(x%) + ",-=" + VARPTR$(y%)
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''Example 1:'' How VARPTR$ reads consecutive values from memory.
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{{CodeStart}} '' ''
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{{Cl|SCREEN (statement)|SCREEN}} 2
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{{Cl|CLS}}
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WIND$ = "r10 d7 l10 u7 br20" 'create draw string to be read by function
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ROW$ = "x"+{{Cl|VARPTR$}}(WIND$)+"x"+{{Cl|VARPTR$}}(WIND$)+"x"+{{Cl|VARPTR$}}(WIND$)+" x"+{{Cl|VARPTR$}}(WIND$)+"bl80 bd11"
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{{Cl|LINE}} (100, 50)-(200, 160), , B
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{{Cl|DRAW}} "bm 115,52"
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{{Cl|FOR...NEXT|FOR}} I = 1 {{Cl|TO}} 10
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{{Cl|DRAW}} "x" + {{Cl|VARPTR$}}(ROW$)
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{{Cl|NEXT}} '' ''
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{{CodeEnd}}
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:''NOTE:'' '''GWBasic''' allows '''semicolons''' to be used in the ROW$ definition, but Qbasic and '''QB64''' MUST use '''+''' concatenation.
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''Example 2:'' Using the function to change a Turn Angle value using DRAW.
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{{CodeStart}} '' ''
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{{Cl|SCREEN (statement)|SCREEN}} 12
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'Demonstrates how string DRAW angles are used with TA
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{{Cl|FOR...NEXT|FOR}} i = 0 {{Cl|TO}} 360 {{Cl|STEP}} 30 'mark clock hours every 30 degrees
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angle$ = {{Cl|STR$}}(i) 'change degree value i to a string
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{{Cl|PSET}} (175, 250), 6 'clock center
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{{Cl|DRAW}} "TA" + angle$ + "BU100" 'add string angle to Turn Angle and draw blind up
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{{Cl|CIRCLE}} {{Cl|STEP}}(0, 0), 5, 12 'place a circle at end of Up line
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{{Cl|DRAW}} "P9, 12"
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{{Cl|_DELAY}} .5
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{{Cl|NEXT}}
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'Demonstrates how VARPTR$ is used with TA=
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{{Cl|DO}}: sec$ = {{Cl|RIGHT$}}({{Cl|TIME$}}, 2) 'get current second value from time
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degree = {{Cl|VAL}}(sec$) * -6 'use a negative value to Turn Angle clockwise
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{{Cl|PSET}} (175, 250), 9 'clock center
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{{Cl|DRAW}} "TA=" + {{Cl|VARPTR$}}(degree) + "U90" 'VARPTR$ value requires = in DRAW
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{{Cl|DO}}: {{Cl|_LIMIT}} 30: {{Cl|LOOP}} {{Cl|UNTIL}} {{Cl|RIGHT$}}({{Cl|TIME$}}, 2) <> sec$ 'loop until seconds value changes
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{{Cl|IF}} {{Cl|INKEY$}} <> "" {{Cl|THEN}} {{Cl|EXIT DO}}
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{{Cl|PSET}} (175, 250), 0
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{{Cl|DRAW}} "TA=" + {{Cl|VARPTR$}}(degree) + "U90" 'erase previous second hand draw
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{{Cl|LOOP}} '' ''
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{{CodeEnd}}
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:''Explanation:'' When the VARPTR$ value is used in DRAW, '''=''' MUST be used to pass the value to the draw! Negative Turn Angle values move clockwise and each second moves the hand 6 degrees. '''TA''' uses actual degree angles starting at 0 or noon.
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''Example 3:'' Comparing DRAW moves using VARPTR$ and [[STR$]] values.
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{{CodeStart}} '' ''
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{{Cl|SCREEN}} 12
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{{Cl|PSET}} (200, 200), 12
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{{Cl|CIRCLE}} {{Cl|STEP}}(0, 0), 5, 10
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A = 100: B = 100
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{{Cl|DRAW}} "M+=" + {{Cl|VARPTR$}}(A) + ",-=" + {{Cl|VARPTR$}}(B)
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{{Cl|PSET}} (400, 400), 10
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{{Cl|CIRCLE}} {{Cl|STEP}}(0, 0), 5, 12
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C = 100: D = -100
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{{Cl|DRAW}} "M+" + {{Cl|STR$}}(C) + "," + {{Cl|STR$}}(D) 'must add + for positive relative moves
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{{Cl|END}} '' ''
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{{CodeEnd}}
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: ''Explanation:'' A negative STR$ value will move the DRAW relatively where VARPTR$ won't without the sign before the equal.
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''See also:''
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* [[VARPTR]], [[STR$]]
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* [[DRAW]], [[PLAY]]
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{{PageNavigation}}
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