Difference between revisions of "Center.posn"
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The position test commands ('''[[posn]]''', '''center.posn''', '''[[right.posn]]''', and '''[[obj.in.box]]''' are used to determine if a [[sceen object]]'s position is within a certain area. | The position test commands ('''[[posn]]''', '''center.posn''', '''[[right.posn]]''', and '''[[obj.in.box]]''' are used to determine if a [[sceen object]]'s position is within a certain area. | ||
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| − | The region to be tested is bounded by ('''X1''', '''Y1''') - ('''X2''', '''Y2'''). The test returns TRUE if the | + | The reference point for the '''center.posn''' command is the middle pixel of [[screen object]] '''oA''''s baseline (bottom row of the current [[cel]]). |
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| + | The region to be tested is bounded by ('''X1''', '''Y1''') - ('''X2''', '''Y2'''). The test returns TRUE if the reference point is >= '''X1''' AND <= '''X2''' AND >= '''Y1''' AND <= '''Y2'''. | ||
This test command can be combined with the <code>NOT</code> operator to test if an object is NOT in a specified region. | This test command can be combined with the <code>NOT</code> operator to test if an object is NOT in a specified region. | ||
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== Possible Errors == | == Possible Errors == | ||
| − | AGI expects the coordinates to be in upper-left to lower-right format. X1 '''must | + | AGI does not check that object number '''oA''' is a valid [[screen object]]. If it is not, the '''center.posn''' command will access invalid memory and the result of the test will be meaningless. |
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| + | AGI expects the coordinates to be in upper-left to lower-right format. '''X1''' ''must'' be less than or equal to '''X2''' and '''Y1''' ''must'' be less than or equal to '''Y2''', or the test will always fail. | ||
== Example == | == Example == | ||
Latest revision as of 10:22, 20 April 2019
The center.posn test command returns TRUE if the screen coordinates of the screen object's bottom center pixel is within a specified region.
Syntax
center.posn(obj oA, byt X1, byt Y1, byt X2, byt Y2)
Remarks
Test commands are only valid in an if statement.
The position test commands (posn, center.posn, right.posn, and obj.in.box are used to determine if a sceen object's position is within a certain area.
The reference point for the center.posn command is the middle pixel of screen object oA's baseline (bottom row of the current cel).
The region to be tested is bounded by (X1, Y1) - (X2, Y2). The test returns TRUE if the reference point is >= X1 AND <= X2 AND >= Y1 AND <= Y2.
This test command can be combined with the NOT operator to test if an object is NOT in a specified region.
Possible Errors
AGI does not check that object number oA is a valid screen object. If it is not, the center.posn command will access invalid memory and the result of the test will be meaningless.
AGI expects the coordinates to be in upper-left to lower-right format. X1 must be less than or equal to X2 and Y1 must be less than or equal to Y2, or the test will always fail.
Example
<syntaxhighlight lang="agi"> if(center.posn(o1, 40, 120, 60, 130))
{
print("the object's lower center pixel is in the box");
}
</syntaxhighlight>
Technical Information
| Required Interpreter Version: | Available in all AGI versions. |
| Byte-Code Value: | 17 (0x11 hex) |
