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The center.posn test command returns TRUE if the screen coordinates of the screen object's bottom center pixel is within a specified region.


center.posn(obj oA, byt X1, byt Y1, byt X2, byt Y2)


Test commands are only valid in an if statement.

The position test commands (posn, center.posn, right.posn, and 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.


if(center.posn(o1, 40, 120, 60, 130)) 
  print("the object's lower center pixel is in the box");

Technical Information

Required Interpreter Version: Available in all AGI versions.
Byte-Code Value: 17 (0x11 hex)

See Also

Test Commands