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  1. JDK
  2. JDK-8306990

The guarantees given by Region's floor and ceiling functions should work for larger values

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Details

    • Bug
    • Resolution: Fixed
    • P4
    • jfx21
    • jfx11, 8
    • javafx
    • None
    • b20

    Description

      Region has floor and ceiling functions that ensure that calling them twice in a row will yield the same result:

           ceil(x) = ceil(ceil(x))

      However, due to use of a constant `EPSILON` which is added/subtracted before doing the rounding, this only works for small numbers (in the range of 0-50 approximately). For larger values and scales, rounding errors can easily occur. This is visible as artifacts on screen where controls are a pixel wider than they should be.

      The use of the `EPSILON` constant is incorrect, as its value depends on the magnitude of the value in question (as magnitude increases, the fractional precision decreases).

      The Math class offers the function `ulp` that should be used here. It represents the smallest possible change in value for a given double.

      Extending the existing test case `snappingASnappedValueGivesTheSameValueTest` to use larger magnitude numbers exposes the problems.

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              jhendrikx John Hendrikx
              jhendrikx John Hendrikx
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                Updated:
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