RFR: 8316518 javafx.print.Paper getWidth / getHeight rounds values, causing errors.

[John Hendrikx]

On Sat, 23 Sep 2023 05:39:12 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> what kind of FP error could option 1 lead to?
>> 
>> I think rounding belongs to the UI, to the panel which displays the sizes with precision given by the requirements.  So this method, I think, should return the unmodified value.
>> 
>> Looking at AWT Paper, I see no rounding there.  Where did it come from to FX?
>> 
>> PS. my other comments are indeed unrelated to this PR.  sorry.
>
> Some observations on the paper class:
> 
>     /**
>      * Specifies the North American legal size, 8.5 inches by 14 inches.
>      */
>     public static final Paper LEGAL = new Paper("Legal", 8.4, 14, INCH);
> 
> 
> The comment and actual size contradict each other. 8.4 inches would not result in an integer number of points (604.8) and looking up the legal paper size confirms it should be 8.5 inches
> 
>     /**
>      * Specifies the Monarch envelope size, 3.87 inch by 7.5 inch.
>      */
>     public static final Paper MONARCH_ENVELOPE = new Paper("Monarch Envelope", 3.87, 7.5, INCH);
> 
> This seems incorrect, the size is 3-7/8” x 7-1/2”, which would be `3.875` x `7.5` -- the difference in this case is small enough that it will be rounded to the same value in points.

About the rounding; all these values are fixed values and could have been entered in points as constants directly.

Also realize that all papers measured in inches can be expressed exactly in points (after the above errors are fixed) so no rounding is needed for those at all; the same is not true for the papers specified in millimeters.

Since the papers in inches never should need any rounding, the rounding can therefore be removed for those.  If there is a worry that the multiplication (* 72) may cause floating point errors, then I suggest to specify all papers in points immediately, like this:

    new Paper("Letter", 8.5 * 72, 11 * 72, POINT);

As for the papers specified in millimeters, these can't be expressed in whole points, as a millimeter is equivalent to `2,83465` points.  Rounding them to points will require some guess work to find out what the actual size in millimeters was, for example, when it says 3 points it must have been 1 mm, while 1, 2, 4 or 5 points has no direct mm equivalent.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1244#discussion_r1334928344