Fix #878

[BobLd]

This is in order to fix #878

Unfortunately some tests are now failing because we are now to able to assess to proper precision to use. We either can fix the test to make it pass, or we need to review the logic

 UglyToad.PdfPig.Tests.Parser.PageContentParserTests.CorrectlyWritesOperations
   Source: PageContentParserTests.cs line 34

Expected: ···"0 0 0 rg BT /F0 21.33 Tf 1 0 0 -1 0 140 T"···
Actual:     ···"0 0 0 rg BT /F0 21.32999999999999829 Tf 1"···

Leaving it here as a draft for the moment. @cremor feel free to have a look

[cremor]

Do you know how the expected value of 21.33 was produced back then? Which data type and format specifier was used? What is the exact value that is formatted, and is is read somewhere or calculated?

If we would change the F17 format specifier to F14 then this specific case would again be formatted as 21.33. Maybe even less precision is enough? How much precision does the PDF standard even support?

[BobLd]

Using F14 sounds good to me. For background:

Note: To represent real numbers, Acrobat 6 uses IEEE single-precision floating-point numbers,

[cremor]

If I read this correctly then even F5 would be enough.

[BobLd]

Yes you are right, that's the theoretical precision. I'm going for 9 (Microsoft recommends F7 for single precision.

I still have an issue with the change as the behaviour is not the same between Framework (some tests are failing) and dotnet8 (all tests are good)

[cremor]

Yeah, there seems to be a difference in number formatting between .NET Framework and .NET 8:
.NET Framework: https://dotnetfiddle.net/DyH0RY
.NET 8: https://dotnetfiddle.net/1YjwJ8

But this only affects numbers with more than 15 digits. Is this actually a problem? How big would a PDF page need to be so that this could be a real coordinate/size?

edit: I found this about the problem: https://stackoverflow.com/a/1658420/631802

Btw, the WriteDouble3 test fails (in both runtimes) if the current culture isn't using a dot as a decimal separator. You should add CultureInfo.InvariantCulture to that double.Parse call in the test.

[BobLd]

@cremor thanks for the help here, now updated with your feedback