Fix Android arrange coordinate conversion

[albyrock87]

Description of Change

Android emulator (for instance) has 2.625 display density multiplier.

Let's say you're arranging a label to this frame:

X = 112.00000000000001dp
Y = 318.66666666666669dp
Width = 187.42857142857142dp
Height = 22.095238095238095dp

If we convert this to pixels (Ceiling is how MAUI rounds it) we get

X = 294.00000000000006 => 295px
Y = 836.5 => 837px
Width = 491.99999999999994 => 492px
Height = 58px

Now here's the deal: the output rectangle must have width = 492px.

Problem is: when arranging, MAUI is converting left, right, top, bottom coordinates separately, where right = X + Width (same for bottom).

So basically we get

X + Width = (187.42857142857142 + 112.00000000000001) * 2.625

which is

299.42857142857144 * 2.625 = 786

Now if we do 786px - 295px we get 491px which is less than 492px expected platform width.
This is the reason the Label is being cut-off.

The reason MAUI is Ceiling when converting to pixel is exactly to avoid cutting content, but that's a valid reasoning only when talking about width or height.
The coordinate system should instead follow the Rounding principle to accomodate the content to the nearest pixel: in the example above, it makes no sense to convert 294.00000000000006 to 295.

This PR applies this reasoning to the arrange system.

Issues Fixed

Fixes #17884

[veikkoeeva]

@albyrock87 Just a random person here, but that looks like a solid explanation to add also in the code so it's easily discoverable also later to whoever reads the code.

[dotnet-policy-service]

Hey there @albyrock87! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[albyrock87]

I've added the comments in the code.

That said, I'm afraid this PR will generate UITests failures everywhere and it'll take forever to capture all the screenshots.

[albyrock87]

We have another option to not break all the UI tests: keep the Ceiling rounding for coordinates too, and change this behavior only with .NET10.

[rmarinho]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[rmarinho]

In theory it should generated the needed screenshots and we can just replace, or we can ask for help to finish that tedious work of updating the screenshots.

[PureWeen]

I've added the comments in the code.

That said, I'm afraid this PR will generate UITests failures everywhere and it'll take forever to capture all the screenshots.

once we see the screenshots that'll give us an idea of the magnitude of change. There's definitely a lot :-)
We'll see how subtle/large it is once those are uploaded

[PureWeen]

I think this change makes sense...

I'm a little curious about the initial conversion from px to dp and if we should be rounding that

Like, if a DP value is 294.0000000000001 it seems like we should just convert that to 294 when doing the PX to DP conversion

I'm also wondering if we should midpoint round the width and height also. It seems like that's how Android suggests always doing the rounding https://developer.android.com/training/multiscreen/screendensities#dips-pels

[albyrock87]

Like, if a DP value is 294.0000000000001 it seems like we should just convert that to 294 when doing the PX to DP conversion

I'm afraid that value comes from the centering algorithm (in this specific example) and not from PX to DP conversion.

Obviously the centering algorithm uses DP coming from a measure pass which is in PX, but that's a plain px / density without any kind of rounding and that seems correct to me.

I also wonder why we're going through float while converting DP double to PX int.

[jsuarezruiz]

Slightly impacts tests with Labels and custom FontFamily (around 1-2% of changes detected when checking the image).

Example:

Failing tests:

• FontFamily
• FontFamilyLoadsDynamically
• VerifyTextDecorationAppliedProperly
• Bugzilla53834Test
• ChildFlexLayoutContentShouldAppear
• SystemFontsShouldRenderCorrectly
• LabelHyperlinkUnderlineColor

Could you review and update the failing ones? Let me know if can help with something.

[jsuarezruiz]

Apart from the UITest, could be nice to include some device tests checking conversions.

[PureWeen]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[rmarinho]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).