[iOS, Mac] Fix for image is being flipped after downsizing

[SyedAbdulAzeemSF4852]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Issue Details

• When an image is downsized on iOS, the resulting image appears upside down and is also scaled.

Root Cause

Scaling Issue :

• The UIGraphicsImageRenderer constructor without format defaults to Scale=0 (device scale), causing the same downsizing operation to produce different pixel dimensions on different devices (1x/2x/3x scale factors), leading to inconsistent image processing results.

Flipping Issue :

• Core Graphics uses a bottom-left origin, while UIKit uses a top-left origin, so images drawn without adjusting the coordinate system appearing upside down.

Description of Change

• Included an early return to bypass scaling when the image's current size matches the target size.

Scaling Issue :

• Explicitly controlled scale factor to preserve original image characteristics.
• Setting Scale = target.CurrentScale maintains the original image's pixel density, preventing device-specific scaling from being applied.

Flipping Issue:

• Replaced CGContext's DrawImage method with UIImage's Draw method, which utilizes UIKit’s top-left coordinate system.
• This change ensures the image is rendered with the correct orientation, eliminating the need for manual flipping or coordinate adjustments.

Issues Fixed

Fixes #30350

Validated the behaviour in the following platforms

• Windows
• Android
• iOS
• Mac

Output

Before	After

[Copilot]

Pull Request Overview

This PR fixes inconsistent scaling and upside-down rendering when downsizing UIImage on iOS and Mac by explicitly setting the renderer’s scale and correcting the Core Graphics coordinate system, and adds UI tests to validate the fix.

• Explicitly set UIGraphicsImageRendererFormat.Scale to target.CurrentScale to preserve pixel density.
• Adjust Core Graphics transforms to align the origin with UIKit’s top-left.
• Added shared and host-app UI tests to verify that a downsized image renders right-side up.

Reviewed Changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated no comments.

File	Description
src/Graphics/src/Graphics/Platforms/iOS/UIImageExtensions.cs	Added renderer format with explicit scale and CTM adjustments for flipping
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue30350.cs	Introduced a shared UI test to verify the downsized image isn’t flipped
src/Controls/tests/TestCases.HostApp/Issues/Issue30350.cs	Added host app sample page and label/Image setup for the issue

Comments suppressed due to low confidence (2)

src/Controls/tests/TestCases.HostApp/Issues/Issue30350.cs:40

• Avoid using async void for InitAsync; consider returning a Task and invoking it in OnAppearing or an async lifecycle method so you can await it and catch exceptions.

	private async void InitAsync()

src/Controls/tests/TestCases.HostApp/Issues/Issue30350.cs:29

• You assign downsizedSizeLabel and downsizedSource after setting Content, but neither the Label nor Image will update automatically. Use data binding or update the UI elements on the main thread after loading completes.

				new Label

[hflexgrig]

Is there any prerelease build available for this PR? I'd like to check on my app how it behaves..

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[jsuarezruiz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[mattleibow]

I think this is a bug in iOS: #30465 (comment)

So maybe use Center and then re-enable for all platforms.

[SyedAbdulAzeemSF4852]

@mattleibow , Based on the suggestion, I replaced AspectFit with AspectCenter. However, the behavior is still inconsistent across platforms. For your reference, I’ve attached the relevant screenshots below.

Android	Windows	Mac	iOS

[mattleibow]

This is a bug in iOS I think: #30465 (comment). We should use center and just try running everywhere again.

[SyedAbdulAzeemSF4852]

@mattleibow , As suggested, I’ve used Aspect.Center and shared my analysis in this comment.

[jsuarezruiz]

@SyedAbdulAzeemSF4852 COuld you rebase and fix the conflict?

[SyedAbdulAzeemSF4852]

@SyedAbdulAzeemSF4852 COuld you rebase and fix the conflict?

@jsuarezruiz , Since the revert PR #30421 has been merged and the issue no longer reproduces with that fix, my changes are no longer necessary. Therefore, I’m closing this PR.