Linux: RHI/MultiViewportSwapchainComponent background window contents get scaled down to the small window size

[LB-ArturZieba]

Describe the bug Disclaimer: This issue should not be viewed (Video section) nor reproduced by photosensitive individual (as per warning when launching RHI/MultiViewportSwapchainComponent).

As shown in https://github.com/o3de/o3de-atom-sampleviewer/wiki/RHI-Samples#multiviewportswapchaincomp, contents of the big window in the background should remain properly scaled:

Meanwhile on Linux, contents of the big window in the background get scaled down to the size of the smaller window.

This issue does not occur on Windows DX12 nor Vulkan RHIs.

Prerequisites

• O3DE engine available.
• AtomSampleViewer project built.

Steps to reproduce

1. Go to Samples > RHI > MultiViewportSwapchainComponent.
2. OK on the Photosensitive Seizure Warning has to be clicked to proceed.

Expected behavior Contents of the big window in the background keep their scale.

Actual behavior Contents of the big window in the background are adjusted to the size of the small window.

Video

https://user-images.githubusercontent.com/86952082/228854275-4ee38758-9b88-4d49-b8a9-17b1601f9079.mp4

Found in Branch O3DE Installer - Stabilization/2305 (26273c22ff71950eb68d137fed25125ebbaa12d6) AtomSampleViewer - Stabilization/2305 (cee84fa2a7e85b08128271afef3c36b06284d8d7)

Desktop

• Device: PC
• OS: Linux
• Version: Ubuntu 22.04.1 LTS
• CPU AMD Ryzen 5 3600
• GPU NVIDIA GeForce RTX 2060 SUPER
• Memory 16GB