BitmapImage doesn't use logical pixels when decoding a stream

[FrayxRulez]

Describe the bug

Currently, setting DecodePixelType = DecodePixelType.Logical doesn't seem to make any difference in a WinUI 3 desktop application.

Steps to reproduce the bug

1. Set the monitor display to a scaling that's not 100%.
2. Create a new BitmapImage, specifying DecodePixelWidth and DecodePixelHeight.
3. DecodePixelType = DecodePixelType.Logical.
4. Display the bitmap in the UI.
5. Notice the blur.

Expected behavior

BitmapImage will scale decode pixel width and height accordingly to the monitor scaling when pixel type is set to logical.

Screenshots

Here's a comparison between UWP on the left and WinUI 3 on the right:

NuGet package version

WinUI 3 - Windows App SDK 0.8: 0.8.0 (If you're seeing your issue in older previews of WinUI 3, please try this release)

Windows app type

• UWP
• Win32

Device form factor

Desktop

Windows version

Insider Build (xxxxx)

Additional context

No response

[DL444]

Still experiencing this problem in Windows App SDK v1.1.2.

Also note that DisplayInformation APIs are currently not available in Windows App SDK since they require a CoreWindow. See microsoft/WindowsAppSDK#1609.

I eventually resorted to calling Win32 APIs directly to get the scaling factor and multiply it with the desired logical pixel size to get the corresponding physical pixel size, and then assign that to DecodePixelWidth. I'll post my code here for reference.

using System;
using System.Runtime.InteropServices;
using WinRT.Interop;

public static double GetWindowScaleFactor(Window window)
{
    IntPtr hwnd = WindowNative.GetWindowHandle(window);
    IntPtr hMon = MonitorFromWindow(hwnd, 1);
    int hresult = GetScaleFactorForMonitor(hMon, out int scale);
    return hresult == 0 ? scale / 100.0 : 0;
}

[DllImport("User32.dll")]
private static extern IntPtr MonitorFromWindow(IntPtr hwnd, uint dwFlags);

[DllImport("Shcore.dll")]
private static extern int GetScaleFactorForMonitor(IntPtr hMon, out int pScale);

[Marv51]

This issue is still present in WinAppSDK 1.2.2.

DecodePixelType.Logical is basically just ignored.

This results in DecodePixelWidth/Height being very inconvenient to use. As it can only be set in code and calculations with current DPI are needed.

Seems like this was deactivated during the transition to 3.0 and not fixed afterwards?

I wonder if this is tracked internally? I wonder who would know, maybe @codendone?

[DominicMaas]

I've hit this as well. Giving it a bump.

[bpulliam]

This issue should be fixed in WinAppSDK 1.3.

[JJBrychell]

It looks like the fix may not have made it into 1.3, but it is in1.4.