Why Does My DPI-Unaware Application Suddenly Become DPI-Aware After an Update?

Unexpected DPI Awareness Changes After Application Updates

Some applications, originally designed as DPI-unaware (relying on Windows' UI scaling), may unexpectedly become DPI-aware (System Aware) following minor updates. This occurs even if the application manifest and external dependencies remain unchanged.

Root Cause:

This behavior is often caused by DPI-aware third-party components or dependencies. Even with an explicit DPI-Unaware declaration in the application manifest, inclusion of such components can override the setting, forcing DPI-awareness.

Solutions for Defining DPI Awareness:

Several approaches can explicitly control an application's DPI awareness:

1. Modifying the Application Manifest:

• Modify app.manifest to include (or uncomment) the following:

<code class="language-xml"><dpiaware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">false</dpiaware></code>

2. Utilizing Windows API Functions:

The appropriate API call depends on the Windows version:

• Windows 7:

<code class="language-csharp">[DllImport("user32.dll", SetLastError = true)]
static extern bool SetProcessDPIAware();</code>

• Windows 8.1:

<code class="language-csharp">[DllImport("shcore.dll")]
static extern int SetProcessDpiAwareness(ProcessDPIAwareness value);

enum ProcessDPIAwareness
{
    DPI_Unaware = 0,
    System_DPI_Aware = 1,
    Per_Monitor_DPI_Aware = 2
}</code>

• Windows 10 (1703 and later):

<code class="language-csharp">[DllImport("user32.dll", SetLastError = true)]
static extern int SetProcessDpiAwarenessContext(DpiAwarenessContext value);

enum DpiAwarenessContext
{
    Context_Unaware = (DPI_AWARENESS_CONTEXT)-1,
    Context_SystemAware = (DPI_AWARENESS_CONTEXT)-2,
    Context_PerMonitorAware = (DPI_AWARENESS_CONTEXT)-3,
    Context_PerMonitorAwareV2 = (DPI_AWARENESS_CONTEXT)-4
}</code>

3. Using AssemblyInfo.cs:

Add this attribute to override system-defined DPI awareness based on component references:

<code class="language-csharp">[assembly: System.Windows.Media.DisableDpiAwareness]</code>

Important Considerations:

• DPI awareness is thread-specific. Use thread-specific API functions for granular control over individual threads.
• Ensure all third-party components and dependencies are consistent with the desired DPI awareness level.

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