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WPF Pointer-Based Touch Stack

Scope

Edge

Version Introduced

4.7

Source Analyzer Status

NotPlanned

Change Description

This change adds the ability to enable an optional WM_POINTER based WPF touch/stylus stack. Developers that do not explicitly enable this should see no change in WPF touch/stylus behavior.

Current Known Issues With optional WM_POINTER based touch/stylus stack:

  • No support for real-time inking.

    • While inking and StylusPlugins will still work, they will be processed on the UI Thread which can lead to poor performance.

  • Behavioral changes due to changes in promotion from touch/stylus events to mouse events

    • Manipulation may behave differently
    • Drag/Drop will not show appropriate feedback for touch input
      • This does not affect stylus input
    • Drag/Drop can no longer be initiated on touch/stylus events
      • This can potentially hang the application until mouse input is detected.
        • Instead, developers should initiate drag and drop from mouse events.

  • Quirked

  • Build-time break

Recommended Action

Developers who wish to enable this stack can add/merge the following to their application's App.config file:

<configuration>
    <runtime>
        <AppContextSwitchOverrides value="Switch.System.Windows.Input.Stylus.EnablePointerSupport=true"/>
    </runtime>
</configuration>

Removing this or setting the value to false will turn this optional stack off.

Note that this stack is available only on Windows 10 Creators Update and above.

Affected APIs

Not detectable via API analysis

Category

Windows Presentation Foundation (WPF)