## 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.

- [X] 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:

```xml
<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)

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# Original bug
197685
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