[0.84] fix: correct CompositionHwndHost initialization order for DPI-aware second windows#16148
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…econd windows (#7) * fix: correct CompositionHwndHost initialization order for DPI-aware second windows CompositionHwndHost::Initialize() connected the ContentIsland to the DesktopChildSiteBridge before setting the ResizePolicy, causing the island's coordinate space to be configured without proper DPI awareness. This led to InputPointerSource delivering touch coordinates that did not account for the display's scale factor on secondary windows at non-100% zoom. Reorders initialization to match ReactNativeWindow::ContentSiteBridge(): ResizePolicy is now set before Connect, and ScaleFactor is set before the island is connected. Also adds WM_DPICHANGED handling to TranslateMessage so the island's scale factor and layout are updated if the display DPI changes at runtime. * Update CompositionHwndHost.cpp * Update CompositionHwndHost.cpp * host lost on function return * Update CompositionHwndHost.cpp * Create react-native-windows-c628c673-e01f-4887-9fcf-b1e5c468d311.json
gmacmaster
changed the title
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Will create port to main if this looks good |
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Do we need the WM_DPICHANGED handler? Don't we get a RasterizationScaleChange from the ContentIsland? |
acoates-ms
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May 18, 2026
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| HWND m_hwnd; | ||
| winrt::Microsoft::ReactNative::ReactNativeIsland m_compRootView{nullptr}; | ||
| winrt::Microsoft::UI::Content::DesktopChildSiteBridge m_bridge{nullptr}; |
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And now we dont need to store the DesktopChildSiteBridge...
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Description
Type of Change
Why
CompositionHwndHost::Initialize()connected theContentIslandto theDesktopChildSiteBridgebefore setting theResizePolicy, causing the island's coordinate space to be configured without proper DPI awareness. This led toInputPointerSourcedelivering touch coordinates that did not account for the display's scale factor on secondary windows at non-100% zoom.What
Initialization reorder (
CompositionHwndHost.cpp/.h):DesktopChildSiteBridgefrom a local variable to a member (m_bridge) so it survives pastInitialize().Initialize()so thatResizePolicyis set beforeConnect, andScaleFactoris set before the island is connected — matching theReactNativeWindow::ContentSiteBridgereference pattern.Runtime DPI changes (e.g., moving the window between monitors with different scales) are already handled by
ReactNativeIsland'sContentIsland::StateChangedsubscription, which responds toDidRasterizationScaleChange()and callsScaleFactor()→Arrange()directly.Screenshots
N/A — this is a behavioral/layout correctness fix; the visual result is that touch input on secondary windows at non-100% DPI now aligns correctly with their visual positions.
Testing
Verified locally by:
CompositionHwndHostwindow on a 150% DPI display — touch targets now align correctly with their visual positions.ReactNativeIsland'sRasterizationScaleChangedsubscription).Changelog
Should this change be included in the release notes: yes
Fix
CompositionHwndHostinitialization order so thatResizePolicyis set beforeConnectandScaleFactorbefore the island is connected, ensuring secondary windows render with correct DPI-aware touch coordinates.