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ScaleControl called only when needed

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Scaling is usually needed only when an application is running in SystemAware or PerMonitorV2 mode and the monitor has custom DPI settings that differ from the machine where the app was designed. In these scenarios, the Windows Forms runtime calculates the scale factor, based on custom DPI settings of the monitor, and calls ScaleControl(SizeF, BoundsSpecified) with the new scale factor. To improve performance, ScaleControl is now called only when the calculated scale factor is something other than 1.0F (that is, scaling is needed). This change can break your app if it overrides ScaleControl and performs any custom actions in the override.

Version introduced

.NET 6 servicing 6.0.101

Old behavior

In .NET 6 GA release and earlier versions, the virtual, public API ScaleControl(SizeF, BoundsSpecified) was called every time PerformAutoScale() was called on the container control of the application. That is, the method was called every time there is a layout or font change, regardless of whether scaling was needed.

New behavior

Starting in .NET 6 servicing releases, ScaleControl(SizeF, BoundsSpecified) is called only when there's a need to scale the form or control. The Windows Forms runtime calculates the scale factor based on the custom DPI settings of the monitor and the DPI settings of the monitor on which the application was designed. ScaleControl(SizeF, BoundsSpecified) is called only if the scale factor indicates that scaling is required.

Change category

This change affects source compatibility.

Reason for change

This change was made to improve performance and avoid unnecessary layouts.

Check if your code performs any custom, non-scaling actions in these overridable methods.

Affected APIs