C ＃ WPF realizes the real-time screen capture function of screen capture box

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Preface

stay 《C# wpf Use DockPanel Implement screenshot box 》 We implemented a screenshot box , Next, we need to realize the corresponding screen capture function . Get the screenshot area and use GDI+ screenshots , Here are some details to deal with , For example, hide the controls on the screenshot box to avoid occlusion , Deal with differences dpi The position of the coordinates under the .

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One 、 Implementation steps

1、 Get the screenshot area

With 《C# wpf Use DockPanel Implement screenshot box 》 The interface of ,clipRect Is the screenshot area control object , The following two lines of code can get the exact screenshot area , And do not suffer dpi influence .

var leftTop = clipRect.PointToScreen(new Point(0, 0));
var rightBottom = clipRect.PointToScreen(new Point(clipRect.ActualWidth, clipRect.ActualHeight));

2、 Hide controls

We need hidden controls in the screenshot box , such as 8 Drag points or toolbars .

 clipRect.Visibility = Visibility.Hidden;

（1） problem

It is invalid to directly hide the control and then take a screenshot . because wpf The rendering mechanism of is completely asynchronous , It is impossible to know the exact time when the drawing on the screen is completed . therefore The screenshot immediately after hiding will still capture the control .

（2） resolvent

The simple solution is to delay screenshots , After hiding the control 500 Screen capture in milliseconds . But this method is not stable , Especially in the production environment , Users' machines are various , As long as there is a little card, it will still come out bug.
The perfect solution is to use animation , We use the multi frame rendering feature of animation and the completion of event callback to obtain the time after the control is truly painted . The specific steps are as follows ：

 Hide controls -> Create animation -> register Completed event -> Start animation ->Completed Screenshot of the event 

3、 screenshots

Use the screenshot area obtained in the above steps , combination 《C# wpf Use GDI+ Achieve screen capture 》 The simple screenshot in is completed . Restore the hidden control after screenshot .

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Two 、 Complete code

https://download.csdn.net/download/u013113678/85855030

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3、 ... and 、 Results the preview

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summary

That's what we're going to talk about today , This article briefly introduces wpf Screenshot box screenshot method . Two details need to be noted , One is dpi Handle , One is control hiding .gdi+ Screenshots are relatively easy to achieve , Of course, the implementation of the screenshot box is still slightly difficult . Such a set of screen capture functions can be used for formal projects by simply expanding the functions .