打印窗口/复制从屏幕获取选定区域

Question

嘿，我这里有这段代码：

Dim p As Process = Process.GetProcessesByName("Cal").FirstOrDefault
Dim target_hwnd As Long = FindWindow(vbNullString, "Calculator")
If p IsNot Nothing Then
    SetWindowPos(target_hwnd, 0, winSize(0), winSize(1), winSize(2), winSize(3), 0)
    AppActivate(p.Id)
    Dim img As New Bitmap(145, 145) 'size fo the caption area
    Dim gr As Graphics = Graphics.FromImage(img)
    'sets the offsets and use image size to set region
    gr.CopyFromScreen(New Point(winSize(0) + 44, winSize(1) + 179), Point.Empty, img.Size)
    img.Save("test.jpg", Drawing.Imaging.ImageFormat.Jpeg)
    Process.Start("test.jpg")
End If

只要我有窗口，它就可以很好地拍摄屏幕截图，没有任何问题。但是，当我将表单移出屏幕（我看不到它）时，它只会捕获黑色图像。

我一直在尝试这段代码：

Private Declare Function PrintWindow Lib "user32.dll" (ByVal hwnd As IntPtr, ByVal hdcBlt As IntPtr, ByVal nFlags As UInt32) As Boolean
Dim screenCapture As Bitmap
Dim otherForm As New Form
Private Sub CaptureScreen()
    Dim target_hwnd As Long = FindWindow(vbNullString, "Calculator")
    SetWindowPos(target_hwnd, 0, winSize(0), winSize(1), winSize(2), winSize(3), 0)
    screenCapture = New Bitmap(245, 245)
    Dim g As Graphics = Graphics.FromImage(screenCapture)
    Dim hdc As IntPtr = g.GetHdc
    Form1.PrintWindow(target_hwnd, hdc, Nothing)
    g.ReleaseHdc(hdc)
    g.Flush()
    g.Dispose()
    If IO.File.Exists("d:test.jpg") Then
        IO.File.Delete("d:test.jpg")
    End If
    screenCapture.Save("d:test.jpg", Drawing.Imaging.ImageFormat.Jpeg)
End Sub
Private Sub Button3_Click(sender As System.Object, e As System.EventArgs) Handles Button3.Click
    CaptureScreen()
End Sub

现在，即使窗口不在屏幕外，上面的代码也会捕获图像。上面代码的问题在于，我不能告诉它只捕获该窗口中的一个区域，而我能够使用我第一次发布的CopyFromScreen来完成。

使用PrintWindow可以这样做吗？

Answer 1

我能够做到这一点：

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim fileName = "Calculator.jpg"
    Dim fileNameCrop = "Calculator-crop.jpg"
    '     |--b|---|x|
    '     |   |     |            a|-Form Left to image area
    '     |   V     |             |  b|-Form Top to image area
    '     a-->[c]   |             |   |   c|-Image area Width to capture
    '     |         |             |   |    |  c|-Image area Height to capture
    '     |_________|             V   V    V   V     
    Dim CropRect As New Rectangle(97, 189, 36, 29)
    Dim OrignalImage = Image.FromFile(fileName)
    Dim CropImage = New Bitmap(CropRect.Width, CropRect.Height)
    Using grp = Graphics.FromImage(CropImage)
        grp.InterpolationMode = Drawing2D.InterpolationMode.NearestNeighbor
        grp.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias
        grp.DrawImage(OrignalImage, New Rectangle(0, 0, CropRect.Width, CropRect.Height), CropRect, GraphicsUnit.Pixel)
        CropImage.Save(fileNameCrop)
    End Using
    OrignalImage.Dispose()
    CropImage.Dispose()
    'delete org image
    If FileIO.FileSystem.FileExists(fileName) Then FileIO.FileSystem.DeleteFile(fileName)
End Sub

在我保存了OP中发布的第一个代码中的表单图像后，只需裁剪该区域即可。