Image size when capturing a screenshot of another application changes if application not at 0,0

Question

I have an app which properly captures the image of an application window if it is in the upper-left corner of the primary screen.
But if it is not, the image size is not correct (the window image height becomes stretched if it is against the right margin and down from the screen top. Application at 0,0

Imports System.Data.SqlClient
Imports System.Runtime.InteropServices
Imports Microsoft.VisualBasic.Strings
Imports System
Imports System.Data
Imports System.Data.OleDb

Public Class Form1
    Public Declare Function GetWindowRect Lib "user32" (ByVal HWND As Integer, ByRef lpRect As Rectangle) As Integer
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    End Sub
    Private Sub BtnCapture_Click(sender As Object, e As EventArgs) Handles BtnCapture.Click

        Dim FoundApplication As Boolean = False
        Dim localAll As Process() = Process.GetProcesses()
        Dim rect As New Rectangle
        Dim Top As Int32 = 0
        Dim Left As Int32 = 0
        Dim width As Int32
        Dim height As Int32
        Dim hwnd As IntPtr
        Dim memoryImage As Bitmap

        For Each x As Process In localAll
            GetWindowRect(x.MainWindowHandle, rect)
            If x.ProcessName.ToString = "calc" Then

                width = rect.Width
                height = rect.Height
                Top = rect.Top
                Left = rect.Left
                hwnd = x.MainWindowHandle
                FoundApplication = True
                Exit For

            End If
        Next

        If FoundApplication Then
            ' do nothing - set above
        Else
            ' set the default to entire Primary screen if Calc not found
            width = Screen.PrimaryScreen.Bounds.Width
            height = Screen.PrimaryScreen.Bounds.Height
        End If

        Dim MyGraphics As Graphics = Graphics.FromHwnd(hwnd)
        Dim s As New Size(width, height)
        memoryImage = New Bitmap(width, height, myGraphics)
        Dim memoryGraphics As Graphics = Graphics.FromImage(memoryImage)
        memoryGraphics.CopyFromScreen(Top, Left, 0, 0, s)
        Clipboard.SetImage(memoryImage)

        RtbLog.AppendText(Today().ToShortDateString & " " & Now().ToShortTimeString & vbCrLf)
        RtbLog.Paste()
        myGraphics.Dispose()
    End Sub
End Class

This simple version exhibits the behavior I am dealing with.
If the "calc" is in the upper left corner it's perfect - move it down or to the left and the image includes other parts of the screen and may cut off the image of "calc".

Answer 1

Your code can be simplified in some details.
First of all, as already mentioned in the comments, your declaration of GetWindowRect() is not correct. You need to pass it a Window handle, usually in the form of an IntPtr structure, and a RECT structure.

Refer to the PInvoke website when you need to include a Windows API function call in your code. The experience of many programmers has forged :) those lines of code.

The Desktop size, here, is returned by SystemInformation.PrimaryMonitorSize.
You could also use Screen.PrimaryScreen.Bounds or SystemInformation.VirtualScreen.
Choose the one that best fits your plans.

Imports System.Diagnostics
Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Runtime.InteropServices

<DllImport("user32.dll")>
Private Shared Function GetWindowRect(ByVal hWnd As IntPtr, ByRef lpRect As RECT) As Boolean
End Function

<StructLayout(LayoutKind.Sequential)>
Public Structure RECT
    Public Left As Integer
    Public Top As Integer
    Public Right As Integer
    Public Bottom As Integer
End Structure

Private Sub BtnCapture_Click(sender As Object, e As EventArgs) Handles BtnCapture.Click
    Dim wRect As RECT = Nothing
    Dim WindowArea As Rectangle = Nothing

    Dim FindProcess As Process = Process.GetProcessesByName("calc").FirstOrDefault()
    If FindProcess IsNot Nothing AndAlso CInt(FindProcess.MainWindowHandle) > 0 Then
        If GetWindowRect(FindProcess.MainWindowHandle, wRect) Then
            WindowArea = Rectangle.FromLTRB(wRect.Left, wRect.Top, wRect.Right, wRect.Bottom)
        End If
    End If
    If WindowArea = Nothing Then WindowArea = New Rectangle(Point.Empty, SystemInformation.PrimaryMonitorSize)
    Using img As Image = New Bitmap(WindowArea.Width, WindowArea.Height, PixelFormat.Format32bppArgb)
        Using g As Graphics = Graphics.FromImage(img)
            g.SmoothingMode = SmoothingMode.HighQuality
            g.CopyFromScreen(WindowArea.Location, Point.Empty, WindowArea.Size, CopyPixelOperation.SourceCopy)
            img.Save("[The Image Path]", ImageFormat.Png)
            ScaleToClipboard(img, 65.0F) '65% of its original size or 
        End Using
    End Using
    '(...) Other processing
End Sub

Edit:
A method to save the original image to disk, reduce the source Image size to a specific size or to a fraction of it, then set the modified Image to the ClipBoard, ready to be pasted in some recepient.

ScaleToClipboard([Source Image], [Percent of Original] As Single)
ScaleToClipboard([Source Image], [Specific Size] As Size)

Example:
ScaleToClipboard([Source Image], 72.0F)
ScaleToClipboard([Source Image], New Size(200, 125))

Private Sub ScaleToClipboard(SourceImage As Image, SizeScale As Single)
    Dim NewSize As SizeF = New SizeF((SourceImage.Width \ 100) * SizeScale, (SourceImage.Height \ 100) * SizeScale)
    ScaleToClipboard(SourceImage, Size.Round(NewSize))
End Sub

Private Sub ScaleToClipboard(SourceImage As Image, SizeScale As Size)
    Using img As Image = New Bitmap(SourceImage, Size.Round(SizeScale))
        Using g As Graphics = Graphics.FromImage(img)
            g.SmoothingMode = SmoothingMode.HighQuality
            g.InterpolationMode = InterpolationMode.HighQualityBicubic
            g.DrawImage(SourceImage, New Rectangle(Point.Empty, SizeScale))
            Clipboard.SetImage(TryCast(img.Clone(), Image))
        End Using
    End Using
End Sub