I am currently creating a WPF Window which preserves its aspect ratio when resized.
My first idea was to handle the WM_SIZE Message and set the Size there, but this produced annoying flickering. So I tried to change the lParam of WM_Size which produced AccessViolationExceptions. Same happend with manipulating lParam on WM_SIZING.
AspectWindow.vb
Imports System.Runtime.InteropServices
Imports System.Windows.Interop
Public Class AspectWindow
Inherits Window
Private AspectRatio As Double
Private ResizeDirection As Direction
Enum Direction
Horizontal
Vertical
End Enum
Enum WM
WM_SIZE = &H5
WM_SIZING = &H214
WM_EXITSIZEMOVE = &H232
WM_NCCALCSIZE = &H83
End Enum
Enum WMSZ
WMSZ_BOTTOM = &H6
WMSZ_BOTTOMLEFT = &H7
WMSZ_BOTTOMRIGHT = &H8
WMSZ_LEFT = &H1
WMSZ_RIGHT = &H2
WMSZ_TOP = &H3
WMSZ_TOPLEFT = &H4
WMSZ_TOPRIGHT = &H5
End Enum
Enum WVR
WVR_VALIDRECTS = &H400
End Enum
Enum IntPtrBool
[True] = 1
[False] = 0
End Enum
<StructLayout(LayoutKind.Sequential)>
Friend Structure RECT
Public left As Long
Public top As Long
Public right As Long
Public bottom As Long
End Structure
Protected Overrides Sub OnSourceInitialized(e As EventArgs)
AspectRatio = Me.ActualWidth / Me.ActualHeight
MyBase.OnSourceInitialized(e)
Dim source As HwndSource = TryCast(HwndSource.FromVisual(Me), HwndSource)
If source IsNot Nothing Then
source.AddHook(New HwndSourceHook(AddressOf WinProc))
End If
End Sub
Private Function WinProc(hwnd As IntPtr, msg As Integer, wParam As IntPtr, lParam As IntPtr, ByRef handled As Boolean) As IntPtr
Select Case msg
Case WM.WM_SIZING
Select Case wParam
Case WMSZ.WMSZ_BOTTOM, WMSZ.WMSZ_TOP
ResizeDirection = Direction.Vertical
Exit Select
Case WMSZ.WMSZ_LEFT, WMSZ.WMSZ_RIGHT
ResizeDirection = Direction.Horizontal
Exit Select
End Select
If Not lParam = Nothing Then
Dim Rect As RECT = Marshal.PtrToStructure(Of RECT)(lParam)
If ResizeDirection = Direction.Horizontal Then
Rect.bottom = Rect.top
Else
Rect.right = Rect.top
End If
'Manipulating Resize Rectangle
Rect.top = 1
Rect.bottom = 2
Rect.left = 3
Rect.right = 4
Marshal.StructureToPtr(Of RECT)(Rect, lParam, False)
End If
Return IntPtrBool.True
End Select
Return IntPtr.Zero
End Function
End Class
Solved it with handling WM_WINDOWPOSCHANGING:
Imports System.Runtime.InteropServices
Imports System.Windows.Interop
Public Class AspectWindow
Inherits Window
Private AspectRatio As Double
Private ResizeDirection As WMSZ
Enum WM
WM_SIZING = &H214
WM_WINDOWPOSCHANGING = &H46
End Enum
Enum WMSZ
WMSZ_BOTTOM = &H6
WMSZ_BOTTOMLEFT = &H7
WMSZ_BOTTOMRIGHT = &H8
WMSZ_LEFT = &H1
WMSZ_RIGHT = &H2
WMSZ_TOP = &H3
WMSZ_TOPLEFT = &H4
WMSZ_TOPRIGHT = &H5
End Enum
Enum IntPtrBool
[True] = 1
[False] = 0
End Enum
<StructLayout(LayoutKind.Sequential)>
Friend Structure WINDOWPOS
Public hwnd As IntPtr
Public hwndInsertAfter As IntPtr
Public x As Integer
Public y As Integer
Public cx As Integer
Public cy As Integer
Public flags As Integer
End Structure
Protected Overrides Sub OnSourceInitialized(e As EventArgs)
AspectRatio = Me.ActualWidth / Me.ActualHeight
MyBase.OnSourceInitialized(e)
Dim source As HwndSource = TryCast(HwndSource.FromVisual(Me), HwndSource)
If source IsNot Nothing Then
source.AddHook(New HwndSourceHook(AddressOf WinProc))
End If
End Sub
Private Function WinProc(hwnd As IntPtr, msg As Integer, wParam As IntPtr, lParam As IntPtr, ByRef handled As Boolean) As IntPtr
Select Case msg
Case WM.WM_SIZING
ResizeDirection = wParam
Return IntPtrBool.True
Case WM.WM_WINDOWPOSCHANGING
Dim Pos = Marshal.PtrToStructure(Of WINDOWPOS)(lParam)
Dim Last = Pos
If Not ResizeDirection = WMSZ.WMSZ_TOP AndAlso Not ResizeDirection = WMSZ.WMSZ_BOTTOM Then
Pos.cy = Pos.cx / AspectRatio
End If
If Not ResizeDirection = WMSZ.WMSZ_RIGHT AndAlso Not ResizeDirection = WMSZ.WMSZ_LEFT Then
Pos.cx = Pos.cy * AspectRatio
End If
If ResizeDirection = WMSZ.WMSZ_TOPRIGHT OrElse ResizeDirection = WMSZ.WMSZ_TOPLEFT Then
Pos.y += Last.cy - Pos.cy
End If
Marshal.StructureToPtr(Of WINDOWPOS)(Pos, lParam, True)
End Select
End Function
End Class