❶ 请教：用vb编程如何实现用鼠标滚轮扩大和缩小窗体上的图片
添加一个模块，输入以下代码：
Public Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Public Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long
Public Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Public Declare Function GetCursorPos Lib "user32" (lpPoint As POINTAPI) As Long
Public Declare Function WindowFromPoint Lib "user32" (ByVal xPoint As Long, ByVal yPoint As Long) As Long
Public Const GWL_WNDPROC = -4&
Public Const WM_MOUSEWHEEL = &H20A
Public Type POINTAPI
x As Long
y As Long
End Type
Public OldWindowProc As Long
Public ohwnd As Long
Public Function NewWindowProc(ByVal hwnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
On Error Resume Next
If Msg = WM_MOUSEWHEEL Then
Dim CurPoint As POINTAPI, hwndUnderCursor As Long
GetCursorPos CurPoint
hwndUnderCursor = WindowFromPoint(CurPoint.x, CurPoint.y)
If hwndUnderCursor = ohwnd Then
If wParam = -7864320 Then
If Form1.Picture1.Width < Form1.ScaleWidth Then Form1.Picture1.Width = Form1.Picture1.Width + 300
If Form1.Picture1.Height < Form1.ScaleHeight Then Form1.Picture1.Height = Form1.Picture1.Height + 240
ElseIf wParam = 7864320 Then
If Form1.Picture1.Width > 600 Then Form1.Picture1.Width = Form1.Picture1.Width - 300
If Form1.Picture1.Height > 480 Then Form1.Picture1.Height = Form1.Picture1.Height - 240
End If
End If
Else
NewWindowProc = CallWindowProc(OldWindowProc, hwnd, Msg, wParam, lParam)
End If
End Function
在Form1中放入一个Picture1控件，然后输入以下代码：
Private Sub Form_Load()
Picture1.AutoRedraw = True
Picture1.Picture = LoadPicture("e:\tmp\cd1.gif") '图片文件名，自己改
Picture1.Move 0, 0, 6000, 4800
ohwnd = Picture1.hwnd
OldWindowProc = GetWindowLong(Picture1.hwnd, GWL_WNDPROC)
Call SetWindowLong(Picture1.hwnd, GWL_WNDPROC, AddressOf NewWindowProc)
End Sub
Private Sub Picture1_Resize()
Picture1.PaintPicture Picture1.Picture, 0, 0, Picture1.ScaleWidth, Picture1.ScaleHeight
End Sub