雨滴式的显示图片

本范例是以一个stdPicture物件来存图形，之後於PictureBox中以特殊效果来显示。因为我们想显示的只有一个图，所以不想多用另一个PictureBox来存原始图，而後再画到另一个PictureBox上，那只有用StdPicture 物件来取代PictureBox(存来源图)，但是BitBlt这个绘图函式需来源与目的的hDc，而StdPicture物件没有hDc，它只有一个Handle值，以本例来说，这Handle值便是图形的hBitmap值。所以我们只好使用MemoryDC的方式来做，产生一个MemoryDc後将BitMap图放於其上，之後便可以使用BitBlt来绘图了。'需求一个PictureBox( Named picture2)，一个Command按键)
Option Explicit
Private Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As Long, ByVal x As Long, ByVal y As Long, ByVal nWidth As Long,ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long,ByVal dwRop As Long) As Long
Private Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) As Long
Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long
Private Declare Function DeleteDC Lib "gdi32" (ByVal hdc As Long) As Long
Const SRCCOPY = &HCC0020
Private Picture1 As New StdPicture

Private Sub Command1_Click()
Dim i As Long
Dim j As Long
Dim height5 As Long, width5 As Long
Dim hMemDc As Long

'stdPicture物件的度量单位是Himetric所以要转换成Pixel
height5 = ScaleY(Picture1.Height, VBHimetric, vbPixels)
If height5 > Picture2.ScaleHeight Then
height5 = Picture2.ScaleHeight
End If
width5 = ScaleX(Picture1.Width, vbHimetric, vbPixels)
If width5 > Picture2.ScaleWidth Then
width5 = Picture2.ScaleWidth
End If
'Create Memory DC
hMemDc = CreateCompatibleDC(Picture2.hdc)
'将Picture1的BitMap图指定给hMemDc
Call SelectObject(hMemDc, Picture1.Handle)
For i = height5 To 1 Step -1
Call BitBlt(Picture2.hdc, 0, i, width5, 1, hMemDc, 0, i, SRCCOPY)
For j = i - 1 To 1 Step -1
Call BitBlt(Picture2.hdc, 0, j, width5, 1, hMemDc, 0, i, SRCCOPY)
Next j
Next
Call DeleteDC(hMemDc)
End Sub

Private Sub Form_Load()
Dim i As Long
Picture2.ScaleMode = 3 '设定成Pixel的度量单位
'设定待Display的图
Set Picture1 = LoadPicture("c:\Windows\素还真.bmp")
' ^^^^^^^^^^^^^^^^^^^^^^
' Load the picture we want to show
End Sub

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