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，而后再画到另一个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\aaa.bmp")

'' ^^^^^^^^^^^^^^^^^^^^^^

'' Load the picture we want to show

End Sub