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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Shrinking Icons Down to Size
Abstract
You can use the Windows application programming interface (API)
BitBlt function to modify the size of an icon. This article explains
how to enlarge or shrink an icon.
Modifying an Icon's Size
You can use the Windows application programming interface (API)
BitBlt function to create an icon that is smaller or larger than the
original icon. The BitBlt function copies a memory device context to
another memory device context. (A memory device context is a block of
memory that represents a display surface, such as an Image or Picture
Box control. See Tip 31: "Creating the Windows Wallpaper Effect for a
complete explanation of the BitBlt function.)
In the example program below, we first load an icon into an Image
control. Then we modify the Image control's Height and Width
properties so the icon becomes 75 percent smaller than its original
size. The BitBlt function is then used to copy the icon stored in the
Image control to the Picture Box control.
Example Program
1. Create a new project in Visual Basic. Form1 is created by default.
2. Add the following Constant and Declare statements to the General
Declarations section of Form1 (note that the Declare statement
must be typed as a single line of code):
Private Declare Function BitBlt Lib "GDI" (ByVal hDestDC As Integer,
ByVal X As Integer, ByVal Y As Integer, ByVal nWidth As Integer,
ByVal nHeight As Integer, ByVal hSrcDC As Integer,
ByVal XSrc As Integer, ByVal YSrc As Integer,
ByVal dwRop As Long) As Integer
Const SRCCOPY = &HCC0020
3. Add a Command Button control to Form1. Command1 is created by
default. Set its Caption property to "Shrink Icon".
4. Add the following code to the Click event for Command1:
Private Sub Command1_Click()
Dim X As Integer
Dim Y As Integer
Dim W As Integer
Dim H As Integer
Dim Ret As Integer
Image1 = LoadPicture("c:\vb\icons\misc\binoculr.ico")
Image1.Width = 0.75 * Image1.Width
Image1.Height = 0.75 * Image1.Height
Picture1.Width = Image1.Width
Picture1.Height = Image1.Height
X = Image1.Left / Screen.TwipsPerPixelX
Y = Image1.Top / Screen.TwipsPerPixelY
W = Picture1.Width / Screen.TwipsPerPixelX
H = Picture1.Height / Screen.TwipsPerPixelY
Ret = BitBlt(Picture1.hDC, 0, 0, W, H, Form1.hDC, X, Y, SRCCOPY)
Picture1.Refresh
End Sub
5. Add an Image control to Form1. Image1 is created by default. Set
its Stretch property to True.
6. Add a Picture Box control to Form1. Picture1 is created by
default. Set its AutoRedraw property to True.
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获得位图文件的信息
在Form中添加一个Picture控件和一个CommandButton控件,在Picture控件中加入一个位图文件,将下面代码加入其中:
Private Declare Function GetObject Lib "gdi32" Alias "GetObjectA" _
(ByVal hObject As Long, ByVal nCount As Long, lpObject As Any) _
As Long
Private Declare Function GetBitmapBits Lib "gdi32" (ByVal hBitmap As Long, _
ByVal dwCount As Long, lpBits As Any) As Long
Private Type BITMAP
bmType As Long
bmWidth As Long
bmHeight As Long
bmWidthBytes As Long
bmPlanes As Integer
bmBitsPixel As Integer
bmBits As Long
End Type
Private Sub Command1_Click()
Dim hBitmap As Long
Dim res As Long
Dim bmp As BITMAP
Dim byteAry() As Byte
Dim totbyte As Long, i As Long
hBitmap = Picture1.Picture.Handle
res = GetObject(hBitmap, Len(bmp), bmp) '取得BITMAP的结构
totbyte = bmp.bmWidthBytes * bmp.bmHeight '总共要多少BYTE来存图
ReDim byteAry(totbyte - 1)
'将Picture1中的图信息存到ByteAry
res = GetBitmapBits(hBitmap, totbyte, byteAry(0))
Debug.Print "Total Bytes Copied :"; res
Debug.Print "bmp.bmBits "; bmp.bmBits
Debug.Print "bmp.bmBitsPixel "; bmp.bmBitsPixel '每相素位数
Debug.Print "bmp.bmHeight "; bmp.bmHeight '以相素计算图象高度
Debug.Print "bmp.bmPlanes "; bmp.bmPlanes
Debug.Print "bmp.bmType "; bmp.bmType
Debug.Print "bmp.bmWidth "; bmp.bmWidth '以相素计算图形宽度
Debug.Print "bmp.bmWidthBytes "; bmp.bmWidthBytes '以字节计算的每扫描线长度
End Sub
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放置“透明”的图片
在 VB 中，如果你试着把一只有鸟的图片放到背景的一棵树上，你就会发现树会被鸟遮住一个矩形的区域（即鸟的图片矩形）。我们可以通过以下方法使图片上非鸟的其它部分变透明：
我们可以利用一个 WinAPI 函数 BitBlt 对图形进行一系列的位操作来达到此目的。
函数声明：
Declare Function BitBlt Lib "gdi32" Alias "BitBlt" (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
参数解释：
目标环境：hDestDC——目标设备环境；x——左上角；y——顶端；nWidth——宽；nHeight——高
源环境：hSrcDC——源设备环境；xSrc——源左上角；ySrc——源顶端；
dwRop——位处理操作，如 vbSrcAnd；vbSrcAnd；vbSrcCopy；vbSrcErase；vbSrcInvert 等
（目标环境或源环境只能是 Picture, Form 或 Printer 对象。各单位为象素。）
进行处理之前，我们需要对鸟的图片进行处理：先复制一份相同的图形，将其应该透明之处（鸟的背景）设置为黑色（设此图为sPic），再将另一图做以下处理：要复制的地方（鸟）设置为黑色，其余地方设置（鸟的背景）为白色（设此图为Mask）。
设树的图形为名dPic。
最后，请加入以下代码：
R=BitBlt(dPic.hdc,0,0,sPic.Width,sPic.Height,Mask.hdc,0,0,vbScrCopy)
R=BitBlt(dPic.hdc,0,0,sPic.Width,sPic.Height,sPic.hdc,0,0,vbScrInvert)
后记：
1、VB 中的 PaintPicture 方法提供类似功能，但速度不及此方法；
2、在此方法上稍微加入一些代码，就不难实现动画的显示。
3、VB 例子中的 CallDlls 就使用此方法。
