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默认单位是像素
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96是系统的一种设定，每英寸的点数，是系统界面用小字体时的设置
用像素数除以DPI没有意义
网络上找到这个比较全面，你试一下，我记得以前也是这么设置的。
int GetDeviceCaps( HDC hdc, int nIndex);
其中，hdc用来指定设备环境句柄，nIndex用来指定要获取的参量索引，对于打印机而言，它常常需要下列的预定义值：
LOGPIXELSX 打印机水平分辨率
LOGPIXELSY 打印机垂直分辨率
PHYSICALWIDTH 打印纸的实际宽度
PHYSICALHEIGHT 打印纸的实际高度
PHYSICALOFFSETX 实际可打印区域的物理左边距
PHYSICALOFFSETY 实际可打印区域的物理上边距
下面的函数代码就是用来设置页边距，并且还计算页面的物理边距：
void CEx_Prn1View::SetPageMargin(CDC *pDC, CPrintInfo *pInfo, int l, int t, int r, int b)
// l, t, r, b分别表示左上右下边距, 单位为0.1mm
{
int nOldMode = pDC- GetMapMode();
pDC- SetMapMode(MM_LOMETRIC);
// 计算一个设备单位等于多少0.1mm
double scaleX = 254.0 / (double)GetDeviceCaps(
pDC- m_hAttribDC, LOGPIXELSX);
double scaleY = 254.0 / (double)GetDeviceCaps(
pDC- m_hAttribDC, LOGPIXELSY);
int x = GetDeviceCaps(pDC- m_hAttribDC,
PHYSICALOFFSETX);
int y = GetDeviceCaps(pDC- m_hAttribDC,
PHYSICALOFFSETY);
int w = GetDeviceCaps(pDC- m_hAttribDC,
PHYSICALWIDTH);
int h = GetDeviceCaps(pDC- m_hAttribDC,
PHYSICALHEIGHT);
int nPageWidth = (int)((double)w*scaleX + 0.5);
// 纸宽，单位0.1mm
int nPageHeight = (int)((double)h*scaleY + 0.5);
// 纸高，单位0.1mm
m_nPhyLeft = (int)((double)x*scaleX + 0.5);
// 物理左边距，单位0.1mm
m_nPhyTop = (int)((double)y*scaleY + 0.5);
// 物理上边距，单位0.1mm
pDC- DPtoLP(pInfo- m_rectDraw);
CRect rcTemp = pInfo- m_rectDraw;
rcTemp.NormalizeRect();
m_nPhyRight = nPageWidth - rcTemp.Width() -
m_nPhyLeft; // 物理右边距，单位0.1mm
m_nPhyBottom = nPageHeight - rcTemp.Height() -
m_nPhyTop; // 物理下边距，单位0.1mm
// 若边距小于物理边距，则调整它们
if (l m_nPhyLeft) l = m_nPhyLeft;
if (t m_nPhyTop) t = m_nPhyTop;
if (r m_nPhyRight) r = m_nPhyRight;
if (b m_nPhyBottom) b = m_nPhyBottom;
// 计算并调整pInfo- m_rectDraw的大小
pInfo- m_rectDraw.left = l - m_nPhyLeft;
pInfo- m_rectDraw.top = - t + m_nPhyTop;
pInfo- m_rectDraw.right -= r - m_nPhyRight;
pInfo- m_rectDraw.bottom += b - m_nPhyBottom;
pDC- LPtoDP(pInfo- m_rectDraw);
pDC- SetMapMode(nOldMode);
// 恢复原来的映射模式
}
您可以用下面给出这一小段代码检测当前屏幕分辨率，然后根据结果作出反应──例如，重新调整窗体大小以适应用程序户分辨率。
Public Function CheckRez(pixelWidth As Long, pixelHeight As Long) As Boolean
'
Dim lngTwipsX As Long
Dim lngTwipsY As Long
'
' convert pixels to twips
lngTwipsX = pixelWidth * 15
lngTwipsY = pixelHeight * 15
'
' check against current settings
If lngTwipsX Screen.Width Then
CheckRez = False
Else
If lngTwipsY Screen.Height Then
CheckRez = False
Else
CheckRez = True
End If
End If
'
End Function
Next, run the following code at the start of the program:
If CheckRez(640, 480) = False Then
MsgBox "Incorrect screen size!"
Else
MsgBox "Screen Resolution Matches!"
End If
这篇文章介绍了VB.NET设置屏幕分辨率、颜色位数、刷新率
实例代码，有需要的朋友可以参考一下
复制代码
代码如下:
Private
Declare
Function
GetDeviceCaps
Lib
"gdi32"
(ByVal
hdc
As
Long,
ByVal
nIndex
As
Long)
As
Long
Private
Declare
Function
ChangeDisplaySettings
Lib
"user32"
Alias
"ChangeDisplaySettingsA"
(lpDevMode
As
Any,
ByVal
dwflags
As
Long)
As
Long
Private
Const
CCDEVICENAME
As
Long
=
32
Private
Const
CCFORMNAME
As
Long
=
32
Private
Const
DM_BITSPERPEL
As
Long
=
H40000
Private
Const
DM_PELSWIDTH
As
Long
=
H80000
Private
Const
DM_PELSHEIGHT
As
Long
=
H100000
Private
Const
DM_DISPLAYFLAGS
As
Long
=
H200000
Private
Const
DM_DISPLAYFREQUENCY
=
H400000
Private
Const
CDS_FORCE
As
Long
=
H80000000
Private
Const
BITSPIXEL
As
Long
=
12
Private
Const
HORZRES
As
Long
=
8
Private
Const
VERTRES
As
Long
=
10
Private
Const
VREFRESH
=
116
Private
Type
DEVMODE
dmDeviceName
As
String
*
CCDEVICENAME
dmSpecVersion
As
Integer
dmDriverVersion
As
Integer
dmSize
As
Integer
dmDriverExtra
As
Integer
dmFields
As
Long
dmOrientation
As
Integer
dmPaperSize
As
Integer
dmPaperLength
As
Integer
dmPaperWidth
As
Integer
dmScale
As
Integer
dmCopies
As
Integer
dmDefaultSource
As
Integer
dmPrintQuality
As
Integer
dmColor
As
Integer
dmDuplex
As
Integer
dmYResolution
As
Integer
dmTTOption
As
Integer
dmCollate
As
Integer
dmFormName
As
String
*
CCFORMNAME
dmUnusedPadding
As
Integer
dmBitsPerPel
As
Integer
dmPelsWidth
As
Long
dmPelsHeight
As
Long
dmDisplayFlags
As
Long
dmDisplayFrequency
As
Long
End
Type
Private
Sub
cmdChangeDesktopMode_Click()
Dim
DM
As
DEVMODE
With
DM
.dmPelsWidth
=
CInt(txtNewWidth.Text)
.dmPelsHeight
=
CInt(txtNewHeight.Text)
.dmBitsPerPel
=
CInt(txtNewColor.Text)
.dmDisplayFrequency
=
CInt(txtNewFreq.Text)
.dmFields
=
DM_PELSWIDTH
Or
DM_PELSHEIGHT
Or
DM_BITSPERPEL
Or
DM_DISPLAYFREQUENCY
.dmSize
=
LenB(DM)
End
With
If
ChangeDisplaySettings(DM,
CDS_FORCE)
Then
MsgBox
"错误!不支持此模式！"
End
If
End
Sub
Private
Sub
Form_Load()
txtOldWidth.Text
=
GetDeviceCaps(Me.hdc,
HORZRES)
txtOldHeight.Text
=
GetDeviceCaps(Me.hdc,
VERTRES)
txtOldColor.Text
=
GetDeviceCaps(Me.hdc,
BITSPIXEL)
txtOldFreq.Text
=
GetDeviceCaps(Me.hdc,
VREFRESH)
End
Sub
保存前加一句 myImage2.SetResolution(300, 300) 你设置的bMape不是保存的主画布 所以无效，设置分辨率就是 SetResolution（X,Y）