C# 像素与毫米转化，GDI画图显示实际尺寸.

#region Win32 API
[DllImport("user32.dll")]
static extern IntPtr GetDC(IntPtr ptr);
[DllImport("gdi32.dll")]
static extern int GetDeviceCaps(
IntPtr hdc, // handle to DC
int nIndex // index of capability
);
[DllImport("user32.dll", EntryPoint = "ReleaseDC")]
static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDc);
#endregion

#region DeviceCaps常量
const int HORZRES = 8;
const int VERTRES = 10;
const int LOGPIXELSX = 88;
const int LOGPIXELSY = 90;
const int DESKTOPVERTRES = 117;
const int DESKTOPHORZRES = 118;
#endregion

#region 属性
/// <summary>
/// 宽度转化 length是毫米，1厘米=10毫米
/// </summary>
/// <param name="length"></param>
/// <returns></returns>
public static double MillimetersToPixelsWidth(double length)
{
System.Windows.Forms.Panel p = new System.Windows.Forms.Panel();
System.Drawing.Graphics g = System.Drawing.Graphics.FromHwnd(p.Handle);
IntPtr hdc = g.GetHdc();
int width = GetDeviceCaps(hdc, 4); // HORZRES
int pixels = GetDeviceCaps(hdc, 8); // BITSPIXEL
double fg = pixels / width;
g.ReleaseHdc(hdc);
return (((double)pixels / (double)width) * (double)length);
}

/// <summary>
/// 高度转化 length是毫米，1厘米=10毫米
/// </summary>
/// <param name="length"></param>
/// <returns></returns>
public static double MillimetersToPixelsHeight(double length)
{
System.Windows.Forms.Panel p = new System.Windows.Forms.Panel();
System.Drawing.Graphics g = System.Drawing.Graphics.FromHwnd(p.Handle);
IntPtr hdc = g.GetHdc();
int height = GetDeviceCaps(hdc, 6); // HORZRES
int pixels = GetDeviceCaps(hdc, 10); // BITSPIXEL
double fg = pixels / height;
g.ReleaseHdc(hdc);
return (((double)pixels / (double)height) * (double)length);
}

/// <summary>
/// 获取屏幕分辨率当前物理大小
/// </summary>
public static Size WorkingArea
{
get
{
IntPtr hdc = GetDC(IntPtr.Zero);
Size size = new Size();
size.Width = GetDeviceCaps(hdc, HORZRES);
size.Height = GetDeviceCaps(hdc, VERTRES);
ReleaseDC(IntPtr.Zero, hdc);
return size;
}
}
/// <summary>
/// 当前系统DPI_X 大小 一般为96
/// </summary>
public static int DpiX
{
get
{
IntPtr hdc = GetDC(IntPtr.Zero);
int DpiX = GetDeviceCaps(hdc, LOGPIXELSX);
ReleaseDC(IntPtr.Zero, hdc);
return DpiX;
}
}
/// <summary>
/// 当前系统DPI_Y 大小 一般为96
/// </summary>
public static int DpiY
{
get
{
IntPtr hdc = GetDC(IntPtr.Zero);
int DpiX = GetDeviceCaps(hdc, LOGPIXELSY);
ReleaseDC(IntPtr.Zero, hdc);
return DpiX;
}
}
/// <summary>
/// 获取真实设置的桌面分辨率大小
/// </summary>
public static Size DESKTOP
{
get
{
IntPtr hdc = GetDC(IntPtr.Zero);
Size size = new Size();
size.Width = GetDeviceCaps(hdc, DESKTOPHORZRES);
size.Height = GetDeviceCaps(hdc, DESKTOPVERTRES);
ReleaseDC(IntPtr.Zero, hdc);
return size;
}
}

/// <summary>
/// 获取宽度缩放百分比
/// </summary>
public static float ScaleX
{
get
{
IntPtr hdc = GetDC(IntPtr.Zero);
int t = GetDeviceCaps(hdc, DESKTOPHORZRES);
int d = GetDeviceCaps(hdc, HORZRES);
float ScaleX = (float)GetDeviceCaps(hdc, DESKTOPHORZRES) / (float)GetDeviceCaps(hdc, HORZRES);
ReleaseDC(IntPtr.Zero, hdc);
return ScaleX;
}
}

/// <summary>
/// 获取高度缩放百分比
/// </summary>
public static float ScaleY
{
get
{
IntPtr hdc = GetDC(IntPtr.Zero);
float ScaleY = (float)(float)GetDeviceCaps(hdc, DESKTOPVERTRES) / (float)GetDeviceCaps(hdc, VERTRES);
ReleaseDC(IntPtr.Zero, hdc);
return ScaleY;
}
}
#endregion