hi all

i included the sources of my form.
when run, u can open a bmp file.
once opened, and resized,
u will see that the image is upside down.

can someone please tell me why this is happening?

tnx
assaf

the code:

using System;
using System.Runtime.InteropServices;
using System.Drawing;
using System.Drawing.Imaging;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;

namespace WindowsApplication3
{
/// <summary>
/// Summary description for Form1.
/// </summary>
public class Form1 : System.Windows.Forms.Form
{
 private System.Windows.Forms.OpenFileDialog openFileDialog1;
 private System.Windows.Forms.MainMenu mainMenu1;
 private System.Windows.Forms.MenuItem menuItem1;
 private System.Windows.Forms.MenuItem menuItemOpen;
 /// <summary>
 /// Required designer variable.
 /// </summary>
 private System.ComponentModel.Container components = null;

 public Form1()
 {
  //
  // Required for Windows Form Designer support
  //
  InitializeComponent();

  //
  // TODO: Add any constructor code after InitializeComponent call
  //
 }

 /// <summary>
 /// Clean up any resources being used.
 /// </summary>
 protected override void Dispose( bool disposing )
 {
  if( disposing )
  {
   if (components != null)
   {
    components.Dispose();
   }
  }
  base.Dispose( disposing );
 }

 #region Windows Form Designer generated code
 /// <summary>
 /// Required method for Designer support - do not modify
 /// the contents of this method with the code editor.
 /// </summary>
 private void InitializeComponent()
 {
  this.openFileDialog1 = new System.Windows.Forms.OpenFileDialog();
  this.mainMenu1 = new System.Windows.Forms.MainMenu();
  this.menuItem1 = new System.Windows.Forms.MenuItem();
  this.menuItemOpen = new System.Windows.Forms.MenuItem();
  //
  // openFileDialog1
  //
  this.openFileDialog1.FileOk += new
System.ComponentModel.CancelEventHandler(this.openFileDialog1_FileOk);
  //
  // mainMenu1
  //
  this.mainMenu1.MenuItems.AddRange(new System.Windows.Forms.MenuItem[] {
                      this.menuItem1});
  //
  // menuItem1
  //
  this.menuItem1.Index = 0;
  this.menuItem1.MenuItems.AddRange(new System.Windows.Forms.MenuItem[] {
                      this.menuItemOpen});
  this.menuItem1.Text = "&File";
  //
  // menuItemOpen
  //
  this.menuItemOpen.Index = 0;
  this.menuItemOpen.Text = "&Open...";
  this.menuItemOpen.Click += new
System.EventHandler(this.menuItemOpen_Click);
  //
  // Form1
  //
  this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
  this.AutoScroll = true;
  this.AutoScrollMinSize = new System.Drawing.Size(1124, 868);
  this.ClientSize = new System.Drawing.Size(276, 257);
  this.Menu = this.mainMenu1;
  this.Name = "Form1";
  this.Text = "Form1";
  this.Paint += new
System.Windows.Forms.PaintEventHandler(this.Form1_Paint);

 }
 #endregion

 /// <summary>
 /// The main entry point for the application.
 /// </summary>
 [STAThread]
 static void Main()
 {
  Application.Run(new Form1());
 }

 private void DrawDIB(IntPtr hdc, int XDest, int YDest, int DestWidth, int
DestHeight, int XSrc, int YSrc, int SrcWidth, int SrcHeight, uint rop)
 {
  Bitmap b = (Bitmap)this._Image;
  BitmapData bm = null;
  try
  {
   Rectangle r = new Rectangle(XSrc, YSrc, SrcWidth, SrcHeight);
   bm = b.LockBits(r, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
   uint iStretchDIBits = Gdi32.StretchDIBits(hdc, XDest, YDest, DestWidth,
DestHeight, XSrc, YSrc, SrcWidth, SrcHeight, bm.Scan0, this._BITMAPINFO,
DIB_RGB_COLORS, rop);
   if(iStretchDIBits == Gdi32.GDI_ERROR)
   {
    throw new ApplicationException("StretchDIBits Failed");
   }
  }
  finally
  {
   if(bm != null)
   {
    b.UnlockBits(bm);
   }
  }
 }

 private void Form1_Paint(object sender,
System.Windows.Forms.PaintEventArgs e)
 {
  if(this._Image != null)
  {
   IntPtr hdc = e.Graphics.GetHdc();

   Gdi32.SetWindowOrgEx(hdc, 0, 0, IntPtr.Zero);
   int horiz = - User32.GetScrollPos(this.Handle,
User32.ScrollPos.SB_HORZ);
   int vert =  - User32.GetScrollPos(this.Handle,
User32.ScrollPos.SB_VERT);
   Gdi32.SetViewportOrgEx(hdc, horiz, vert, IntPtr.Zero);

   int iSaveDC = Gdi32.SaveDC(hdc);
   int w = this._Image.Width;
   int h = this._Image.Height;
   this.DrawDIB(hdc, GAP, GAP, w, h, 0, 0, w, h, SRCCOPY);

   bool bRestoreDC = Gdi32.RestoreDC(hdc, -1);
   if(bRestoreDC == false)
   {
    throw new ApplicationException("RestoreDC Failed");
   }
   e.Graphics.ReleaseHdc(hdc);
  }
 }

 private const int DIB_RGB_COLORS = 0; // color table in RGBs
 private const int SRCCOPY = 0x00CC0020; // dest = source
 private const int GAP = 16;
 private Image _Image;
 private Gdi32.BITMAPINFO _BITMAPINFO = new Gdi32.BITMAPINFO();

 private void openFileDialog1_FileOk(object sender,
System.ComponentModel.CancelEventArgs e)
 {
  this._BITMAPINFO.bmiColors.rgbBlue  = 200;
  this._BITMAPINFO.bmiColors.rgbGreen  = 208;
  this._BITMAPINFO.bmiColors.rgbRed  = 212;
  this._BITMAPINFO.bmiColors.rgbReserved = 200;

  this._BITMAPINFO.bmiHeader.biSize   = 40;
  this._BITMAPINFO.bmiHeader.biWidth   = 1024;
  this._BITMAPINFO.bmiHeader.biHeight   = 768;
  this._BITMAPINFO.bmiHeader.biPlanes   = 1;
  this._BITMAPINFO.bmiHeader.biBitCount  = 24;
  this._BITMAPINFO.bmiHeader.biCompression = 0;
  this._BITMAPINFO.bmiHeader.biSizeImage  = 2359296;
  this._BITMAPINFO.bmiHeader.biXPelsPerMeter = 0;
  this._BITMAPINFO.bmiHeader.biYPelsPerMeter = 0;
  this._BITMAPINFO.bmiHeader.biClrUsed  = 0;
  this._BITMAPINFO.bmiHeader.biClrImportant = 0;

  this._Image = Image.FromFile(this.openFileDialog1.FileName);
 }

 private void menuItemOpen_Click(object sender, System.EventArgs e)
 {
  this.openFileDialog1.ShowDialog(this);
 }

 private class User32
 {
  internal enum ScrollPos
  {
   SB_HORZ = 0,
   SB_VERT = 1
  }

  [DllImport("user32.dll")]
  internal static extern
   int GetScrollPos(
   IntPtr hWnd,
   ScrollPos nBar
   );
 }

 private class Gdi32
 {
  [DllImport("gdi32.dll")]
  internal static extern
   bool SetViewportOrgEx(
   IntPtr hdc,        // handle to device context
   int X,          // new x-coordinate of viewport origin
   int Y,          // new y-coordinate of viewport origin
   IntPtr lpPoint // original viewport origin
   );

  [DllImport("gdi32.dll")]
  internal static extern
   bool SetWindowOrgEx(
   IntPtr hdc,        // handle to device context
   int X,          // new x-coordinate of window origin
   int Y,          // new y-coordinate of window origin
   IntPtr lpPoint // original window origin
   );

  [StructLayout(LayoutKind.Sequential)]
  internal struct BITMAPINFOHEADER
  {
   public uint   biSize;
   public int    biWidth;
   public int    biHeight;
   public short  biPlanes;
   public short  biBitCount;
   public uint   biCompression;
   public uint   biSizeImage;
   public int    biXPelsPerMeter;
   public int    biYPelsPerMeter;
   public uint   biClrUsed;
   public uint   biClrImportant;
  }

  [StructLayout(LayoutKind.Sequential)]
  internal struct RGBQUAD
  {
   public byte    rgbBlue;
   public byte    rgbGreen;
   public byte    rgbRed;
   public byte    rgbReserved;
  }

  [StructLayout(LayoutKind.Sequential)]
  internal class BITMAPINFO
  {
   public BITMAPINFOHEADER bmiHeader;

   //[MarshalAs(UnmanagedType.ByValArray, SizeConst = 1)]
   //public RGBQUAD [] bmiColors = new RGBQUAD[1];
   public RGBQUAD bmiColors;
  }

  [DllImport("gdi32.dll")]
  internal static extern
   uint StretchDIBits(
   IntPtr /*HDC*/ hdc,                     // handle to DC
   int XDest,                       // x-coord of destination upper-left
corner
   int YDest,                       // y-coord of destination upper-left
corner
   int nDestWidth,                  // width of destination rectangle
   int nDestHeight,                 // height of destination rectangle
   int XSrc,                        // x-coord of source upper-left corner
   int YSrc,                        // y-coord of source upper-left corner
   int nSrcWidth,                   // width of source rectangle
   int nSrcHeight,                  // height of source rectangle
   IntPtr /*CONST VOID **/lpBits,   // bitmap bits
   BITMAPINFO /*CONST BITMAPINFO **/lpBitsInfo,// bitmap data
   uint iUsage,                    // usage options
   uint dwRop                      // raster operation code
   );

  internal const uint GDI_ERROR = 0xFFFFFFFF;

  [DllImport("gdi32.dll")]
  internal static extern
   bool RestoreDC(
   IntPtr /*HDC*/ hdc,       // handle to DC
   int nSavedDC   // restore state
   );

  [DllImport("gdi32.dll")]
  internal static extern
   int SaveDC(
   /*HDC*/IntPtr hdc   // handle to DC
   );
 }
}
}