Tao Te KaChing
Workin' the cash register of the Great Tao

Device Independent Bitmaps, C#, and Me...REDUX!

Well, after using the previously posted code in some projects at work, some limitations arose quickly. The two biggest were support for 8-bit bitmaps, and support for both 5-5-5 and 5-6-5 16-bit bitmaps.

The new code looks like the following:

using System;

using System.Collections.Generic;

using System.Drawing;

using System.Drawing.Imaging;

using System.Runtime.InteropServices;

using System.IO;

namespace DIBitmaps

{

static public class DIB

{

// our BITMAPINFOHEADER struct, as per gdi

// use LayoutKind to make sure data is marshalled as we've laid it out

[StructLayout(LayoutKind.Sequential)]

public struct BITMAPINFOHEADER

{

public uint biSize;

public int biWidth;

public int biHeight;

public ushort biPlanes;

public ushort biBitCount;

public uint biCompression;

public uint biSizeImage;

public int biXPelsPerMeter;

public int biYPelsPerMeter;

public uint biClrUsed;

public uint biClrImportant;

//public void Init()

//{

// biSize = (uint)Marshal.SizeOf(this);

//}

}

public static Bitmap BitmapFromDIB(MemoryStream dib)

{

// get byte array of device independent bitmap

byte[] dibBytes = dib.ToArray();

// get the handle for the byte array and "pin" that memory (i.e. prevent

// garbage collector from gobbling it up right away)...

GCHandle hdl = GCHandle.Alloc(dibBytes, GCHandleType.Pinned);

// marshal our data into a BITMAPINFOHEADER struct per Win32

// definition of BITMAPINFOHEADER

BITMAPINFOHEADER dibHdr = (BITMAPINFOHEADER)Marshal.PtrToStructure

(hdl.AddrOfPinnedObject(), typeof(BITMAPINFOHEADER));

bool is555 = true;

Bitmap bmp = null;

if (dibHdr.biBitCount == 8)

{

// set our pointer to end of BITMAPINFOHEADER

Int64 jumpTo = hdl.AddrOfPinnedObject().ToInt64() + dibHdr.biSize;

bmp = new Bitmap(dibHdr.biWidth, dibHdr.biHeight, PixelFormat.Format8bppIndexed);

bmp.SetResolution((100f * (float)dibHdr.biXPelsPerMeter) / 2.54f,

(100f * (float)dibHdr.biYPelsPerMeter) / 2.54f);

// set the colors in our palette

ColorPalette palette = bmp.Palette;

IntPtr ptr = IntPtr.Zero;

int colors = (int)(dibBytes.Length - (bmp.Width * bmp.Height) - dibHdr.biSize);

for (int i = 0; i < 256; i++)

{

ptr = new IntPtr(jumpTo);

uint bmiColor = (uint)Marshal.ReadInt32(ptr);

int r = (int)((bmiColor & 0xFF0000) >> 16),

g = (int)((bmiColor & 0xFF00) >> 8),

b = (int)((bmiColor & 0xFF));

palette.Entries[i] = Color.FromArgb(r, g, b);

jumpTo += 4;

}

bmp.Palette = palette;

// now write the remaining bmp data to our bitmap

BitmapData _8bd = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height),

ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);

jumpTo -= hdl.AddrOfPinnedObject().ToInt64();

Marshal.Copy(dibBytes, (int)jumpTo, _8bd.Scan0, _8bd.Stride * _8bd.Height);

bmp.UnlockBits(_8bd);

}

else if ((dibHdr.biBitCount == 16) && (dibHdr.biCompression == 3))

{

Int64 jumpTo = (Int64)(dibHdr.biClrUsed * (uint)4 + dibHdr.biSize);

IntPtr ptr = new IntPtr(hdl.AddrOfPinnedObject().ToInt64() + jumpTo);

ushort redMask = (ushort)Marshal.ReadInt16(ptr);

ptr = new IntPtr(ptr.ToInt64() + (2 * Marshal.SizeOf(typeof(UInt16))));

ushort greenMask = (ushort)Marshal.ReadInt16(ptr);

ptr = new IntPtr(ptr.ToInt64() + (2 * Marshal.SizeOf(typeof(UInt16))));

ushort blueMask = (ushort)Marshal.ReadInt16(ptr);

is555 = ((redMask == 0x7C00) && (greenMask == 0x03E0) && (blueMask == 0x001F));

}

// go ahead and release the "pin" from our handle on that memory

hdl.Free();

// If the target device does not have one plane, or we're working with a bitmap other

// than a non-compressed (BI_RGB) bitmap, we're not gonna work woith it

if (dibHdr.biPlanes != 1 || (dibHdr.biCompression != 0 && dibHdr.biCompression != 3))

return null;

if (bmp == null)

{

// we need to know beforehand the pixel-depth of our bitmap

PixelFormat fmt = PixelFormat.Format24bppRgb;

switch (dibHdr.biBitCount)

{

case 32:

fmt = PixelFormat.Format32bppRgb;

break;

case 24:

fmt = PixelFormat.Format24bppRgb;

break;

case 16:

fmt = (is555) ? PixelFormat.Format16bppRgb555 :

PixelFormat.Format16bppRgb565;

break;

default:

return null;

}

// prepare for our output bitmap

bmp = new Bitmap(dibHdr.biWidth, dibHdr.biHeight, fmt);

// load our "empty" bitmap into memory and lock it for

// writing in the format we specified

BitmapData bd = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height),

ImageLockMode.WriteOnly, fmt);

// marshal our device independent bitmap data over to our output bitmap

Marshal.Copy(dibBytes, Marshal.SizeOf(dibHdr), bd.Scan0, bd.Stride * bd.Height);

// we're done marshalling, so release our bitmapdata lock

bmp.UnlockBits(bd);

}

if (dibHdr.biHeight > 0)

{

// DIB data is upside-down for some reason, so flip it

bmp.RotateFlip(RotateFlipType.RotateNoneFlipY);

}

// return our bitmap

return bmp;

}

}

}

The adjusted code can be downloaded here.

If you find any other issues, please let me know and I'll get it updated ASAP.

~ZagNUT


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