A question was asked on the mailing list (ages ago) about creating 8-bit GIF files. I proved this code for simple palette based GIFs, so here it is:
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;
namespace Project
{
class ProjectMain
{
public static void Main()
{
GenerateBackgroundImage(Color.AliceBlue, Color.Beige, Color.Cyan, 10, 10, 10, @"c:\image.gif");
}
public static void GenerateBackgroundImage(Color leftColour, Color centerColour,
Color rightColour, int leftWidth, int centerWidth, int rightWidth, string path)
{
int width = leftWidth + centerWidth + rightWidth + 2;
int height = 10;
using (Bitmap bitmap = new Bitmap(width, height, PixelFormat.Format8bppIndexed))
{
Color backColour = Color.White;
byte idxBackground = 0;
byte idxLeft = 1;
byte idxCenter = 2;
byte idxRight = 3;
ColorPalette cp = bitmap.Palette;
cp.Entries[idxBackground] = backColour;
cp.Entries[idxLeft] = leftColour;
cp.Entries[idxCenter] = centerColour;
cp.Entries[idxRight] = rightColour;
bitmap.Palette = cp;
fillrect(idxBackground, bitmap, new Rectangle(0, 0, width, height));
fillrect(idxLeft, bitmap, new Rectangle(0, 0, leftWidth, height));
fillrect(idxCenter, bitmap, new Rectangle(leftWidth + 1, 0, centerWidth, height));
fillrect(idxRight, bitmap, new Rectangle(leftWidth + 2 + centerWidth, 0, rightWidth, height));
bitmap.Save(path, ImageFormat.Gif);
}
}
static void fillrect(byte colorIndex, Bitmap b, Rectangle r)
{
BitmapData bmpData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.WriteOnly, b.PixelFormat);
// Get the address of the first line.
IntPtr ptr = bmpData.Scan0;
// Declare an array to hold the bytes of the bitmap.
// This code is specific to a bitmap with 8 bits index per pixels.
int bytes = b.Width * b.Height;
byte[] Values = new byte[bytes];
// Copy the RGB values into the array.
Marshal.Copy(ptr, Values, 0, bytes);
for (int y = r.Top; y < r.Bottom; y++)
{
for (int x = r.Left; x < r.Right; x++)
{
Values[(y * b.Width) + x] = colorIndex;
}
}
// Copy the values back to the bitmap
Marshal.Copy(Values, 0, ptr, bytes);
// Unlock the bits.
b.UnlockBits(bmpData);
}
}
}
I would change fillrect, to seperate out the locking, and Marshal calls, to CreateTempBuffer, FillTempBuffer, and WriteTempBuffer functions, if you were to use fillrect more than a couple times. But as it stands, the code is correct after each call.
