Premultiplied alpha content processor

Originally posted to Shawn Hargreaves Blog on MSDN, Wednesday, November 11, 2009

As mentioned in my previous post, a Content Processor that converts textures into premultiplied alpha format:

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content.Pipeline;
using Microsoft.Xna.Framework.Content.Pipeline.Graphics;
using Microsoft.Xna.Framework.Content.Pipeline.Processors;

namespace PremultipliedAlpha
{
    [ContentProcessor]
    class PremultipliedAlphaTextureProcessor : TextureProcessor
    {
        public override TextureContent Process(TextureContent input, ContentProcessorContext context)
        {
            input.ConvertBitmapType(typeof(PixelBitmapContent<Color>));

            foreach (MipmapChain mipChain in input.Faces)
            {
                foreach (PixelBitmapContent<Color> bitmap in mipChain)
                {
                    for (int y = 0; y < bitmap.Height; y++)
                    {
                        for (int x = 0; x < bitmap.Width; x++)
                        {
                            Color c = bitmap.GetPixel(x, y);

                            c.R = (byte)(c.R * c.A / 255);
                            c.G = (byte)(c.G * c.A / 255);
                            c.B = (byte)(c.B * c.A / 255);

                            bitmap.SetPixel(x, y, c);
                        }
                    }
                }
            }

            return base.Process(input, context);
        }
    }
}