/// <summary>
/// ドロップシャドウを加えた新しいビットマップを作成します。
/// </summary>
/// <param name="srcBmp">対象のビットマップ</param>
/// <param name="blur">ぼかし</param>
/// <param name="distance">影の距離</param>
/// <param name="shadowColor">影の色</param>
/// <param name="baseOffset">描画先オフセット値の格納先</param>
/// <returns>ドロップシャドウが加えられた新しいビットマップ</returns>
private static Bitmap AppendDropShadow(Bitmap srcBmp, int blur, Point distance, Color shadowColor, out Point baseOffset)
{
baseOffset = new Point(0, 0);
if (srcBmp == null || blur < 0)
{
return null;
}
Rectangle srcRect = new Rectangle(0, 0, srcBmp.Width, srcBmp.Height);
Rectangle shadowRect = srcRect;
shadowRect.Offset(distance.X, distance.Y);
Rectangle shadowBlurRect = shadowRect;
shadowBlurRect.Inflate(blur, blur);
Rectangle destRect = Rectangle.Union(srcRect, shadowBlurRect);
baseOffset.X = destRect.X - srcRect.X;
baseOffset.Y = destRect.Y - srcRect.Y;
Bitmap destBmp = new Bitmap(destRect.Width, destRect.Height, PixelFormat.Format32bppArgb);
BitmapData destBmpData = destBmp.LockBits(new Rectangle(0, 0, destRect.Width, destRect.Height), ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
BitmapData srcBmpData = srcBmp.LockBits(srcRect, ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
unsafe
{
byte* destLine = (byte*)destBmpData.Scan0 + (shadowBlurRect.Y - destRect.Y) * destBmpData.Stride + (shadowBlurRect.X - destRect.X) * 4;
byte* srcBeginLine = (byte*)srcBmpData.Scan0 + (- blur - blur) * srcBmpData.Stride + (- blur - blur) * 4;
int destWidth = shadowBlurRect.Width;
int destHeight = shadowBlurRect.Height;
int srcWidth = srcBmp.Width;
int srcHeight = srcBmp.Height;
int div = (1 + blur + blur) * (1 + blur + blur);
byte r = shadowColor.R;
byte g = shadowColor.G;
byte b = shadowColor.B;
float alpha = shadowColor.A / 255.0f;
int destStride = destBmpData.Stride;
int srcStride = srcBmpData.Stride;
for (int destY = 0; destY < destHeight; destY++, destLine += destStride, srcBeginLine += srcStride)
{
byte* dest = destLine;
byte* srcBegin = srcBeginLine;
for (int destX = 0; destX < destWidth; destX++, dest += 4, srcBegin += 4)
{
int total = 0;
byte* srcLine = srcBegin;
for (int srcY = destY - blur - blur; srcY <= destY; srcY++, srcLine += srcStride)
{
if (srcY >= 0 && srcY < srcHeight)
{
byte* src = srcLine;
for (int srcX = destX - blur - blur; srcX <= destX; srcX++, src += 4)
{
if (srcX >= 0 && srcX < srcWidth)
{
total += src[3];
}
}
}
}
dest[0] = b;
dest[1] = g;
dest[2] = r;
dest[3] = (byte)((total / div) * alpha);
}
}
}
srcBmp.UnlockBits(srcBmpData);
destBmp.UnlockBits(destBmpData);
using (Graphics g = Graphics.FromImage(destBmp))
{
g.DrawImage(srcBmp, srcRect.X - destRect.X, srcRect.Y - destRect.Y, srcBmp.Width, srcBmp.Height);
}
return destBmp;
}
