/// <summary>
/// Superimposes one bitmap onto another.
/// </summary>
/// <param name="backBmpData">BitmapData from the bitmap to be drawn onto.</param>
/// <param name="frontBmp">Bitmap to draw from.</param>
/// <param name="transparent">Whether or not transparency is desired.</param>
/// <param name="point">Point on the back bitmap to copy the front bitmap.</param>
public static void Superimpose(BitmapData backBmpData, Bitmap frontBmp, bool transparent, Point point)
{
//Currently only supports Format24bppRgb and Format32bppArgb.
if ((backBmpData.PixelFormat != PixelFormat.Format24bppRgb && backBmpData.PixelFormat != PixelFormat.Format32bppArgb) ||
(frontBmp.PixelFormat != PixelFormat.Format24bppRgb && frontBmp.PixelFormat != PixelFormat.Format32bppArgb))
{
throw new Exception("Currently only supports Format24bppRgb and Format32bppArgb.");
}
//If the point is not contained in the back bitmap then we return doing nothing as that is implicitly performing the out of bounds superimposition.
if (backBmpData.Width <= point.X || backBmpData.Height <= point.Y)
{
return;
}
Size size = SuperimposerHelper.GetFrontBmpSize(frontBmp, point, backBmpData.Width, backBmpData.Height);
BitmapData frontBmpData = frontBmp.LockBits(new Rectangle(0, 0, frontBmp.Width, frontBmp.Height), ImageLockMode.ReadOnly, frontBmp.PixelFormat);
if (transparent && frontBmp.PixelFormat == PixelFormat.Format32bppArgb)
{
Blend(backBmpData, frontBmpData, point, size);
}
else
{
Copy(backBmpData, frontBmpData, point, size);
}
frontBmp.UnlockBits(frontBmpData);
}
/// <summary>
/// Blends one bitmap into another using alpha blending.
/// </summary>
/// <param name="backBmpData">BitmapData from the bitmap to be drawn onto.</param>
/// <param name="frontBmpData">BitmapData from the bitmap to draw from.</param>
/// <param name="point">Point on the back bitmap to copy the front bitmap.</param>
/// <param name="size">Size of the subset of pixels to use from the front bitmap.</param>
private static void Blend(BitmapData backBmpData, BitmapData frontBmpData, Point point, Size size)
{
unsafe
{
//Bpp of each bitmap may be different.
int backBpp = Bitmap.GetPixelFormatSize(backBmpData.PixelFormat) / 8;
int frontBpp = Bitmap.GetPixelFormatSize(frontBmpData.PixelFormat) / 8;
int pointX = point.X;
int pointY = point.Y;
int sizeHeight = size.Height;
int frontStride = frontBmpData.Stride;
int frontSizeStride = size.Width * frontBpp;
byte *frontBmpDataScan0 = (byte *)frontBmpData.Scan0;
int backStride = backBmpData.Stride;
byte *backBmpDataScan0 = (byte *)backBmpData.Scan0;
//Need to handle two cases where the back bitmap is Format24bppRgb or Format32bppArgb.
//Lots of duplicate code because handling this nested in loops will cause degraded performance.
if (backBmpData.PixelFormat == PixelFormat.Format24bppRgb)
{
//Iterate through each row of pixels in parallel.
Parallel.For(0, sizeHeight, y =>
{
byte *backRow = backBmpDataScan0 + ((y + pointY) * backStride);
byte *frontRow = frontBmpDataScan0 + (y * frontStride);
int backRowByte = pointX * backBpp;
int frontRowByte = 0;
//Iterate through the pixels in the rows. Should only need to check one condition as the same amount of pixels should be traversed in both bitmaps.
for (; frontRowByte < frontSizeStride; backRowByte += backBpp, frontRowByte += frontBpp)
{
int alpha = frontRow[frontRowByte + 3] + 1;
int invAlpha = 256 - frontRow[frontRowByte + 3];
backRow[backRowByte] = (byte)((alpha * frontRow[frontRowByte] + invAlpha * backRow[backRowByte]) >> 8);
backRow[backRowByte + 1] = (byte)((alpha * frontRow[frontRowByte + 1] + invAlpha * backRow[backRowByte + 1]) >> 8);
backRow[backRowByte + 2] = (byte)((alpha * frontRow[frontRowByte + 2] + invAlpha * backRow[backRowByte + 2]) >> 8);
}
});
}
if (backBmpData.PixelFormat == PixelFormat.Format32bppArgb)
{
//Iterate through each row of pixels in parallel.
Parallel.For(0, sizeHeight, y =>
{
byte *backRow = backBmpDataScan0 + ((y + pointY) * backStride);
byte *frontRow = frontBmpDataScan0 + (y * frontStride);
int backRowByte = pointX * backBpp;
int frontRowByte = 0;
//Iterate through the pixels in the rows. Should only need to check one condition as the same amount of pixels should be traversed in both bitmaps.
for (; frontRowByte < frontSizeStride; backRowByte += backBpp, frontRowByte += frontBpp)
{
int frontAlphaByte = frontRow[frontRowByte + 3];
int inverseFrontAlphaByte = frontRow[frontRowByte + 3];
int backAlphaByte = (backRow[backRowByte + 3]);
float backAlpha = backAlphaByte / 255f;
float frontAlpha = frontAlphaByte / 255f;
float inverseFrontAlpha = 1 - frontAlpha;
float blendedAlpha = (backAlpha + (1 - backAlpha) * frontAlpha);
backRow[backRowByte] = SuperimposerHelper.Clamp((frontRow[frontRowByte] * frontAlpha + backRow[backRowByte] * backAlpha * inverseFrontAlpha) / blendedAlpha);
backRow[backRowByte + 1] = SuperimposerHelper.Clamp((frontRow[frontRowByte + 1] * frontAlpha + backRow[backRowByte + 1] * backAlpha * inverseFrontAlpha) / blendedAlpha);
backRow[backRowByte + 2] = SuperimposerHelper.Clamp((frontRow[frontRowByte + 2] * frontAlpha + backRow[backRowByte + 2] * backAlpha * inverseFrontAlpha) / blendedAlpha);
backRow[backRowByte + 3] = SuperimposerHelper.Clamp(255 * blendedAlpha);
}
});
}
}
}
