/// <summary> Attenuate the specified bitmap.
///
/// </summary>
/// <param name="bm">Bitmap to attenuate
/// </param>
/// <param name="xpos">horizontal position
/// </param>
/// <param name="ypos">vertical position
/// </param>
public virtual void Attenuate(Bitmap bm, int xpos, int ypos)
{
// Check
// Compute number of rows and columns
int xrows = ypos + bm.ImageHeight;
if (xrows > ImageHeight)
{
xrows = ImageHeight;
}
if (ypos > 0)
{
xrows -= ypos;
}
int xcolumns = xpos + bm.ImageWidth;
if (xcolumns > ImageWidth)
{
xcolumns = ImageWidth;
}
if (xpos > 0)
{
xcolumns -= xpos;
}
if ((xrows <= 0) || (xcolumns <= 0))
{
return;
}
// Precompute multiplier map
int maxgray = bm.Grays - 1;
int[] multiplier = GetMultiplier(maxgray);
// Compute starting point
int src = bm.RowOffset((ypos < 0) ? (-ypos) : 0) - ((xpos < 0) ? xpos : 0);
int dst = RowOffset((ypos > 0) ? ypos : 0) + ((xpos > 0) ? xpos : 0);
PixelReference dstPixel = CreateGPixelReference(0);
// Loop over rows
for (int y = 0; y < xrows; y++)
{
// Loop over columns
dstPixel.SetOffset(dst);
for (int x = 0; x < xcolumns; dstPixel.IncOffset())
{
int srcpix = bm.GetByteAt(src + (x++));
// Perform pixel operation
if (srcpix > 0)
{
if (srcpix >= maxgray)
{
dstPixel.SetGray(0);
}
else
{
int level = multiplier[srcpix];
dstPixel.SetBGR((dstPixel.Blue * level) >> 16, (dstPixel.Green * level) >> 16,
(dstPixel.Red * level) >> 16);
}
}
}
// Next line
dst += GetRowSize();
src += bm.GetRowSize();
}
}