/// <summary>
/// Implements bicubic filtering with bounds checking at every pixel.
/// </summary>
private unsafe void BicubicFitSurfaceChecked(MaskSurface source, Rectangle dstRoi)
{
Rectangle roi = Rectangle.Intersect(dstRoi, Bounds);
Rectangle roiIn = Rectangle.Intersect(dstRoi, new Rectangle(1, 1, width - 1, height - 1));
IntPtr rColCacheIP = Memory.Allocate(4 * (long)roi.Width * (long)sizeof(double), false);
double *rColCache = (double *)rColCacheIP.ToPointer();
// Precompute and then cache the value of R() for each column
for (int dstX = roi.Left; dstX < roi.Right; ++dstX)
{
double srcColumn = (double)(dstX * (source.width - 1)) / (double)(width - 1);
double srcColumnFloor = Math.Floor(srcColumn);
double srcColumnFrac = srcColumn - srcColumnFloor;
for (int m = -1; m <= 2; ++m)
{
int index = (m + 1) + ((dstX - roi.Left) * 4);
double x = m - srcColumnFrac;
rColCache[index] = R(x);
}
}
// Set this up so we can cache the R()'s for every row
double *rRowCache = stackalloc double[4];
for (int dstY = roi.Top; dstY < roi.Bottom; ++dstY)
{
double srcRow = (double)(dstY * (source.height - 1)) / (double)(height - 1);
double srcRowFloor = (double)Math.Floor(srcRow);
double srcRowFrac = srcRow - srcRowFloor;
int srcRowInt = (int)srcRow;
byte * dstPtr = GetPointAddressUnchecked(roi.Left, dstY);
// Compute the R() values for this row
for (int n = -1; n <= 2; ++n)
{
double x = srcRowFrac - n;
rRowCache[n + 1] = R(x);
}
// See Perf Note below
//int nFirst = Math.Max(-srcRowInt, -1);
//int nLast = Math.Min(source.height - srcRowInt - 1, 2);
for (int dstX = roi.Left; dstX < roi.Right; dstX++)
{
double srcColumn = (double)(dstX * (source.width - 1)) / (double)(width - 1);
double srcColumnFloor = Math.Floor(srcColumn);
double srcColumnFrac = srcColumn - srcColumnFloor;
int srcColumnInt = (int)srcColumn;
double graySum = 0;
double alphaSum = 0;
double totalWeight = 0;
// See Perf Note below
//int mFirst = Math.Max(-srcColumnInt, -1);
//int mLast = Math.Min(source.width - srcColumnInt - 1, 2);
byte *srcPtr = source.GetPointAddressUnchecked(srcColumnInt - 1, srcRowInt - 1);
for (int n = -1; n <= 2; ++n)
{
int srcY = srcRowInt + n;
for (int m = -1; m <= 2; ++m)
{
// Perf Note: It actually benchmarks faster on my system to do
// a bounds check for every (m,n) than it is to limit the loop
// to nFirst-Last and mFirst-mLast.
// I'm leaving the code above, albeit commented out, so that
// benchmarking between these two can still be performed.
if (source.IsVisible(srcColumnInt + m, srcY))
{
double w0 = rColCache[(m + 1) + (4 * (dstX - roi.Left))];
double w1 = rRowCache[n + 1];
double w = w0 * w1;
graySum += *srcPtr * w * 255.0;
alphaSum += 255.0 * w;
totalWeight += w;
}
++srcPtr;
}
srcPtr = ((byte *)(srcPtr - 4) + source.stride);
}
double alpha = alphaSum / totalWeight;
double gray;
if (alpha == 0)
{
gray = 0;
}
else
{
gray = graySum / alphaSum;
// add 0.5 to ensure truncation to uint results in rounding
gray += 0.5;
}
*dstPtr = (byte)gray;
++dstPtr;
} // for (dstX...
} // for (dstY...
Memory.Free(rColCacheIP);
}
