public void FasAbsResultMatchesMath()
{
const int X = -33;
int expected = Math.Abs(X);
Assert.Equal(expected, ImageMaths.FastAbs(X));
}
/// <summary>
/// Get the a pixel row at a given position with a length of the tile width. Mirrors pixels which exceeds the edges.
/// </summary>
/// <param name="source">The source image.</param>
/// <param name="rowPixels">Pre-allocated pixel row span of the size of a the tile width.</param>
/// <param name="x">The x position.</param>
/// <param name="y">The y position.</param>
/// <param name="tileWidth">The width in pixels of a tile.</param>
/// <param name="configuration">The configuration.</param>
private void CopyPixelRow(
ImageFrame <TPixel> source,
Span <Vector4> rowPixels,
int x,
int y,
int tileWidth,
Configuration configuration)
{
if (y < 0)
{
y = ImageMaths.FastAbs(y);
}
else if (y >= source.Height)
{
int diff = y - source.Height;
y = source.Height - diff - 1;
}
// Special cases for the left and the right border where GetPixelRowSpan can not be used.
if (x < 0)
{
rowPixels.Clear();
int idx = 0;
for (int dx = x; dx < x + tileWidth; dx++)
{
rowPixels[idx] = source[ImageMaths.FastAbs(dx), y].ToVector4();
idx++;
}
return;
}
else if (x + tileWidth > source.Width)
{
rowPixels.Clear();
int idx = 0;
for (int dx = x; dx < x + tileWidth; dx++)
{
if (dx >= source.Width)
{
int diff = dx - source.Width;
rowPixels[idx] = source[dx - diff - 1, y].ToVector4();
}
else
{
rowPixels[idx] = source[dx, y].ToVector4();
}
idx++;
}
return;
}
this.CopyPixelRowFast(source, rowPixels, x, y, tileWidth, configuration);
}
/// <summary>
/// Computes a simple linear function of the three neighboring pixels (left, above, upper left), then chooses
/// as predictor the neighboring pixel closest to the computed value.
/// </summary>
/// <param name="left">The left neighbor pixel.</param>
/// <param name="above">The above neighbor pixel.</param>
/// <param name="upperLeft">The upper left neighbor pixel.</param>
/// <returns>
/// The <see cref="byte"/>.
/// </returns>
private static byte PaethPredicator(byte left, byte above, byte upperLeft)
{
int p = left + above - upperLeft;
int pa = ImageMaths.FastAbs(p - left);
int pb = ImageMaths.FastAbs(p - above);
int pc = ImageMaths.FastAbs(p - upperLeft);
if (pa <= pb && pa <= pc)
{
return(left);
}
if (pb <= pc)
{
return(above);
}
return(upperLeft);
}