/// <inheritdoc/>
protected override void OnFrameApply(ImageFrame <TPixel> source)
{
TPixel upperColor = this.definition.UpperColor.ToPixel <TPixel>();
TPixel lowerColor = this.definition.LowerColor.ToPixel <TPixel>();
IErrorDiffuser diffuser = this.definition.Diffuser;
byte threshold = (byte)MathF.Round(this.definition.Threshold * 255F);
bool isAlphaOnly = typeof(TPixel) == typeof(A8);
var interest = Rectangle.Intersect(this.SourceRectangle, source.Bounds());
int startY = interest.Y;
int endY = interest.Bottom;
int startX = interest.X;
int endX = interest.Right;
// Collect the values before looping so we can reduce our calculation count for identical sibling pixels
TPixel sourcePixel = source[startX, startY];
TPixel previousPixel = sourcePixel;
Rgba32 rgba = default;
sourcePixel.ToRgba32(ref rgba);
// Convert to grayscale using ITU-R Recommendation BT.709 if required
byte luminance = isAlphaOnly ? rgba.A : ImageMaths.Get8BitBT709Luminance(rgba.R, rgba.G, rgba.B);
for (int y = startY; y < endY; y++)
{
Span <TPixel> row = source.GetPixelRowSpan(y);
for (int x = startX; x < endX; x++)
{
sourcePixel = row[x];
// Check if this is the same as the last pixel. If so use that value
// rather than calculating it again. This is an inexpensive optimization.
if (!previousPixel.Equals(sourcePixel))
{
sourcePixel.ToRgba32(ref rgba);
luminance = isAlphaOnly ? rgba.A : ImageMaths.Get8BitBT709Luminance(rgba.R, rgba.G, rgba.B);
// Setup the previous pointer
previousPixel = sourcePixel;
}
TPixel transformedPixel = luminance >= threshold ? upperColor : lowerColor;
diffuser.Dither(source, sourcePixel, transformedPixel, x, y, startX, endX, endY);
}
}
}
