/// <summary>
/// Dither an image using Floyd-Steinberg's dither.
/// </summary>
/// <param name="src">The image buffer (RGBA pixels).</param>
/// <param name="srcPos">Initial position on the source buffer.</param>
/// <param name="width">The width of the image.</param>
/// <param name="height">The height of the image.</param>
/// <param name="stride">The distance, in bytes, between rows of the image buffer.</param>
private void DitherImage(byte[] src, int srcPos, int width, int height, int stride)
{
int srcCurrentPos = srcPos;
for (int y = 0; y < height; y++, srcCurrentPos += stride - width * 4)
{
for (int x = 0; x < width; x++, srcCurrentPos += 4)
{
ColorRGBA pixel = ColorRGBA.Read(src, srcCurrentPos);
ColorRGBA newPixel = TrimColor(pixel);
newPixel.Write(src, srcCurrentPos);
int errorR = pixel.Red - newPixel.Red;
int errorG = pixel.Green - newPixel.Green;
int errorB = pixel.Blue - newPixel.Blue;
int errorA = pixel.Alpha - newPixel.Alpha;
// Distributes error to pixel at (deltaX, deltaY) of current pixel, using the specified weight.
/* Floyd-Steinberg dither.
* Distributes the error at pixel X to neighboring pixels using those weights:
* -1 0 1
* /--------
* -1 | 0 0 0
* 0 | 0 X 7
* 1 | 3 5 1
*/
DistributeDitheringError(src, srcCurrentPos, width, height, stride, x, y, 1, 0, 7.0f / 16.0f, errorR, errorG, errorB, errorA);
DistributeDitheringError(src, srcCurrentPos, width, height, stride, x, y, -1, 1, 3.0f / 16.0f, errorR, errorG, errorB, errorA);
DistributeDitheringError(src, srcCurrentPos, width, height, stride, x, y, 0, 1, 5.0f / 16.0f, errorR, errorG, errorB, errorA);
DistributeDitheringError(src, srcCurrentPos, width, height, stride, x, y, 1, 1, 1.0f / 16.0f, errorR, errorG, errorB, errorA);
}
}
}
static void DistributeDitheringError(byte[] src, int srcPos, int width, int height, int stride, int x, int y,
int deltaX, int deltaY, float weight, int errorR, int errorG, int errorB, int errorA)
{
if ((x + deltaX) < width && (y + deltaY) < height)
{
ColorRGBA origPx = ColorRGBA.Read(src, srcPos + 4 * deltaX + stride * deltaY);
ColorRGBA newPx = new ColorRGBA(Utils.Trim8((int)(origPx.Red + errorR * weight)),
Utils.Trim8((int)(origPx.Green + errorG * weight)),
Utils.Trim8((int)(origPx.Blue + errorB * weight)),
Utils.Trim8((int)(origPx.Alpha + errorA * weight)));
newPx.Write(src, srcPos + 4 * deltaX + stride * deltaY);
}
}
/// <summary>
/// Convert an image to grayscale.
/// </summary>
/// <param name="src">The image buffer (RGBA pixels).</param>
/// <param name="srcPos">Initial position on the source buffer.</param>
/// <param name="width">The width of the image.</param>
/// <param name="height">The height of the image.</param>
/// <param name="stride">The distance, in bytes, between rows of the image buffer.</param>
static void GrayscaleImage(byte[] src, int srcPos, int width, int height, int stride)
{
int pos = srcPos;
for (int y = 0; y < height; y++, pos += stride - width * 4)
{
for (int x = 0; x < width; x++, pos += 4)
{
ColorRGBA srcColor = ColorRGBA.Read(src, pos);
ColorRGBA grayscaleColor = ColorRGBA.FromIntensityAlpha(srcColor.Intensity(), srcColor.Alpha);
grayscaleColor.Write(src, pos);
}
}
}
protected override void EncodeTile(byte[] src, int srcPos, int stride, byte[] dst, int dstPos)
{
int srcCurrentPos = srcPos;
for (int ty = 0; ty < TileHeight; ty++, srcCurrentPos += stride - TileWidth * 4)
{
for (int tx = 0; tx < TileWidth; tx++, srcCurrentPos += 4)
{
ColorRGBA color = ColorRGBA.Read(src, srcCurrentPos);
int dstMv = dstPos + ty * 8 + tx * 2;
dst[dstMv + 0] = color.Alpha;
dst[dstMv + 1] = color.Red;
dst[dstMv + 32] = color.Green;
dst[dstMv + 33] = color.Blue;
}
}
}
