private static bool TryFindTagCenterCoordinates(TagImage tagImage, int offX, int offY, out int foundCenterX, out int foundCenterY, out int radius)
{
foundCenterX = -1;
foundCenterY = -1;
radius = -1;
if (!TryCalculateDistances(tagImage, tagImage.CenterX + offX, tagImage.CenterY + offY, out int left, out int right, out int down, out int up))
{
return(false);
}
int width = right - left;
int height = up - down;
foundCenterX = (left + width) >> 1;
foundCenterY = (down + height) >> 1;
int diff = width - height;
// Optimized diff = abs(diff), works as long as diff is not int.MinValue, which it is assumed to not be in this case.
diff = (diff + (diff >> 31)) ^ (diff >> 31);
// If the difference is too large, failed to read the image
if (diff > 1)
{
return(false);
}
// Then calculate the radius from given width and height
radius = (width < height ? width : height) >> 1;
return(true);
}
public static byte[] Read(byte[] bytes, int width, int height, uint tolerance, byte[] debugBytes = null)
{
TagImage tagImage = new TagImage()
{
Bytes = bytes,
Width = width,
Height = height,
ColorDifferenceTolerance = tolerance
};
#if DEBUG
if (debugBytes != null)
{
_debugImage = new TagImage()
{
Bytes = debugBytes,
Width = width,
Height = height
};
}
#endif
tagImage.BaseColor = tagImage.ReadColor(tagImage.CenterX, tagImage.CenterY);
int maxIterations = Mathf.Min(width, height) / 32;
if (maxIterations <= 0)
{
return(null);
}
if (!TryFindTagCenterCoordinatesAndRadius(tagImage, maxIterations))
{
return(null);
}
if (!TryFindStartingAngleAndSegmentSize(tagImage))
{
return(null);
}
if (!TryFindLayerSizeAndCount(tagImage))
{
return(null);
}
return(TryReadData(tagImage, out byte[] readBytes) ? readBytes : null);
}
private static bool TryFindTagCenterCoordinatesAndRadius(TagImage tagImage, int maxIterations)
{
// Try finding the tag center iteratively
for (int iteration = 0; iteration < maxIterations; iteration++)
{
// Search center in four pixel steps
int offX = iteration * 5;
int offY = iteration * 5;
// Check if we went past the half of the width of the image
if (offX > tagImage.CenterX)
{
return(false);
}
if (offY > tagImage.CenterY)
{
return(false);
}
// Alternate offset direction between iterations
if (iteration % 2 == 0)
{
offX = -offX;
offY = -offY;
}
if (iteration % 4 == 0)
{
offY = -offY;
}
if (iteration % 3 == 0)
{
offX = -offX;
}
// Try finding the center with the given offset
if (TryFindTagCenterCoordinates(tagImage, offX, offY, out int codeCenterX, out int codeCenterY, out int radius))
{
tagImage.CodeCenterX = codeCenterX;
tagImage.CodeCenterY = codeCenterY;
tagImage.CodeRadius = radius;
return(true);
}
}
return(false);
}
private static bool TryFindStartingAngleAndSegmentSize(TagImage tagImage)
{
double startingAngle = -1;
const double angleStepSize = Math.PI / 360.0 / 2.0;
const int radiusOffset = 2;
double currentAngle = 0.0;
for (int step = 0; currentAngle < Math.PI * 2; step++)
{
currentAngle = angleStepSize * step;
CalculateCoords(tagImage, currentAngle, tagImage.CodeRadius + radiusOffset, out int x, out int y);
_debugImage?.WriteColor(x, y, 0xff0000ff);
if (x < 0 || y < 0 || x > tagImage.Width || y > tagImage.Width)
{
continue;
}
bool hasPixel = tagImage.CheckPixel(x, y);
// Find the first pixel in the notch of the first layer
if (startingAngle < 0 && !hasPixel)
{
startingAngle = currentAngle - angleStepSize;
_debugImage?.WriteColor(x, y, 0xffff00ff);
}
// Find the last pixel in the notch of the first layer
if (startingAngle > 0 && hasPixel)
{
tagImage.CodeStartingAngle = startingAngle;
tagImage.CodeSegmentSize = currentAngle - startingAngle;
_debugImage?.WriteColor(x, y, 0xff00ffff);
return(true);
}
}
return(false);
}
private static bool TryCalculateDistances(TagImage tagImage, int originX, int originY, out int left, out int right, out int down, out int up)
{
left = -1;
right = -1;
down = -1;
up = -1;
int size = tagImage.Width / 2;
uint diff = 0;
for (int i = 1; i < size; i++)
{
int x = originX - i;
int y = originY;
if (x >= 0 && x < tagImage.Width)
{
if (left < 0 && tagImage.CheckPixel(x, y, out diff))
{
left = x + 1;
}
_debugImage?.WriteColor(x, y, diff | 0xff000000);
}
x = originX + i;
if (x >= 0 && x < tagImage.Width)
{
if (right < 0 && tagImage.CheckPixel(x, y, out diff))
{
right = x - 1;
}
_debugImage?.WriteColor(x, y, diff | 0xff000000);
}
x = originX;
y = originY - i;
if (y >= 0 && y < tagImage.Height)
{
if (down < 0 && tagImage.CheckPixel(x, y, out diff))
{
down = y + 1;
}
_debugImage?.WriteColor(x, y, diff | 0xff000000);
}
y = originY + i;
if (y >= 0 && y < tagImage.Height)
{
if (up < 0 && tagImage.CheckPixel(x, y, out diff))
{
up = y - 1;
}
_debugImage?.WriteColor(x, y, diff | 0xff000000);
}
if (left >= 0 && right >= 0 && down >= 0 && up >= 0)
{
return(true);
}
}
return(false);
}
private static void CalculateCoords(TagImage image, double angle, int distance, out int x, out int y)
{
x = (int)Math.Round(Math.Cos(-angle) * distance) + image.CodeCenterX;
y = (int)Math.Round(Math.Sin(-angle) * distance) + image.CodeCenterY;
}
private static bool TryReadData(TagImage tagImage, out byte[] bytes)
{
bytes = null;
int segments = CalculateSegmentCount(tagImage.CodeSegmentSize);
if (segments <= 0)
{
return(false);
}
double halfSegment = tagImage.CodeSegmentSize / 2.0;
int byteIndex = 0;
byte currentBit = 1;
byte currentByte = 0;
byte sizeByte = 0;
for (int layer = 0; layer < tagImage.CodeLayerCount; layer++)
{
for (int segment = 1; segment < segments; segment++)
{
// Calculate coordinates
double angle = tagImage.CodeStartingAngle + segment * tagImage.CodeSegmentSize + halfSegment;
int distance = tagImage.CodeRadius + tagImage.CodeLayerSize + layer * tagImage.CodeLayerSize + tagImage.CodeLayerSize / 2;
CalculateCoords(tagImage, angle, distance, out int x, out int y);
// Read bit
if (tagImage.CheckPixel(x, y))
{
currentByte |= currentBit;
}
// Advance bit and check if there are more bits
currentBit <<= 1;
if (currentBit > 0)
{
continue;
}
// No more bits, handle byte
currentBit = 1;
if (sizeByte == 0)
{
// Size not read yet, use the current byte value as data size and continue reading
sizeByte = currentByte;
currentByte = 0;
bytes = new byte[sizeByte];
continue;
}
if (byteIndex == sizeByte)
{
// We have read all bytes, check hash byte and return
byte hash = CalculateHash(bytes);
return(hash == currentByte);
}
// Push the current byte to the byte array and continue reading
bytes[byteIndex] = currentByte;
currentByte = 0;
byteIndex++;
}
}
return(false);
}
private static bool TryFindLayerSizeAndCount(TagImage tagImage)
{
int layerSize = 0;
int layerCount = 0;
double angle = tagImage.CodeStartingAngle + tagImage.CodeSegmentSize / 2.0;
int startingIndex = tagImage.CodeRadius;
uint dataColor = 0;
int usedWidth = Math.Min(tagImage.CodeCenterX, tagImage.Width / 2);
// Find layer size
for (int i = startingIndex; i < tagImage.Width; i++)
{
CalculateCoords(tagImage, angle, i, out int x, out int y);
if (x < 0 || y < 0 || x > tagImage.Width || y > tagImage.Height)
{
continue;
}
uint color = tagImage.ReadColor(x, y);
uint diff = tagImage.ColorDiff(color);
if (diff < tagImage.ColorDifferenceTolerance)
{
continue;
}
dataColor = color;
layerSize = i - startingIndex - 1;
startingIndex = i;
break;
}
if (layerSize == 0 || layerSize == usedWidth)
{
return(false);
}
// Find size of the tag data block (layer size * layer count, starting from the first data layer)
int dataSize = -1;
for (int i = startingIndex; i < tagImage.Width; i++)
{
CalculateCoords(tagImage, angle, i, out int x, out int y);
if (x < 0 || y < 0 || x > tagImage.Width || y > tagImage.Height)
{
continue;
}
uint color = tagImage.ReadColor(x, y);
uint diff = TagImage.ColorDiff(color, dataColor);
if (diff < tagImage.ColorDifferenceTolerance)
{
continue;
}
dataSize = i - startingIndex - 1;
break;
}
if (dataSize < 0)
{
return(false);
}
layerCount = (int)Math.Round((double)dataSize / (double)layerSize);
tagImage.CodeLayerSize = layerSize;
tagImage.CodeLayerCount = layerCount;
return(true);
}