/**
* <p>This method traces a line from a po$in the image, in the direction towards another point.
* It begins in a black region, and keeps going until it finds white, then black, then white again.
* It reports the distance from the start to this point.</p>
*
* <p>This is used when figuring out how wide a finder pattern is, when the finder pattern
* may be skewed or rotated.</p>
*/
private function sizeOfBlackWhiteBlackRun($fromX, $fromY, $toX, $toY)
{
// Mild variant of Bresenham's algorithm;
// see http://en.wikipedia.org/wiki/Bresenham's_line_algorithm
$steep = abs($toY - $fromY) > abs($toX - $fromX);
if ($steep) {
$temp = $fromX;
$fromX = $fromY;
$fromY = $temp;
$temp = $toX;
$toX = $toY;
$toY = $temp;
}
$dx = abs($toX - $fromX);
$dy = abs($toY - $fromY);
$error = -$dx / 2;
$xstep = $fromX < $toX ? 1 : -1;
$ystep = $fromY < $toY ? 1 : -1;
// In black pixels, looking for white, first or second time.
$state = 0;
// Loop up until x == toX, but not beyond
$xLimit = $toX + $xstep;
for ($x = $fromX, $y = $fromY; $x != $xLimit; $x += $xstep) {
$realX = $steep ? $y : $x;
$realY = $steep ? $x : $y;
// Does current pixel mean we have moved white to black or vice versa?
// Scanning black in state 0,2 and white in state 1, so if we find the wrong
// color, advance to next state or end if we are in state 2 already
if (($state == 1) == $this->image->get($realX, $realY)) {
if ($state == 2) {
return MathUtils::distance($x, $y, $fromX, $fromY);
}
$state++;
}
$error += $dy;
if ($error > 0) {
if ($y == $toY) {
break;
}
$y += $ystep;
$error -= $dx;
}
}
// Found black-white-black; give the benefit of the doubt that the next pixel outside the image
// is "white" so this last po$at (toX+xStep,toY) is the right ending. This is really a
// small approximation; (toX+xStep,toY+yStep) might be really correct. Ignore this.
if ($state == 2) {
return MathUtils::distance($toX + $xstep, $toY, $fromX, $fromY);
}
// else we didn't find even black-white-black; no estimate is really possible
return NAN;
}
/**
* @param pattern1 first pattern
* @param pattern2 second pattern
* @return distance between two points
*/
public static function distance($pattern1, $pattern2)
{
return MathUtils::distance($pattern1->x, $pattern1->y, $pattern2->x, $pattern2->y);
}
