Method Increment

src/tilearea.cpp:365–399

* Advance the internal state to the next potential tile. * The tile may be outside the map though. */

 * The tile may be outside the map though.
 */
void SpiralTileIterator::Increment()
{
	assert(!this->IsEnd());

	/* Special value for first tile in areas with odd diameter */
	if (this->dir == INVALID_DIAGDIR) {
		const auto west = TileIndexDiffCByDir(DIR_W);
		this->x += west.x;
		this->y += west.y;
		this->dir = DIAGDIR_BEGIN;
		this->InitPosition();
		return;
	}

	/* Step to the next 'neighbour' in the circular line */
	const auto diff = TileIndexDiffCByDiagDir(this->dir);
	this->x += diff.x;
	this->y += diff.y;
	--this->position;
	if (this->position > 0) return;

	/* Corner reached, switch direction */
	++this->dir;

	if (this->dir == DIAGDIR_END) {
		/* Jump to next circle */
		const auto west = TileIndexDiffCByDir(DIR_W);
		this->x += west.x;
		this->y += west.y;
		++this->cur_radius;
		this->dir = DIAGDIR_BEGIN;
	}

	this->InitPosition();
}