StemReader.java

package com.xenoage.zong.io.musicxml.in.readers;

import static com.xenoage.utils.collections.CollectionUtils.getFirst;
import static com.xenoage.utils.collections.CollectionUtils.getLast;
import static com.xenoage.zong.core.music.chord.Stem.defaultStem;

import java.util.List;

import lombok.RequiredArgsConstructor;

import com.xenoage.utils.math.VSide;
import com.xenoage.zong.core.Score;
import com.xenoage.zong.core.music.MusicContext;
import com.xenoage.zong.core.music.Pitch;
import com.xenoage.zong.core.music.chord.Chord;
import com.xenoage.zong.core.music.chord.Stem;
import com.xenoage.zong.core.music.chord.StemDirection;
import com.xenoage.zong.musicxml.types.MxlNote;
import com.xenoage.zong.musicxml.types.MxlStem;
import com.xenoage.zong.musicxml.types.attributes.MxlPosition;

/**
 * Reads a {@link Stem} from the given {@link MxlNote} and the context.
 * 
 * @author Andreas Wenger
 */
@RequiredArgsConstructor
public class StemReader {
	
	private final MxlStem mxlStem;
	
	
	/**
	 * Reads and returns the stem of the given chord.
	 * If not available, {@link Stem#defaultStem} is returned.
	 * @param context   the global context
	 * @param chord     the chord, whose notes are already collected
	 * @param staff     the staff index of the current chord
	 */
	public Stem read(Context context, Chord chord, int staff) {
		if (mxlStem == null)
			return defaultStem;
		//direction
		StemDirection direction = readStemDirection();
		//length
		Float length = null;
		MxlPosition yPos = mxlStem.getPosition();
		if (yPos.getDefaultY() != null) {
			//convert position in tenths relative to topmost staff line into
			//a length in interline spaces measured from the outermost chord note on stem side
			float stemEndLinePosition = convertDefaultYToLP(context, yPos.getDefaultY(), staff);
			VSide side = (direction == StemDirection.Up ? VSide.Top : VSide.Bottom);
			length = Math.abs(stemEndLinePosition -
				getOuterNoteLp(context, chord, side, staff)) / 2;
		}
		//create stem
		return new Stem(direction, length);
	}
	
	private StemDirection readStemDirection() {
		switch (mxlStem.getValue()) {
			case None:
				return StemDirection.None;
			case Up:
				return StemDirection.Up;
			case Down:
				return StemDirection.Down;
			case Double:
				return StemDirection.Up; //currently double is not supported
		}
		return null;
	}

	/**
	 * Converts the given default-y position in global tenths (that is always
	 * relative to the topmost staff line) to a line position, using the
	 * musical context from the given staff.
	 */
	private float convertDefaultYToLP(Context context, float defaultY, int staff) {
		Score score = context.getScore();
		float defaultYInMm = defaultY * score.getFormat().getInterlineSpace() / 10;
		float interlineSpace = score.getInterlineSpace(context.getPartStaffIndices().getStart() +
			staff);
		int linesCount = context.getStaffLinesCount(staff);
		return 2 * (linesCount - 1) + 2 * defaultYInMm / interlineSpace;
	}

	/**
	 * Gets the line position of the note at the bottom or top side of the given chord.
	 */
	private static float getOuterNoteLp(Context context, Chord chord, VSide side, int staff) {
		MusicContext mc = context.getMusicContext(staff);
		List<Pitch> pitches = chord.getPitches();
		return mc.getLp(side == VSide.Top ? getLast(pitches) : getFirst(pitches));
	}

}