LogTickMarkCalculator.java

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package plotter;

import java.util.ArrayList;
import java.util.List;



/**
 * Implementation of {@link TickMarkCalculator} for a logarithmic axis.
 * @author Adam Crume
 */
public class LogTickMarkCalculator implements TickMarkCalculator {
	// TODO: Make the ticks work at different scales
	@Override
	public double[][] calculateTickMarks(Axis axis) {
		double start = axis.getStart();
		double end = axis.getEnd();
		double min = start;
		double max = end;
		if(min > max) {
			double tmp = max;
			max = min;
			min = tmp;
		}
		double diff = max - min;

		// d should be diff scaled to between 1 and 10
		double d = diff / Math.pow(10, Math.floor(Math.log10(diff)));
		double spacing = diff / d;

		double[] minorVals;
		double[] majorVals;

		double startCount = Math.ceil(min / spacing);
		double endCount = Math.floor(max / spacing);
		majorVals = new double[(int)(endCount - startCount) + 1];
		double value = Math.ceil(min / spacing) * spacing;
		for(int i = 0; i < majorVals.length; i++) {
			majorVals[i] = value;
			value += spacing;
		}

		// TODO: Make the calculation for minor ticks efficient
		double base = Math.floor(min / spacing) * spacing;
		List<Double> mins = new ArrayList<Double>();
		while(base <= max) {
			for(int i = 1; i < 10; i++) {
				value = base + Math.log10(i);
				if(value >= min && value <= max) {
					mins.add(value);
				}
			}
			base++;
		}

		minorVals = new double[mins.size()];
		for(int i = 0; i < minorVals.length; i++) {
			minorVals[i] = mins.get(i);
		}

		return new double[][] {majorVals, minorVals};
	}
}