FFTDrawer/app/src/main/java/com/feemers/android/fftdrawer/BarChart.java

package com.feemers.android.fftdrawer;

import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;

import java.util.ArrayList;

public class BarChart implements Animation {

    private final int length;
    private ArrayList<Bar> bars = null;

    private Paint paint;
    private int backgroundColor;

    public BarChart(int length){
        this.length = length;
        bars = new ArrayList<>();

        paint = new Paint();
        paint.setAntiAlias(true);
        backgroundColor = Color.rgb(0,0,0);
    }

    public void newValues(double[] values){
        bars.clear();
        for(int i = 0; i < length; i++){
            float tmp = (float) values[i];
            bars.add(new Bar(tmp, i));
        }
    }

    @Override
    public void Draw(Canvas canvas) {
        paint.setStyle(Paint.Style.FILL);
        canvas.drawColor(backgroundColor);
        // find max
        float maxValue = 0;
        for(Bar b : bars){
            maxValue = maxValue >= b.getValue() ? maxValue : b.getValue();
        }
        for(Bar b : bars){
            paint.setColor(b.getColor());
            float width = canvas.getWidth();
            float heigth = canvas.getHeight();
            float widthOfBar = width / length;

            float left= b.getHarmonics() * widthOfBar;
            float top = heigth - heigth * b.getValue() / maxValue;
            float rigth = (b.getHarmonics()+1) * widthOfBar;
            float buttom = heigth;

            canvas.drawRect(left, top, rigth ,buttom, paint);
        }
    }

    @Override
    public void SetBackgroundColor(int c) {
        backgroundColor = c;
    }
}