Последовательность Фибоначчи

Учёные утверждают, что семена подсолнуха растут в последовательности Фибоначчи. Википедия вам в помощь.

Пример для визуального просмотра последовательности. Без объяснений.

Компонент

package ru.alexanderklimov.testapplication;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.RectF;


public class SunflowerView extends View {

    public static final Paint sPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    private static int SEED_RADIUS;
    private static int SCALE_FACTOR;
    public static final double TAU = Math.PI * 2;
    public static final double PHI = (Math.sqrt(5) + 1) / 2;
    private int percent, maxSeeds;
    private int xc;
    private int yc;

    public SunflowerView(Context context, AttributeSet attrs) {
        super(context, attrs);
        sPaint.setColor(0xFFF87306);
        sPaint.setStyle(Style.FILL_AND_STROKE);
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right,
                            int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        onLayoutChange();
    }

    void onLayoutChange() {
        int height = this.getHeight();
        int width = this.getWidth();
        SEED_RADIUS = 5;
        SCALE_FACTOR = 7;
        int maxR = Math.min(height, width) / 2;
        int range = (maxR - SEED_RADIUS) / SCALE_FACTOR;
        maxSeeds = range * range;
        Log.i(VIEW_LOG_TAG, "max " + maxSeeds);
        xc = width / 2;
        yc = height / 2;
    }

    /**
     * Draw the complete figure for the current number of seeds
     */
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        int numSeeds = maxSeeds * this.percent / 100;
        for (int i = 0; i < numSeeds; i++) {
            double theta = i * TAU / PHI;
            double r = Math.sqrt(i) * SCALE_FACTOR;
            int x = (int) Math.round(xc + r * Math.cos(theta));
            int y = (int) Math.round(yc - r * Math.sin(theta));
            drawSeed(x, y, canvas);
        }
    }

    void setPercent(int percent) {
        this.percent = percent;
    }

    /**
     * Draw a small circle representing a seed centered at (x,y)
     *
     * @param x      Center of the seed head
     * @param y      Center of the seed head
     * @param canvas Canvas
     */
    private void drawSeed(int x, int y, Canvas canvas) {
        int sr = SEED_RADIUS;
        canvas.drawArc(new RectF(x - sr, y - sr, x + sr, y + sr), 0, 360, false, sPaint);
    }
}

Разметка

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical">

    <SeekBar
        android:id="@+id/seekBar"
        android:layout_height="wrap_content"
        android:layout_width="fill_parent"
        android:layout_gravity="center_horizontal" />

    <ru.alexanderklimov.testapplication.SunflowerView
        android:id="@+id/sunflowerView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

Активность.

package ru.alexanderklimov.testapplication;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.SeekBar;

public class MainActivity extends ActionBarActivity implements
        SeekBar.OnSeekBarChangeListener {

    private SunflowerView mSunflowerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        mSunflowerView = (SunflowerView) findViewById(R.id.sunflowerView);

        SeekBar seekBar = (SeekBar) findViewById(R.id.seekBar);
        seekBar.setOnSeekBarChangeListener(this);
        seekBar.setMax(100);
    }

    @Override
    public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
        mSunflowerView.setPercent(progress);
        // force redraw
        mSunflowerView.postInvalidate();
    }

    @Override
    public void onStartTrackingTouch(SeekBar seekBar) {
    }

    @Override
    public void onStopTrackingTouch(SeekBar seekBar) {
    }
}

идея

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