RadarView.java

public class RadarView extends View {

    private final String LOG = "RadarView";
    private final int POINT_ARRAY_SIZE = 25;
    float alpha = 0;
    Point latestPoint[] = new Point[POINT_ARRAY_SIZE];
    Paint latestPaint[] = new Paint[POINT_ARRAY_SIZE];
    android.os.Handler mHandler = new android.os.Handler();
    private int fps = 100;
    Runnable mTick = new Runnable() {
        @Override
        public void run() {
            invalidate();
            mHandler.postDelayed(this, 1000 / fps);
        }
    };
    private boolean showCircles = true;

    public RadarView(Context context) {
        this(context, null);
    }


    public RadarView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public RadarView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        Paint localPaint = new Paint();
        localPaint.setColor(getResources().getColor(R.color.colorPrimary));
        localPaint.setAntiAlias(true);
        localPaint.setStyle(Paint.Style.STROKE);
        localPaint.setStrokeWidth(1.0F);
        localPaint.setAlpha(0);

        int alpha_step = 255 / POINT_ARRAY_SIZE;
        for (int i = 0; i < latestPaint.length; i++) {
            latestPaint[i] = new Paint(localPaint);
            latestPaint[i].setAlpha(255 - (i * alpha_step));
        }
    }

    public void startAnimation() {
        mHandler.removeCallbacks(mTick);
        mHandler.post(mTick);
    }

    public void stopAnimation() {
        mHandler.removeCallbacks(mTick);
    }

    public int getFrameRate() {
        return this.fps;
    }

    public void setFrameRate(int fps) {
        this.fps = fps;
    }

    ;

    public void setShowCircles(boolean showCircles) {
        this.showCircles = showCircles;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);


        int width = getWidth();
        int height = getHeight();

        int r = Math.min(width, height);


        //canvas.drawRect(0, 0, getWidth(), getHeight(), localPaint);

        int i = r / 2;
        int j = i - 1;
        Paint localPaint = latestPaint[0]; // GREEN

        if (showCircles) {
            canvas.drawCircle(i, i, j, localPaint);
            canvas.drawCircle(i, i, j, localPaint);
            canvas.drawCircle(i, i, j * 3 / 4, localPaint);
            canvas.drawCircle(i, i, j >> 1, localPaint);
            canvas.drawCircle(i, i, j >> 2, localPaint);
        }

        alpha -= 0.5;
        if (alpha < -360) alpha = 0;
        double angle = Math.toRadians(alpha);
        int offsetX = (int) (i + (float) (i * Math.cos(angle)));
        int offsetY = (int) (i - (float) (i * Math.sin(angle)));

        latestPoint[0] = new Point(offsetX, offsetY);

        for (int x = POINT_ARRAY_SIZE - 1; x > 0; x--) {
            latestPoint[x] = latestPoint[x - 1];
        }


        int lines = 0;
        for (int x = 0; x < POINT_ARRAY_SIZE; x++) {
            Point point = latestPoint[x];
            if (point != null) {
                canvas.drawLine(i, i, point.x, point.y, latestPaint[x]);
            }
        }


        lines = 0;
        for (Point p : latestPoint) if (p != null) lines++;

        boolean debug = false;
        if (debug) {
            StringBuilder sb = new StringBuilder(" >> ");
            for (Point p : latestPoint) {
                if (p != null) sb.append(" (" + p.x + "x" + p.y + ")");
            }

            Log.d(LOG, sb.toString());
            //  " - R:" + r + ", i=" + i +
            //  " - Size: " + width + "x" + height +
            //  " - Angle: " + angle +
            //  " - Offset: " + offsetX + "," + offsetY);
        }

    }

}