How to draw a graph of a mathematical function, on an Android canvas

Question

我如何在 Android 應用程序的Canvas上繪制 function 的圖形（例如， y = x^2或 y = (x +1)/(2*x +3)）？

Answer 1

Here you have an example code;D（繪制 f(x)=x^3 函數）

繪制 function 的示例線程。

public class MainThread extends Thread {
private static final String TAG = MainThread.class.getSimpleName();
private SurfaceHolder surfaceHolder;
private MainGamePanel gamePanel;
private Paint paintRed;
private Paint paintBlue;
private boolean running;

public void setRunning(boolean running) {
    this.running = running;
}

public MainThread(SurfaceHolder surfaceHolder, MainGamePanel gamePanel) {
    super();

    this.paintRed = new Paint();
    this.paintRed.setColor(Color.RED);
    this.paintRed.setStrokeWidth(1);

    this.paintBlue = new Paint();
    this.paintBlue.setColor(Color.BLUE);
    this.paintBlue.setStrokeWidth(1);

    this.surfaceHolder = surfaceHolder;
    this.gamePanel = gamePanel;
}

class MeasuredAxis {
    public static final int X_GAP = 1;
    public static final int Y_GAP = 1;

    int _realHeight;
    int _realWidth;

    public MeasuredAxis(int width, int height) {
        _realWidth = width;
        _realHeight = height;
    }

    public int getXAxisNegLimit() {
        return (_realWidth / 2)*(-1);
    }

    public int getXAxisLimit() {
        return (_realWidth / 2);
    }

    public float getXMeasured(int x) {
        return ((_realWidth / 2) + x);
    }

    public float getYMeasured(float y) {
        return ((_realHeight / 2) - y);
    }
}


private float function(float x) {
    return new Double(Math.pow(x, 3)).floatValue();
}

@Override
public void run() {
    long fps = 0L;
    Log.d(TAG, "Starting game loop");
    Canvas canvas = surfaceHolder.lockCanvas();

    MeasuredAxis measured = new MeasuredAxis(canvas.getWidth(), canvas.getHeight());

    synchronized (canvas) {
        int x = measured.getXAxisNegLimit();
        //from -x to +x evaluate and plot the function
        while (x++ < measured.getXAxisLimit()) {
            canvas.drawLine(
                    measured.getXMeasured(x),
                    measured.getYMeasured(function(x)),
                    measured.getXMeasured(x+MeasuredAxis.X_GAP),
                    measured.getYMeasured(function(x+MeasuredAxis.Y_GAP)),
                    paintRed);
        }
        canvas.save();
        canvas.translate(0, 0);
        canvas.scale(canvas.getWidth(), canvas.getHeight());
        canvas.restore();

    }
    surfaceHolder.unlockCanvasAndPost(canvas);

}
    }

繪制 function 的示例表面視圖。

    public class MainGamePanel extends SurfaceView implements
    SurfaceHolder.Callback {
private MainThread thread;

public MainGamePanel(Context context) {
    super(context);
    getHolder().addCallback(this);
    // create the game loop thread
    thread = new MainThread(getHolder(), this);
    setFocusable(true);
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
        int height) {
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
    thread.setRunning(true);
    thread.start();
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
    boolean retry = true;
    while (retry) {
        try {
            thread.join();
            retry = false;
        } catch (InterruptedException e) {
            // try again shutting down the thread
        }
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    return super.onTouchEvent(event);
}

@Override
protected void onDraw(Canvas canvas) {


}
    }

和一個示例活動

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
    setContentView(new MainGamePanel(this));
}
}

希望這對你有幫助！