问题描述
我已经为不同力和角度的弹丸运动编写了以下函数，但它无法正常工作.我哪里错了?我想要类似 Angry Birds 游戏的东西.
I have written the following function for projectile motion of different force and angle, but it doesn't work properly. Where have I gone wrong? I want something like the Angry Birds game.
代码:
public void shootBall(int timeCounter){
int gravity = 4;
double time = timeCounter/40.0;
int velocity = force_value;
double radians = currentangle*Math.PI/180;
ball.setX((int)((ball.getX()+10)*Math.cos(radians) + velocity*Math.cos(radians)*time));
ball.setY((int)((ball.getY()+10)*Math.sin(radians) + velocity*Math.sin(radians)*time - 0.5*gravity*time*time));
updateGame();
}
我想从左下角扔球.
推荐答案
正如评论中所指出的(以及答案 https://stackoverflow.com/a/21785385 ) :为了实现弹丸的真实"弹道轨迹，重要的是要考虑速度 - 以及给定加速度的速度变化(基于在重力上).诚然，我并不完全理解您想通过当前位置更新中的 sin/cos 计算实现什么.但是我这里已经有了一些接近你想要实现的 SSCE，所以我对它进行了一些调整.其中大部分是 q&d-boilerplate 代码，但您可能想查看 Projectile 类以及如何在其 performTimeStep 方法中更新速度和位置.
As pointed out in the comment (and in the answer https://stackoverflow.com/a/21785385 ) : In order to achieve a "realistic" ballistic trajectory for the projectile, it is important to take the velocity into account - as well as the change of velocity for the given acceleration (based on the gravity force). Admittedly, I did not entirely understand what you wanted to achive with the sin/cos computation in your current position update. But I already had some SSCE here that was close to what you want to achieve, so I adapted it a little bit. Most of this is q&d-boilerplate code, but you might want to have a look at the Projectile class and how the velocity and position are updated in its performTimeStep method.
顺便说一句:这种方法有一个很好的优势，它可以很容易地扩展到像风这样的模型:只需使用不同的加速度.例如，不是 (0,-9.81) 而是 (1,-9.81) 来模拟来自左侧的微风.
BTW: This approach has the nice advantage that it can easily be extended to model something like wind: Just use a different acceleration. For example, not (0,-9.81) but (1,-9.81) to simulate a light wind from the left.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.geom.AffineTransform;
import java.awt.geom.Point2D;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;
public class ProjectileShooterTest
{
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable()
{
@Override
public void run()
{
createAndShowGUI();
}
});
}
private static void createAndShowGUI()
{
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(600,600);
final ProjectileShooter projectileShooter =
new ProjectileShooter();
ProjectileShooterPanel projectileShooterPanel =
new ProjectileShooterPanel(projectileShooter);
projectileShooter.setPaintingComponent(projectileShooterPanel);
JPanel controlPanel = new JPanel(new GridLayout(1,0));
controlPanel.add(new JLabel("Angle"));
final JSlider angleSlider = new JSlider(0, 90, 45);
controlPanel.add(angleSlider);
controlPanel.add(new JLabel("Power"));
final JSlider powerSlider = new JSlider(0, 100, 50);
controlPanel.add(powerSlider);
JButton shootButton = new JButton("Shoot");
shootButton.addActionListener(new ActionListener()
{
@Override
public void actionPerformed(ActionEvent e)
{
int angleDeg = angleSlider.getValue();
int power = powerSlider.getValue();
projectileShooter.setAngle(Math.toRadians(angleDeg));
projectileShooter.setPower(power);
projectileShooter.shoot();
}
});
controlPanel.add(shootButton);
f.getContentPane().setLayout(new BorderLayout());
f.getContentPane().add(controlPanel, BorderLayout.NORTH);
f.getContentPane().add(projectileShooterPanel, BorderLayout.CENTER);
f.setVisible(true);
}
}
class ProjectileShooter
{
private double angleRad = Math.toRadians(45);
private double power = 50;
private Projectile projectile;
private JComponent paintingComponent;
void setPaintingComponent(JComponent paintingComponent)
{
this.paintingComponent = paintingComponent;
}
void setAngle(double angleRad)
{
this.angleRad = angleRad;
}
void setPower(double power)
{
this.power = power;
}
void shoot()
{
Thread t = new Thread(new Runnable()
{
@Override
public void run()
{
executeShot();
}
});
t.setDaemon(true);
t.start();
}
private void executeShot()
{
if (projectile != null)
{
return;
}
projectile = new Projectile();
Point2D velocity =
AffineTransform.getRotateInstance(angleRad).
transform(new Point2D.Double(1,0), null);
velocity.setLocation(
velocity.getX() * power * 0.5,
velocity.getY() * power * 0.5);
projectile.setVelocity(velocity);
//System.out.println("Initial "+velocity);
long prevTime = System.nanoTime();
while (projectile.getPosition().getY() >= 0)
{
long currentTime = System.nanoTime();
double dt = 3 * (currentTime - prevTime) / 1e8;
projectile.performTimeStep(dt);
prevTime = currentTime;
paintingComponent.repaint();
try
{
Thread.sleep(10);
}
catch (InterruptedException e)
{
Thread.currentThread().interrupt();
return;
}
}
projectile = null;
paintingComponent.repaint();
}
Projectile getProjectile()
{
return projectile;
}
}
class Projectile
{
private final Point2D ACCELERATION = new Point2D.Double(0, -9.81 * 0.1);
private final Point2D position = new Point2D.Double();
private final Point2D velocity = new Point2D.Double();
public Point2D getPosition()
{
return new Point2D.Double(position.getX(), position.getY());
}
public void setPosition(Point2D point)
{
position.setLocation(point);
}
public void setVelocity(Point2D point)
{
velocity.setLocation(point);
}
void performTimeStep(double dt)
{
scaleAddAssign(velocity, dt, ACCELERATION);
scaleAddAssign(position, dt, velocity);
//System.out.println("Now at "+position+" with "+velocity);
}
private static void scaleAddAssign(
Point2D result, double factor, Point2D addend)
{
double x = result.getX() + factor * addend.getX();
double y = result.getY() + factor * addend.getY();
result.setLocation(x, y);
}
}
class ProjectileShooterPanel extends JPanel
{
private final ProjectileShooter projectileShooter;
public ProjectileShooterPanel(ProjectileShooter projectileShooter)
{
this.projectileShooter = projectileShooter;
}
@Override
protected void paintComponent(Graphics gr)
{
super.paintComponent(gr);
Graphics2D g = (Graphics2D)gr;
Projectile projectile = projectileShooter.getProjectile();
if (projectile != null)
{
g.setColor(Color.RED);
Point2D position = projectile.getPosition();
int x = (int)position.getX();
int y = getHeight() - (int)position.getY();
g.fillOval(x-01, y-10, 20, 20);
}
}
}
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