If you know...
- The position of the weapon
- It's angle of direction
- The length (from it's centre point to it's end point)
Then you can simply apply a "point on circle" approach to the problem, for example...
The blue line is the weapon, the red line is the projection of the projectile path. Oddly enough, it's calculating both the start and end point the projectile should follow
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.Timer;
public class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
enum WeaponInput {
LEFT, RIGHT, NONE
}
public class TestPane extends JPanel {
private static final double MIN_WEAPON_ANGLE = -85;
private static final double MAX_WEAPON_ANGLE = 85;
private double angleOfWeapon = 0;
private double weaponAngleDelta = 1;
private WeaponInput weaponInput = WeaponInput.NONE;
private Timer timer;
public TestPane() {
setBackground(Color.BLACK);
InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
ActionMap am = getActionMap();
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, false), "Pressed.weaponMoveLeft");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, false), "Pressed.weaponMoveRight");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, true), "Pressed.weaponReleasedLeft");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, true), "Pressed.weaponReleasedRight");
WeaponMovementAction.WeaponObserver weaponObserver = new WeaponMovementAction.WeaponObserver() {
@Override
public void weaponDidMove(WeaponInput weaponInput) {
TestPane.this.weaponInput = weaponInput;
}
};
am.put("Pressed.weaponMoveLeft", new WeaponMovementAction(WeaponInput.LEFT, weaponObserver));
am.put("Pressed.weaponMoveRight", new WeaponMovementAction(WeaponInput.RIGHT, weaponObserver));
am.put("Pressed.weaponReleasedLeft", new WeaponMovementAction(WeaponInput.NONE, weaponObserver));
am.put("Pressed.weaponReleasedRight", new WeaponMovementAction(WeaponInput.NONE, weaponObserver));
timer = new Timer(5, new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
switch (weaponInput) {
case LEFT:
angleOfWeapon -= weaponAngleDelta;
break;
case RIGHT:
angleOfWeapon += weaponAngleDelta;
break;
}
if (angleOfWeapon < MIN_WEAPON_ANGLE) {
angleOfWeapon = MIN_WEAPON_ANGLE;
} else if (angleOfWeapon > MAX_WEAPON_ANGLE) {
angleOfWeapon = MAX_WEAPON_ANGLE;
}
repaint();
}
});
timer.start();
}
protected Point2D getPointOnCircle(double degress, double radius) {
double rads = Math.toRadians(degress - 90); // 0 becomes the top
// Calculate the outter point of the line
double xPosy = Math.cos(rads) * radius;
double yPosy = Math.sin(rads) * radius;
return new Point2D.Double(xPosy, yPosy);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(400, 400);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
int centerX = getWidth() / 2;
int centerY = getHeight() / 2;
g2d.setColor(Color.WHITE);
g2d.drawRect(centerX - 20, centerY - 20, 40, 40);
g2d.setColor(Color.RED);
g2d.translate(centerX, centerY - 20);
// Projection of projectile
g2d.setColor(Color.BLUE);
Point2D endOfWeaponPoint = getPointOnCircle(angleOfWeapon, 20);
g2d.draw(new Line2D.Double(new Point2D.Double(0, 0), endOfWeaponPoint));
// Weapon direction
int radius = Math.max(getWidth(), getHeight());
g2d.setColor(Color.RED);
Point2D poc = getPointOnCircle(angleOfWeapon, radius);
g2d.draw(new Line2D.Double(endOfWeaponPoint, poc));
g2d.dispose();
}
}
public class WeaponMovementAction extends AbstractAction {
public interface WeaponObserver {
public void weaponDidMove(WeaponInput weaponInput);
}
private WeaponInput weaponInput;
private WeaponObserver observer;
public WeaponMovementAction(WeaponInput weaponInput, WeaponObserver observer) {
this.weaponInput = weaponInput;
this.observer = observer;
}
@Override
public void actionPerformed(ActionEvent e) {
getObserver().weaponDidMove(getWeaponInput());
}
public WeaponInput getWeaponInput() {
return weaponInput;
}
public WeaponObserver getObserver() {
return observer;
}
}
}
