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Tank illustrates some slightly fancy use of pinning, some calculations
to determine rotation, and the onKeyRelease() callback method.
Up and down arrows aim the cannon. Hold down the space key to increase firing power, and release to fire. R to reset and start over. |
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Tank.java
import ucigame.*;
public class Tank extends Ucigame
{
Sprite platform;
Sprite gun;
Sprite shell;
Sprite movingShell;
int angle = 0;
double pullback = 0.0;
boolean spacePressed = false;
boolean shellBeingFired = false;
boolean waitForReset = false;
double shellX, shellY;
double velocityX, velocityY;
int framesInFlight = 0;
public void setup()
{
window.size(250, 250);
window.title("Tank");
framerate(30);
Image bkg = getImage("images/tank-background.png");
canvas.background(bkg);
platform = makeSprite(getImage("images/tank-platform.png", 255, 255, 0));
gun = makeSprite(getImage("images/tank-gun.png"));
shell = makeSprite(getImage("images/tank-shell.png", 255, 255, 0));
movingShell = makeSprite(getImage("images/tank-shell.png", 255, 255, 0));
movingShell.hide();
platform.position(5, 183);
platform.pin(gun, 22, 12);
gun.pin(shell, 14, 0);
}
public void draw()
{
canvas.clear();
if (shellBeingFired)
{
updateShellPosition();
if (shellY > canvas.height() - 10)
{
shellBeingFired = false;
waitForReset = true;
}
}
gun.rotate(angle, -1, 3); // (-1, 3) is relative to the gun's ulh corner
shell.position(-pullback, 0); // relative to the gun
platform.draw();
movingShell.draw(); // only if not hidden, if shellBeingFired = true;
}
// Any resemblance to actual physics is purely coincidental.
public void updateShellPosition()
{
shellX = shellX + velocityX;
shellY = shellY + velocityY;
movingShell.position(shellX, shellY);
velocityX = velocityX * 0.98; // drag
framesInFlight = framesInFlight + 1;
velocityY = velocityY + framesInFlight * 0.03; // gravity
}
public void onKeyPress()
{
if (keyboard.isDown(keyboard.R)) // reset
{
pullback = angle = framesInFlight = 0;
spacePressed = shellBeingFired = waitForReset = false;
movingShell.hide();
shell.show();
return;
}
if (shellBeingFired || waitForReset)
return;
if (keyboard.isDown(keyboard.UP, keyboard.LEFT))
{
if (angle > -135)
angle = angle - 1;
}
if (keyboard.isDown(keyboard.DOWN, keyboard.RIGHT))
{
if (angle < 0)
angle = angle + 1;
}
if (keyboard.isDown(keyboard.SPACE))
{
spacePressed = true;
if (pullback < 15)
pullback = pullback + 0.2;
}
}
// Fire on space key up.
public void onKeyRelease()
{
if (spacePressed && !keyboard.isDown(keyboard.SPACE))
{
shellBeingFired = true;
spacePressed = false;
double angleInRadians = -angle * Math.PI / 180.0;
shellX = 23 + Math.cos(angleInRadians) * 24;
shellY = 195 - Math.sin(angleInRadians) * 24;
velocityX = Math.cos(angleInRadians) * pullback;
velocityY = -Math.sin(angleInRadians) * pullback;
shell.hide();
movingShell.show();
movingShell.position(shellX, shellY);
}
}
}
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