How can I ensure the missile stays on the screen when non-spacebar keys are pressed? - processing

Question

I need to write a Processing program so that "When the user presses the space key a missile is fired from the front of the ship and moves rightwards until leaving the screen. The user can't fire another missile until the first is off the screen."
What I have written doesn't allow the missile to stay on the screen if other keys are pressed. I have tried adding the function under void keyPressed() with boolean true/false statements which only stopped the whole program from working.
How can I make sure it stays on the page? Also, how can I make sure the player can't shoot another missile until their previous one moves off the screen?
This is the code I have:
//global
int ship_y;
int angle;
int missileX;
void setup(){
size(500, 500);
ship_y = 10;
missileX = 55;
}
void draw(){
background(175);
fill(50);
rectMode(CENTER);
rect(30, ship_y, 50, 25);
//missile moves rightwards after spacebar is pressed
if (key == ' '){
circle(missileX, ship_y, 25);
missileX = missileX + 1;
}
}
//ship moves down when 's' is pressed and up when 'w' is pressed
void keyPressed(){
if (key == 's'){
ship_y = ship_y + 2;
}
if (key == 'w'){
ship_y = ship_y - 2;
}
}

Answer 1

Code within the draw() function runs every frame.
So every frame, you're clearing the background, drawing the ship, and drawing the missile. Good.
But.
You put the missile drawing code inside this if statement:
if (key == ' '){
that only draws the missile if the most recent key pressed was space. So as soon as you you press a different key, key is no longer equal to space and your missile doesn't get drawn.
One way to fix it would be to create a variable to indicate whether or not the missile was fired, and use that to determine whether or not to draw the missile (instead of checking the key variable).
Like this:
if (missileFired == true){
circle(missileX, ship_y, 25);
missileX = missileX + 1;
}
Code inside the keyPressed() function only runs once each time a key is pressed. This would be a better place to detect when the spacebar is pressed and turn on the missileFired flag:
void keyPressed(){
// code for other keypresses...
if(key == ' '){
missileFired = true;
}
}
To detect when the missile goes off screen, you'll just need to check whether missileX is greater than the width of the window. draw() would be a good place for that, since you probably want to check for it every time the missile moves.
When missileX gets larger than the window width, you can reset missileFired to false so a new missile can be fired. You'll also need to reset missileX to its original position so it originates from the ship position.