Top-Down RPG Shooter — Part 2 — Player Movement

Welcome back to the second part of my “Top-Down RPG Shooter” flash game tutorial. In the last part, we set up a new project and linked it to an external Document Class, and we added the Player to the stage. In this tutorial, we’re going to program keyboard controls to move the player.

Step 1: KeyObject.as

We are going to make use of a really great open-source class called “KeyObject.as“. This class was written by a talented developer named senocular. It provides a really simple but powerful way to check which keyboard keys are pressed.

Copy and paste this class into a new .as actionscript file, and save it as “KeyObject.as” in the same folder as your main project:

package {

	import flash.display.Stage;
	import flash.events.KeyboardEvent;
	import flash.ui.Keyboard;
	import flash.utils.Proxy;
	import flash.utils.flash_proxy;

	/**
	 * The KeyObject class recreates functionality of
	 * Key.isDown of ActionScript 1 and 2
	 *
	 * Usage:
	 * var key:KeyObject = new KeyObject(stage);
	 * if (key.isDown(key.LEFT)) { ... }
	 */
	dynamic public class KeyObject extends Proxy {

		private static var stage:Stage;
		private static var keysDown:Object;

		public function KeyObject(stage:Stage) {
			construct(stage);
		}

		public function construct(stage:Stage):void {
			KeyObject.stage = stage;
			keysDown = new Object();
			stage.addEventListener(KeyboardEvent.KEY_DOWN, keyPressed);
			stage.addEventListener(KeyboardEvent.KEY_UP, keyReleased);
		}

		flash_proxy override function getProperty(name:*):* {
			return (name in Keyboard) ? Keyboard[name] : -1;
		}

		public function isDown(keyCode:uint):Boolean {
			return Boolean(keyCode in keysDown);
		}

		public function deconstruct():void {
			stage.removeEventListener(KeyboardEvent.KEY_DOWN, keyPressed);
			stage.removeEventListener(KeyboardEvent.KEY_UP, keyReleased);
			keysDown = new Object();
			KeyObject.stage = null;
		}

		private function keyPressed(evt:KeyboardEvent):void {
			keysDown[evt.keyCode] = true;
		}

		private function keyReleased(evt:KeyboardEvent):void {
			delete keysDown[evt.keyCode];
		}
	}
}

How do we use this class? Basically, we’re going to create an instance of it called “key” in our Player class (or wherever we need to access the keyboard controls). Then in that class, we can check the Boolean value of the keyObject’s isDown() function for specific keys. We can refer to keys by their unique keyCode. For example, if key.isDown(65) returns true, it means that the “A” keyboard key is currently being pressed.

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Sidescrolling Platformer – Part 13 – Enemy Interactivity

As I announced in the last post, I am extremely busy right now. Luckily for you, a member of the community has already stepped up and written a Part 13 for this side scrolling tutorial! In this tutorial, you’ll learn to create “bumper” objects for your enemies to interact with, which will let them patrol back and forth. You’ll also look for collisions between the player and the enemies, so you can take damage in your game. Cool!

I’ll hand it over now to the newest guest writer around here, Ed Nordmeyer (thanks, Ed!)

Ben covered creating enemies and making them disappear when they’re shot in lesson 12, so in lucky lesson 13, in this guest tutorial, I’ve picked up where the last lesson left off in the side scrolling platform game.

This will cover making the enemies move, how to block them in so they’ll patrol in a simple side-to-side motion, and have them interact with your player if they touch you. Following in Ben’s footsteps, if I had to choose between making the code readable or making the code ultra efficient and take up the least amount of lines, I tried to make the code as easy as possible to understand.

Creating the Bumper class

If you’ve followed the tutorial steps so far, you’ll find that creating the bumper class is very, very similar to the other classes made so far. For the artwork, I just made a square that was about a 25×25 pixels in size. I created this block on the background layer outside of what the player screen shows when you’re running the game. We’ll go back and made the blocks transparent later, but for now I’d recommend making them easy to see to help placing them on the screen from our code.

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Sidescrolling Platformer — Part 12 — Basic Enemies

Welcome back to the side scrolling tutorial series. In this session, we will be adding (very) basic enemies to the game, which you can shoot and destroy with the bullets we created previously. This will create a lot of possibilities for what you can do with your game. In later tutorials we will add a scoring system and more advanced A.I. (artificial intelligence) to the enemies, but for now let’s focus on: creating the Enemy class, adding a few enemies to the game map, and destroying them when they are hit by a bullet.

Creating the Enemy Class

Creating the Enemy class is very similar to creating the Bullet class. If you just read Part 10 and Part 11, most of this step will look the same as when we made the Bullet class and symbol.

First, we need art. We need to create a Movie Clip object to represent the enemy on the stage. Feel free to decorate your enemy however you choose — it could be a random, inanimate object, a crazy monster, or anywhere in between.

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Sidescrolling Platformer — Part 11 — Fixing the bullets

Although we did get some functional bullets last time by using the Bullet class, we still need to make some major improvements. First of all, the bullets are added directly to the stage and have no idea about the scrollX and scrollY variables, so they don’t react when the player moves left, right, up, or down. Also, the bullets move at a sluggish pace — if they did react to the player’s movements, you could practically outrun them. Finally, they are never actually removed from the stage, so we waste precious memory that slows down the game. Imagine that we fired 1,000,000 bullets. The game would still be keeping track of all of them, constantly updating their positions, even if they are no longer on the stage. There’s some more code we can add to the bullets to handle all of this, and we are going to implement it in this tutorial.

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Sidescrolling Platformer — Part 10 — Shooting

Welcome back to the flash game tutorial: how to make a side scrolling platformer game in actionscript 3. I can’t believe we’re already up to part ten! As you can probably tell from the title, this tutorial part will exclusively feature shooting. Not all platformer games require this feature, but I’ve had a bunch of requests for this tutorial — probably because side scrolling shooters are an amazing game genre (for example, the classic Metroid games). We don’t have anything yet for our bullets to interact with, but don’t worry — next tutorial we will add the enemies. For now, let’s just focus on getting our hero to shoot.

Here is a preliminary demo of what we’ll be creating. Use the space bar to fire.

An External Actionscript File

…I knew this moment would arrive eventually… the moment when — *gasp* — we finally need to use a custom class and an external actionscript file. If you’ve never programmed anything with Object Oriented Programming before, and you’ve never created an external .as file, this might seem intimidating. Or perhaps you have no idea what I’m talking about. No matter where you stand right now, I hope that by the end of this tutorial you will have a solid idea of what external classes are, why we use them, and how to create a Class for the bullets. In future tutorials we will go into more depth on the topic.

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Sidescrolling Platformer — Part 9 — Animated Player Movements

All great platformers have animated heroes. Even Super Mario, which was released in 1985, used several animations for the player. Why? Because it would look completely unrealistic if Mario just stood frozen in one animation while he runs and jumps around the level. So it makes sense that we should add animations to our player. This will add yet another step of realism to the game.

Try running, jumping, or standing still. See how the player’s animation state reacts:

My art could definitely be improved, but I’ll demonstrate how to create these 3 animations for simplicity’s sake.

The Structure

The most important aspect of giving any game element multiple animation states, is to make sure you structure it correctly. When I first started programming, I tried to put all of the animations on a single timeline, and the resulting structure was too cluttered and complicated that it was difficult to make things work the way I wanted them to. So now I’m sharing with you a simpler method.

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Sidescrolling Platformer — Part 8 — Multiple Levels

Here’s the post you’ve all been waiting for… how to connect multiple levels in your platformer!

Try out this demo. Press the down arrow key upon opening the door to warp to the next level:

After adding the door and key last time, the next step is to make the door lead to the next level. “How?”, you might ask… just read on to see the magic unfold.

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