Writing a game in javascript

When it comes to animating and managing a canvas there are a few more hoops to jump through than when you're animating a typical dom node, mostly because you can't really reference the created canvas contents after you've rendered them. To solve this we're going to wind up storing everything within a central state; with individual entities players, enemies, etc. Then, when it's time to re-render, we'll call each entities render method which will use the data within their states to render the entity correctly.

Since with a canvas we need to clear objects out before re-rendering them in a different position, we're going to be re-rendering the entire canvas every frame. To accomplish this we're going to need a loop, which being JavaScript there are millions of ways to do that. Let's take a look at our primary options:. Our first option, using setTimeout or setInterval would be much easier and readable for the most part , but it's incredibly inefficient.

The second option, while being way more complex, is miles more efficient due to the browser being able to optimize animations during repaint cycles.

Let's start by scaffolding out the modules that we'll be needing for our main loop. The main loop will have three parts:. These modules will need to access some constants that we will be setting in our global game module, so we're going to create a new constants property along with an empty state within our main game module first.

In addition to our original props for the width and height, we've also added a target frame rate prop and a flag for whether or not to render the current FPS; the latter being totally optional both in implementation and use. Now that we're storing all of this inside of a handy dandy exposed object, we can start on our new modules.

Since these are all integral to the functioning of our game, we can count these modules as core modules which we'll instantiate from our main game module. Since the update and rendering method are fairly simple and straight forward for now , so let's start with those. Since we're just scaffolding out our loop and currently have no actual functionality, our update method is going to be really boring.

Eventually it will take the games state object, determine changes in, update it, then return it. We'll just pretend we're doing fancy stuff for now though. Like I said, nothing super crazy going on. We're injecting the global scope 8 , then creating a new object based off of the global state 10 , iterating through entities in the global state 13 , firing the update method for each active entity 16 - 22 , then returning it One interesting thing you may have noticed is that I'm expecting a scope parameter to be passed in first, then I'm returning another function that is actually doing all of the work.

You'll see this in the render method as well, and it's more of a personal preference more than anything.

An alternative would be to remove the returned function, move it's contents into the main gameUpdate function, and instead of injecting the scope we'd tap into the global window. Since I want to avoid hard coding these references in, I'm just injecting the scope as a parameter. The render module is a little more busy than our update one, but it's nothing too crazy yet.

We're going to move our dummy text from the main game module into this one, add our FPS rendering logic, then write a quick little loop to iterate through potential active entities. Like the update module we're injecting the games context 10 , then we're clearing the canvas 17 , rendering our dummy content and setting it up to show the FPS in the top right corner of the canvas if the showFps flag is set The only fanciness occurring here is between lines 31 and 38, where we are iterating through all active entities with a simple for We'll be returning to this module in a little bit to change the text we're writing in place of the actual frame rate, but for now it's completed.

Now it's time for us to move onto our mythical loop, which will by far be the most complex portion of code we've written yet. As I mentioned earlier, we're going to be using requestAnimationFrame to handle our loop, as recommended by MDN and based off of information from Paul Irish , coupled together with some frame rate throttling based on some terrific stack overflow answers.

I know that's a lot to swallow, so we'll tackle this one one by one. Let's start with the loop itself, then we'll jump into the frame rate throttling. By itself the loop isn't too terrifying at all, and if you've checked out the MDN docs on the anatomy of a web game it should be very familiar; we're just creating a callback and passing it into window. I realize this isn't the most elegant way to fire off the update and render methods, but my reasoning is to have the update and render modules instantiated and exposed globally if, for whatever reason, they need to be triggered manually.

An alternative to this would be to require the modules within the game loop module, and instantiate them with the injected context. Next, we'll start with our frame rate throttling. There's quite a lot to this, so I'll try to break it down as best as I can. First we need to set up our variables for calculating the frame rate.

Whoa, that's a lot of variables. Keeping the code comments in mind, there's one thing I would like to explain which is the cycles object. Note: This series of articles can be used as material for hands-on game development workshops.

You can also make use of the Gamedev Canvas Content Kit based on this tutorial if you want to give a talk about game development in general. Ok, let's get started! If you want more complicated physics, you are only changing the Physics object. If you want a different scoring system, you only change the Game object. This is the benefit of using a modular design and why it is crucial to object oriented programming.

The Game Entity objects Player and Enemy are the same except they no longer move themselves. Notice that they are insulated from the canvas by asking the game object for the height of the game field. As discussed above, we are going to create three new objects, the Renderer, Physics and Game objects.

These will be singletons. Generally speaking, the Game Entities, Physics and Renderer should be largely reusable, with specific extensions and modifications, while the Game object will be very specific to each game you make.

Rendering is really quite simple. It gets the Game Entities from the Game object and draws based on the type of entity. This is obviously a very simple renderer. In a more complicated one, it would be loading textures and sprites, depth sorting, etc. The Physics object operates in the same way.

It gets the Game Entities from the Game object and applies the motion. Obviously this is also highly simplistic, but you will easily place real physics code in this spot. The Game object brings it all together. It is the owner of all the other objects and where the game loop is processed.

In the update function you would add things like checking for the win and lose conditions and the logic unique to the particular game. So there you have it, the most basic, yet correctly structured, game engine I could think of. I really hope you found this tutorial helpful. To demonstrate an actual game using this framework, I wrote a tutorial series that creates a Space Invaders clone from scratch.

We have to create to the new property in the component's constructor and call them speed A, speed B. We will use these following properties as the speed indicators. The function newPos ; will be called from the body of the "updatemygame ;" function just before the drawing the component. Let's see how we can create obstacles by creating a new component and adding it to the gaming area.

To provide the movement to our obstacles, we have to change the property of the "myfirstObstacle. As we all know that, in any game, if the user hits any obstacle, then the game is over. To do this, we need to create a new method in the component's constructor, which will look for the collision of our blue box with other constraints or any other component from the beginning of the game. This method must be executed repeatedly each time a frame update is received or we can say that this method should be called 50 times in a second.

We will also have to add the stop ; method to the mygamearea' s object that will clear the millisecond interval. To make our game a little more difficult and interesting, add random-sized obstacles so that the user moves the blue box continuously in different directions to avoid hitting the obstacles. For displaying the user's score, there are many different ways, but to keep this game as simple as possible, we will use one of the easiest methods. In this method, we have to create a new variable first, e.

So it is necessary to invoke the component's constructor using the additional argument that will tell the constructor about the type of component, which is "text" type in this case. In the component's constructor, we will test the type of the component e. Finally, we will use the FrameNo property to count the score. To implement this, we have to modify some code of the "updateGameArea ;" function that will use the FrameNo property and write the canvas score.

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