Tutorial game canvas

Now for input handling. This is probably the first part that will trip up developers who come from a web development background. In the web stack, it may be appropriate to begin animating or requesting data right when the user initiates input.

But in this flow, we want our game's logic to live solely in once place to retain tight control over when and if things happen. For that reason we just want to store the user input for later instead of acting on it immediately. To accomplish this we simply have a variable keysDown which stores any event's keyCode.

If a key code is in the object, the user is currently pressing that key. The reset function is called to begin a new game, or level, or whatever you'd like to call it.

It places the hero the player in the center of the screen and the monster somewhere randomly. This is the update function and is called every single interval execution.

The first thing it does is checks the up, down, left, and right arrow keys to see if the user has pressed them. If so, the hero is moved in the corresponding direction.

What may seem odd is the modifier argument passed into update. You'll see how this is referenced in the main function, but let me first explain it here. If exactly one second has passed, the value will be 1 and the hero's speed will be multiplied by 1, meaning he will have moved pixels in that second.

If one half of a second has passed, the value will be 0. And so forth. This function gets called so rapidly that the modifier value will typically be very low, but using this pattern will ensure that the hero will move the same speed no matter how fast or slowly!

When the player clicks on it, the score on the square increases, the direction in which the square is traveling changes and the speed of the square increases. First, we define some objects and properties. The level defines the area in which the square can bounce around. The square itself has a position, dimensions and movement properties.

Finally, there is a score. The square needs to be moved and collisions with the edges of the level should be detected and resolved. We need to draw the square and the score. This needs to be done in the render function. The title of the demo should be modified in the drawFrame function. The final step is to add mouse interactions. This is the 1st step out of 10 of the Gamedev Canvas tutorial.

Before we can start writing the game's functionality, we need to create a basic structure to render the game inside. Using your favorite text editor, create a new HTML document, save it as index. Then we're creating the ctx variable to store the 2D rendering context — the actual tool we can use to paint on the Canvas. Let's see an example piece of code that prints a red square on the canvas.

Add this below your previous lines of JavaScript, then load your index. All the instructions are between the beginPath and closePath methods.