My first attempt at canvas spatial grid collision? Please be honest!

Question

The code,

$(document).ready(function() {

window.addEventListener('keydown', keyPress, true); // event listener for keyboard presses
function keyPress(evt) {
    if(engine.activeBlock) { // block is actively falling
        switch(evt.keyCode) {
            case 37: // left arrow
                engine.activeBlock.keyLeft();
            break;
            case 39: // right arrow
                engine.activeBlock.keyRight();
            break;
            case 40: // down arrow
                engine.activeBlock.keyDown();
            break;
        }
    }
}

// block object
function block() {
    this.xStart = function() { // random x coordinate of starting position of block
        var x = Math.floor(Math.random() * (engine.cellsX - 1 + 1)) + 1; // random number between 1 and cellsX
        return (x - 1) * engine.cellSize;
    };
    this.x = this.xStart(); // x coordinate
    this.y = 0 - (engine.cellSize * 1.5); // y coordinate
    this.velocity = 1; // velocity of the block
    this.generateColor = function() { // generates a random color
        var colors = ['blue', 'red', 'green', 'black', 'orange']; // colors array
        return colors[Math.floor(Math.random() * colors.length)];
    };
    this.color = this.generateColor(); // color of the block
    this.keyLeft = function() { // key left
        if(!engine.collisionLeft()) { // check collisions left side
            this.x -= engine.cellSize;
        }
    };
    this.keyRight = function() { // key right
        if(!engine.collisionRight()) { // check collisions right side
            this.x += engine.cellSize;
        }
    };
    this.keyDown = function() { // key down
        if(this.y > 0) { // block is on screen
            this.velocity += 1; // increase block velocity
        }
    };
    this.update = function() { // updates the blocks position
        this.y += this.velocity; // increase velocity
        engine.collisionBelow(); // check collisions below
        ctx.fillStyle = this.color;
        ctx.fillRect(this.x, this.y, engine.cellSize, engine.cellSize);
    };
}

// engine object
function engine() {
    this.cellSize = 100; // size of each cell
    this.cellsX = canvas.width / this.cellSize; // number of cells along the x axis
    this.cellsY = canvas.height / this.cellSize; // number of cells along the y axis
    this.totalCells = this.cellsX * this.cellsY; // total cells
    this.buildGrid = function() { // builds grid
        var arr = new Array(this.cellsX);
        for(var i = 0; i < arr.length; ++i) {
            arr[i] = new Array(this.cellsY);
        }
        return arr;
    };
    this.grid = this.buildGrid(); // holds grid
    this.activeBlock = false; // where a falling block is placed
    this.getGridCoords = function(i) { // x coordinate of where a block should be placed in grid
        return Math.floor(i / this.cellSize);
    };
    this.drawGrid = function() { // outputs the blocks stored in grid
        for(var i = 0; i < this.grid.length; ++i) {
            for(var i2 = 0; i2 < this.grid[i].length; ++i2) {
                if(this.grid[i][i2]) { // grid cell is occupied
                    ctx.fillStyle = this.grid[i][i2].color;
                    ctx.fillRect(this.grid[i][i2].x, this.grid[i][i2].y, this.cellSize, this.cellSize);
                }
            }
        }
    };
    this.collisionBelow = function() { // check collisions below
        if(this.activeBlock.y > (canvas.height - this.cellSize)) {
            this.insertBlock(); // insert block into grid
        } else if(this.grid[this.getGridCoords(this.activeBlock.x)][this.getGridCoords(this.activeBlock.y) + 1]) {
            this.insertBlock(); // insert block into grid
        }
    };
    this.collisionLeft = function() { // check collisions left
        if(this.activeBlock.x <= 0) {
            return true;
        } else if(this.grid[this.getGridCoords(this.activeBlock.x) - 1][this.getGridCoords(this.activeBlock.y)]) {
            return true;
        } else if(this.grid[this.getGridCoords(this.activeBlock.x) - 1][this.getGridCoords(this.activeBlock.y) - 1]) {
            return true;
        } else if(this.grid[this.getGridCoords(this.activeBlock.x) - 1][this.getGridCoords(this.activeBlock.y) + 1]) {
            return true;
        }
    };
    this.collisionRight = function() { // check collisions right
        if(this.activeBlock.x >= (canvas.width - this.cellSize)) {
            return true;
        } else if(this.grid[this.getGridCoords(this.activeBlock.x) + 1][this.getGridCoords(this.activeBlock.y)]) {
            return true;
        } else if(this.grid[this.getGridCoords(this.activeBlock.x) + 1][this.getGridCoords(this.activeBlock.y) - 1]) {
            return true;
        } else if(this.grid[this.getGridCoords(this.activeBlock.x) + 1][this.getGridCoords(this.activeBlock.y) + 1]) {
            return true;
        }
    };
    this.insertBlock = function() { // insert block into grid
        this.activeBlock.x = this.cellSize * Math.floor(this.activeBlock.x / this.cellSize); // floor x coordinate to cellSize multiple
        this.activeBlock.y = this.cellSize * Math.floor(this.activeBlock.y / this.cellSize); // floor y coordinate to cellSize multiple
        this.grid[this.getGridCoords(this.activeBlock.x)][this.getGridCoords(this.activeBlock.y)] = this.activeBlock;
        this.activeBlock = new block();
    };
}

var canvas = $('canvas')[0]; // holds the canvas
var ctx = canvas.getContext('2d'); // holds the canvas context
var engine = new engine(); // initiate the engine
engine.activeBlock = new block(); // add block

function loop() { // game loop
    ctx.fillStyle = '#eee';
    ctx.fillRect(0, 0, canvas.width, canvas.height);
    engine.activeBlock.update(); // update active block
    engine.drawGrid(); // draw the grid of blocks
}

// run loop
setInterval(loop, 20);
});

You can see a working example here http://jsfiddle.net/ShaShads/GuL5K/1/embedded/result/ be sure to click on the canvas or the key inputs will not be detected!

Are there anyways I could improve upon this? Anything that should have been done differently? Any best practices I have not implemented? I am still learning so if there is alot I apologize!!

Answer 1

Haven't looked at the code in detail, but here are some thoughts on the overall structure:

Right now, there's some mixing of concerns and tight coupling going on. The engine calls update on the active block, but the block then calls back to the engine to check for collisions. In other words, the two are tightly coupled; they're dependent on each other, and its unclear where certain responsibilities lie.

The block is a pretty simple object, which can be reduced to simply being an x, y position, and a velocity. And it should probably stop there. The engine would be responsible for moving the block (the block object can do the calculations, though), checking collisions, accepting keyboard input, etc.. I.e. keep the block "dumb"; it doesn't need to know its context.

I'd also suggest making a similarly "dumb" grid object that the engine object can interrogate and instruct. I.e. the grid doesn't move blocks around, it simply keeps track of them for the engine. The grid could check for collisions, but it'd be up to the engine to ask.

Where exactly to draw the boundaries between the objects and their responsibilities is up to you (there are many ways to break it down), but the idea is to keep things decoupled when possible. I.e. blocks don't rely on a grid or an engine being there; the grid may or may not care about blocks being blocks, just that there's something in a given cell, etc.. Perhaps there are more things, you can extract and/or abstract and encapsulate in objects or constructors, while the engine sits in the middle acting as controller.

On a purely syntactical level, I'd move the methods of into the prototypes for the objects. That is, from this

function block() {
  // instance variables ...
  this.update = function () { ... }
}

to this

function Block() {  // CamelCase since it's a constructor
  // instance variables ...
}

Block.prototype.update = function () {
  ...
};

This will make it easier to do prototypal inheritance, as the methods will actually be prototypal.