Canvas spatial grid collision

Question

You can see a working example here. Be sure to click on the canvas or the key inputs will not be detected!

Are there any ways I could improve upon this? Anything that should have been done differently? Any best practices I have not implemented?

$(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);
});

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.

• ShaShads: Thank you this has helped! This is my first ever game so I just tried to throw something together. I will try and improve on it.