CODEWITHSUNDEEP
javascripthtmlcanvascollision-detection
Someone
Someone

Reputation: 3568

Javascript Canvas Game - Collision Detection

I'm building a little mini tile engine game. I'm currently working on implementing simple block based collision detection, however I'm having real problems. I've googled this for hours looking at different implementations but can't seem to get my head around it. My current effort (only currently detecting collisions when the player moves right), mostly works but allows the player to pass through the bottom part of the obstacle. The collision uses the normal map array to detect collisions, any value of 2 in the map is a solid object.

I understand the concepts of what I need to do - before I move my player, calculate what cell the player will end up in. Check what value has been assigned to that cell. If it is 2, don't allow the player to move.

My issue is figuring out what cell the player will end up in as technically, at points, the player can be in 4 cells at the same time. I've tried using origins and 4 corner detection to get around this, but I just can't get it working.

JS Fiddle HERE - https://jsfiddle.net/j1xqxze8/

My Code;

    var Player = function() {
        this.width = 16;
        this.height = 16;
        this.position   = {};
        this.position.x = 32;
        this.position.y = 32;
        this.speed      = 8;

        this.render = function() {
            window.context.fillStyle = 'white';
            window.context.fillRect(this.position.x, this.position.y, this.width, this.height);
        };

        var _self = this;

        this.didCollide = function(dir) {
            if(dir == 'right'){
                var newBlock = window.tileMap.getCell(Math.floor((_self.position.x + _self.width) / 32), Math.floor((this.position.y + this.height / 2) / 32));

                if(newBlock == 2)
                    return true;
            }
        };

        window.addEventListener('keydown', function(e) {
            if(e.keyCode == 38 || e.keyCode == 87){
                _self.position.y -= _self.speed;
            }

            if(e.keyCode == 40 || e.keyCode == 83){
                _self.position.y += _self.speed;
            }

            if(e.keyCode == 37 || e.keyCode == 65){
                _self.position.x -= _self.speed;
            }

            if(e.keyCode == 39 || e.keyCode == 68){
                if(!_self.didCollide('right')){
                    _self.position.x += _self.speed;
                }
            }
        })
    };

var TileMap = function() {
    this.map = [
        [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 2, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1],
        [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]
    ];

    this.tileSize = 32;
    this.colors = ['black', 'red', 'green'];

    this.getCell = function(x, y){
      return this.map[y][x];
    };

        this.render = function(){
            for(var x = 0; x < this.map.length; x++){
                for(var y = 0; y < this.map.length; y++){
                    // SWAP Y AND X IN THE FILLSTYLE DUE TO BACKWARDS/MIRRORED JS ARRAY READING
                    window.context.fillStyle = this.colors[this.map[y][x]];
                    window.context.fillRect((x * this.tileSize) - window.camera.position.x, (y * this.tileSize) - window.camera.position.y, this.tileSize, this.tileSize);

                    window.context.strokeStyle = 'yellow';
                    window.context.strokeRect((x * this.tileSize) - window.camera.position.x, (y * this.tileSize) - window.camera.position.y, this.tileSize, this.tileSize);
                }
            }
        }
    };

Upvotes: 5

Views: 956

Answers (2)

markE
markE

Reputation: 105015

Since you are moving the player 8 positions per keydown, in keydown you must test each of those 8 interim positions to see if a collision occurs.

Warning: untested code -- some tweaking (probably!) required

window.addEventListener('keydown', function(e) {
    // save x,y before the move
    var beginningX=_self.position.x;
    var beginningY=_self.position.y;

    // test each interim positon between the beginning & 
    // current position for collisions
    // if a collision occurs, stop at the collision position
    if(e.keyCode == 38 || e.keyCode == 87){
        _self.position.y -= _self.speed;
        _self.position.y = testInterimVerticalCollisions(
            beginningY, _self.position.y, _self.position.x);
    }

    if(e.keyCode == 40 || e.keyCode == 83){
        _self.position.y += _self.speed;
        _self.position.y = testInterimVerticalCollisions(
            beginningY, _self.position.y, _self.position.x);
    }

    if(e.keyCode == 37 || e.keyCode == 65){
        _self.position.x -= _self.speed;
        _self.position.x = testInterimHorizontalCollisions(
            beginningX, _self.position.x, _self.position.y);
    }

    if(e.keyCode == 39 || e.keyCode == 68){
        _self.position.x += _self.speed;
        _self.position.x = testInterimHorizontalCollisions(
            beginningX, _self.position.x, _self.position.y);
        }
    }
})

// test if any interim movement caused a collision
// if yes, return the x that caused the collision
// if no, return the ending x
function testInterimHorizontalCollisions(beginningX,endingX,y){
    for(var x=beginningX;x<=endingX;x++){
        // TODO: adjust for camera position offset
        var cellX = parseInt(x/cellWidth);
        var cellY = parseInt(y/cellHeight);
        if(getCell(cellX,cellY)==2){return(x);}
    }
    return(endingX);
}

// test if any interim movement caused a collision
// if yes, return the y that caused the collision
// if no, return the ending y
function testInterimVerticalCollisions(beginningY,endingY,x){
    for(var y=beginningY;y<=endingY;y++){
        // TODO: adjust for camera position offset
        var cellX = parseInt(x/cellWidth);
        var cellY = parseInt(y/cellHeight);
        if(getCell(cellX,cellY)==2){return(y);}
    }
    return(endingY);
}

Upvotes: 1

Bobby Orndorff
Bobby Orndorff

Reputation: 3335

You need to compute the new position of the player by adding/subtracting speed to/from current x/y position. Then you need to compute the range of pixels covered by the player in the new position. Then you need to compute the range of cells corresponding to the range of pixels. Then you need to loop through the range of cells to see if there are any collisions. Note that when computing the right/bottom pixel covered by the player, you need to add x/y and width/height and then subtract 1.

Change...

this.didCollide = function(dir) {
    if(dir == 'right'){
        var newBlock = window.tileMap.getCell(Math.floor((_self.position.x + _self.width) / 32), Math.floor((this.position.y + this.height / 2) / 32));
        if(newBlock == 2)
            return true;
    }
};

to...

this.didCollide = function(dir) {
    if(dir == 'right'){
        var col1 = Math.floor((_self.position.x + _self.speed) / 32);
        var col2 = Math.floor((_self.position.x + _self.speed + _self.width - 1) / 32);
        var row1 = Math.floor((_self.position.y) / 32);
        var row2 = Math.floor((_self.position.y + _self.height - 1) / 32);
        document.getElementById("player").textContent = "player: " + _self.position.x + " " + _self.position.y + " " + _self.width + " " + _self.height;
        document.getElementById("cells").textContent = "cells: " + col1 + " " + col2 + " " + row1 + " " + row2;
        for (var c = col1; c <= col2; c++) {
            for (var r = row1; r <= row2; r++) {
                var newBlock = window.tileMap.getCell(c, r);
                if(newBlock == 2) {
                    return true;
                }
            }
        }
    }
    return false;
};

Upvotes: 2

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