IDEA 编写HTML小游戏 之 《超级玛丽终极版》

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<style type="text/css">
*body{margin:0 auto;}
#status{
position: absolute;
left: 50%;
top: 170px;
margin-left: 60px;
}
.background {
background: rgb(52, 166, 251);
table-layout: fixed;
border-spacing: 0;
}
.background td { padding: 0; }
.lava { background: rgb(255, 100, 100); }
.wall { background: white; }
.actor { position: absolute; }
.coin { background: rgb(241, 229, 89); }
.player { background: rgb(64, 64, 64); }
.lost .player { background: rgb(160, 64, 64); }
.won .player {
box-shadow: -4px -7px 8px white, 4px -7px 8px white;
}
.game {
overflow: hidden;
max-width: 600px;
max-height: 450px;
position: relative;
}
</style>
</head>

<body>
<img style="position: absolute;right: 0;top: 0;" src=" http://a4.qpic.cn/psb?/V13id91S0o4nYt/y9R.1dX5WxfYfZzDqBMG2hsjLT7LiZjPoCPYg.6gxhk!/b/dEMBAAAAAAAA&ek=1&kp=1&pt=0&bo=LAGyAQAAAAARF74!&vuin=206105759&tm=1522486800&sce=60-2-2&rf=viewer_4">
<div id='status'>How many lives you have left: <span id="lives"></span></div>
<script type="text/javascript">

/*

Based on Dark Blue by Thomas Palef.
Plans are submitted as an array of strings that forms a grid.
@ = Player start position
o = Coins
x = Solid surfaces
! = Non-moving lava
= = Vertical moving lava
v = Dripping lava
| = Horizontal moving lava
*/
var simpleLevelPlan = [
" ",
" ",
" x = x ",
" x o o x ",
" x @ xxxxx x ",
" xxxxx x ",
" x!!!!!!!!!!!!x ",
" xxxxxxxxxxxxxx ",
" "
];

var GAME_LEVELS = [
    ["                                                                                ",
        "                                                                                ",
        "                                                                                ",
        "                                                                                ",
        "                                                                                ",
        "                                                                                ",
        "                                                                  xxx           ",
        "                                                   xx      xx    xx!xx          ",
        "                                    o o      xx                  x!!!x          ",
        "                                                                 xx!xx          ",
        "                                   xxxxx                          xvx           ",
        "                                                                            xx  ",
        "  xx                                      o o                                x  ",
        "  x                     o                                                    x  ",
        "  x                                      xxxxx                             o x  ",
        "  x          xxxx       o                                                    x  ",
        "  x  @       x  x                                                xxxxx       x  ",
        "  xxxxxxxxxxxx  xxxxxxxxxxxxxxx   xxxxxxxxxxxxxxxxxxxx     xxxxxxx   xxxxxxxxx  ",
        "                              x   x                  x     x                    ",
        "                              x!!!x                  x!!!!!x                    ",
        "                              x!!!x                  x!!!!!x                    ",
        "                              xxxxx                  xxxxxxx                    ",
        "                                                                                ",
        "                                                                                "],
    ["                                      x!!x                        xxxxxxx                                    x!x  ",
        "                                      x!!x                     xxxx     xxxx                                 x!x  ",
        "                                      x!!xxxxxxxxxx           xx           xx                                x!x  ",
        "                                      xx!!!!!!!!!!xx         xx             xx                               x!x  ",
        "                                       xxxxxxxxxx!!x         x                                    o   o   o  x!x  ",
        "                                                xx!x         x     o   o                                    xx!x  ",
        "                                                 x!x         x                                xxxxxxxxxxxxxxx!!x  ",
        "                                                 xvx         x     x   x                        !!!!!!!!!!!!!!xx  ",
        "                                                             xx  |   |   |  xx            xxxxxxxxxxxxxxxxxxxxx   ",
        "                                                              xx!!!!!!!!!!!xx            v                        ",
        "                                                               xxxx!!!!!xxxx                                      ",
        "                                               x     x            xxxxxxx        xxx         xxx                  ",
        "                                               x     x                           x x         x x                  ",
        "                                               x     x                             x         x                    ",
        "                                               x     x                             xx        x                    ",
        "                                               xx    x                             x         x                    ",
        "                                               x     x      o  o     x   x         x         x                    ",
        "               xxxxxxx        xxx   xxx        x     x               x   x         x         x                    ",
        "              xx     xx         x   x          x     x     xxxxxx    x   x   xxxxxxxxx       x                    ",
        "             xx       xx        x o x          x    xx               x   x   x               x                    ",
        "     @       x         x        x   x          x     x               x   x   x               x                    ",
        "    xxx      x         x        x   x          x     x               x   xxxxx   xxxxxx      x                    ",
        "    x x      x         x       xx o xx         x     x               x     o     x x         x                    ",
        "!!!!x x!!!!!!x         x!!!!!!xx     xx!!!!!!!!xx    x!!!!!!!!!!     x     =     x x         x                    ",
        "!!!!x x!!!!!!x         x!!!!!xx       xxxxxxxxxx     x!!!!!!!xx!     xxxxxxxxxxxxx xx  o o  xx                    ",
        "!!!!x x!!!!!!x         x!!!!!x    o                 xx!!!!!!xx !                    xx     xx                     ",
        "!!!!x x!!!!!!x         x!!!!!x                     xx!!!!!!xx  !                     xxxxxxx                      ",
        "!!!!x x!!!!!!x         x!!!!!xx       xxxxxxxxxxxxxx!!!!!!xx   !                                                  ",
        "!!!!x x!!!!!!x         x!!!!!!xxxxxxxxx!!!!!!!!!!!!!!!!!!xx    !                                                  ",
        "!!!!x x!!!!!!x         x!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!xx     !                                                  "],
    ["                                                                                                              ",
        "                                                                                                              ",
        "                                                                                                              ",
        "                                                                                                              ",
        "                                                                                                              ",
        "                                        o                                                                     ",
        "                                                                                                              ",
        "                                        x                                                                     ",
        "                                        x                                                                     ",
        "                                        x                                                                     ",
        "                                        x                                                                     ",
        "                                       xxx                                                                    ",
        "                                       x x                 !!!        !!!  xxx                                ",
        "                                       x x                 !x!        !x!                                     ",
        "                                     xxx xxx                x          x                                      ",
        "                                      x   x                 x   oooo   x       xxx                            ",
        "                                      x   x                 x          x      x!!!x                           ",
        "                                      x   x                 xxxxxxxxxxxx       xxx                            ",
        "                                     xx   xx      x   x      x                                                ",
        "                                      x   xxxxxxxxx   xxxxxxxx              x x                               ",
        "                                      x   x           x                    x!!!x                              ",
        "                                      x   x           x                     xxx                               ",
        "                                     xx   xx          x                                                       ",
        "                                      x   x= = = =    x            xxx                                        ",
        "                                      x   x           x           x!!!x                                       ",
        "                                      x   x    = = = =x     o      xxx       xxx                              ",
        "                                     xx   xx          x                     x!!!x                             ",
        "                              o   o   x   x           x     x                xxv        xxx                   ",
        "                                      x   x           x              x                 x!!!x                  ",
        "                             xxx xxx xxx xxx     o o  x!!!!!!!!!!!!!!x                   vx                   ",
        "                             x xxx x x xxx x          x!!!!!!!!!!!!!!x                                        ",
        "                             x             x   xxxxxxxxxxxxxxxxxxxxxxx                                        ",
        "                             xx           xx                                         xxx                      ",
        "  xxx                         x     x     x                                         x!!!x                xxx  ",
        "  x x                         x    xxx    x                                          xxx                 x x  ",
        "  x                           x    xxx    xxxxxxx                        xxxxx                             x  ",
        "  x                           x           x                              x   x                             x  ",
        "  x                           xx          x                              x x x                             x  ",
        "  x                                       x       |xxxx|    |xxxx|     xxx xxx                             x  ",
        "  x                xxx             o o    x                              x         xxx                     x  ",
        "  x               xxxxx       xx          x                             xxx       x!!!x          x         x  ",
        "  x               oxxxo       x    xxx    x                             x x        xxx          xxx        x  ",
        "  x                xxx        xxxxxxxxxxxxx  x oo x    x oo x    x oo  xx xx                    xxx        x  ",
        "  x      @          x         x           x!!x    x!!!!x    x!!!!x    xx   xx                    x         x  ",
        "  xxxxxxxxxxxxxxxxxxxxxxxxxxxxx           xxxxxxxxxxxxxxxxxxxxxxxxxxxxx     xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx  ",
        "                                                                                                              ",
        "                                                                                                              "],
    ["                                                                                                  xxx x       ",
        "                                                                                                      x       ",
        "                                                                                                  xxxxx       ",
        "                                                                                                  x           ",
        "                                                                                                  x xxx       ",
        "                          o                                                                       x x x       ",
        "                                                                                             o o oxxx x       ",
        "                   xxx                                                                                x       ",
        "       !  o  !                                                xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxx       ",
        "       x     x                                                x   x x   x x   x x   x x   x x   x x           ",
        "       x= o  x            x                                   xxx x xxx x xxx x xxx x xxx x xxx x xxxxx       ",
        "       x     x                                                  x x   x x   x x   x x   x x   x x     x       ",
        "       !  o  !            o                                  xxxx xxxxx xxxxx xxxxx xxxxx xxxxx xxxxxxx       ",
        "                                                                                                              ",
        "          o              xxx                              xx                                                  ",
        "                                                                                                              ",
        "                                                                                                              ",
        "                                                      xx                                                      ",
        "                   xxx         xxx                                                                            ",
        "                                                                                                              ",
        "                          o                                                     x      x                      ",
        "                                                          xx     xx                                           ",
        "             xxx         xxx         xxx                                 x                  x                 ",
        "                                                                                                              ",
        "                                                                 ||                                           ",
        "  xxxxxxxxxxx                                                                                                 ",
        "  x         x o xxxxxxxxx o xxxxxxxxx o xx                                                x                   ",
        "  x         x   x       x   x       x   x                 ||                  x     x                         ",
        "  x  @      xxxxx   o   xxxxx   o   xxxxx                                                                     ",
        "  xxxxxxx                                     xxxxx       xx     xx     xxx                                   ",
        "        x=                  =                =x   x                     xxx                                   ",
        "        xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx   x!!!!!!!!!!!!!!!!!!!!!xxx!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!",
        "                                                  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx",
        "                                                                                                              "]
];

// Assumes the plan is valid (add validation for production)
function Level(plan) {
    this.width = plan[0].length;
    this.height = plan.length;
    // Array of arrays, each position containing null or a character
    this.grid = [];
    // Contains all of the dynamic objects (lava, coin or player),
    // along with their position and state
    this.actors = [];

    for (var y = 0; y < this.height; y++) {
        var line = plan[y], gridLine = [];
        for (var x = 0; x < this.width; x++) {
            var ch = line[x], fieldType = null;
            var Actor = actorChars[ch];
            if (Actor)
                // This constructs the referenced moving object in
                // actorChars and pushes it to the actors array
                this.actors.push(new Actor(new Vector(x, y), ch));
            else if (ch == 'x')
                // Wall
                fieldType = 'wall';
            else if (ch == '!')
                // Stationary lava
                fieldType = 'lava';
            gridLine.push(fieldType);
        }
        this.grid.push(gridLine);
    }
    // Find the Player actor
    this.player = this.actors.filter(function(actor) {
        return actor.type == 'player';
    })[0];
    // Track whether the player has won or lost;
    // finishDelay keeps the level active for a brief period of time
    this.status = this.finishDelay = null;
}
// Figure out if the level is finished
Level.prototype.isFinished = function() {
    return this.status != null && this.finishDelay < 0;
};
// Figure out the collision area of an actor
Level.prototype.obstacleAt = function(pos, size) {
    var xStart = Math.floor(pos.x);
    var xEnd = Math.ceil(pos.x + size.x);
    var yStart = Math.floor(pos.y);
    var yEnd = Math.ceil(pos.y + size.y);

    // The upper and side bounds of the level return a wall
    if (xStart < 0 || xEnd > this.width || yStart < 0)
        return 'wall';
    // The bottom bound returns lava
    if (yEnd > this.height)
        return 'lava';
    // Check what's on the grid around the collision box
    for (var y = yStart; y < yEnd; y++) {
        for (var x = xStart; x < xEnd; x++) {
            var fieldType = this.grid[y][x];
            // returns 'wall' or 'lava'
            if (fieldType) return fieldType;
        }
    }
};
// Track what actors overlap a given actor
Level.prototype.actorAt = function(actor) {
    for (var i = 0; i < this.actors.length; i++) {
        var other = this.actors[i];
        if (other != actor &&
            actor.pos.x + actor.size.x > other.pos.x &&
            actor.pos.x < other.pos.x + other.size.x &&
            actor.pos.y + actor.size.y > other.pos.y &&
            actor.pos.y < other.pos.y + other.size.y)
            return other;
    }
};
// Time increment for Level.animate()
var maxStep = 0.05;
// Animate the level
// step will be given in seconds, keys is an object that
// contains info about the arrow keys the player has pressed.
Level.prototype.animate = function(step, keys) {
    // Used for the delay at the end of a game
    if (this.status != null)
        this.finishDelay -= step;

    while (step > 0) {
        var thisStep = Math.min(step, maxStep);
        this.actors.forEach(function(actor) {
            actor.act(thisStep, this, keys);
        }, this);
        step -= thisStep;
    }
};
// Handle collisions between actors
Level.prototype.playerTouched = function(type, actor) {
    // Lava's been touched
    if (type == 'lava' && this.status == null) {
        this.status = 'lost';
        this.finishDelay = 1;
    } else if (type == 'coin') { // a coin's been touched
        // Remove the coin that's been collected from actors array
        this.actors = this.actors.filter(function(other) {
            return other != actor;
        });
        // No more coins = you've won
        if (!this.actors.some(function(actor) {
            return actor.type == 'coin';
        })) {
            this.status = 'won';
            this.finishDelay = 1;
        }
    }
}

var actorChars = {
    '@': Player,
    'o': Coin,
    '=': Lava, '|': Lava, 'v': Lava
};

// Vector stores the position and size of an actor
function Vector(x, y) {
    this.x = x; this.y = y;
}
Vector.prototype.plus = function(other) {
    return new Vector(this.x + other.x, this.y + other.y);
}
Vector.prototype.times = function(factor) {
    return new Vector(this.x * factor, this.y * factor);
}

// Player constructor
function Player(pos) {
    // This properly aligns the bottom of the player
    // to the square below (adjusts for player height)
    this.pos = pos.plus(new Vector(0, -0.5));
    this.size = new Vector(0.8, 1.5);
    this.speed = new Vector(0, 0);
}
Player.prototype.type = 'player';
// X and Y movement are handled independently because
// a wall shouldn't stop the up and down motion of jumping
// and a floor shouldn't stop side to side movement
var playerXSpeed = 7;
Player.prototype.moveX = function(step, level, keys) {
    this.speed.x = 0;
    if (keys.left) this.speed.x -= playerXSpeed;
    if (keys.right) this.speed.x += playerXSpeed;

    var motion = new Vector(this.speed.x * step, 0);
    var newPos = this.pos.plus(motion);
    var obstacle = level.obstacleAt(newPos, this.size);
    if (obstacle)
        level.playerTouched(obstacle);
    else
        this.pos = newPos;
};
var gravity = 30;
var jumpSpeed = 17;
Player.prototype.moveY = function(step, level, keys) {
    this.speed.y += step * gravity;
    var motion = new Vector(0, this.speed.y * step);
    var newPos = this.pos.plus(motion);
    var obstacle = level.obstacleAt(newPos, this.size);
    if (obstacle) {
        level.playerTouched(obstacle);
        if (keys.up && this.speed.y > 0)
            this.speed.y = -jumpSpeed;
        else
            this.speed.y = 0;
    } else {
        this.pos = newPos;
    }
};
Player.prototype.act = function(step, level, keys) {
    this.moveX(step, level, keys);
    this.moveY(step, level, keys);

    var otherActor = level.actorAt(this);
    if (otherActor)
        level.playerTouched(otherActor.type, otherActor);

    // Losing animation
    if (level.status == 'lost') {
        this.pos.y += step;
        this.size.y -=step;
    }
};

// Lava constructor
function Lava(pos, ch) {
    this.pos = pos;
    this.size = new Vector(1, 1);
    if (ch == "=") {
        // I'm guessing that speed will be added to this.pos
        // in a moving method added later
        this.speed = new Vector(2, 0);
    } else if (ch == '|') {
        this.speed = new Vector(0, 2);
    } else if (ch == 'v') {
        this.speed = new Vector(0, 3);
        this.repeatPos = pos;
    }
}
Lava.prototype.type = 'lava';
// Action
Lava.prototype.act = function(step, level) {
    var newPos = this.pos.plus(this.speed.times(step));
    if (!level.obstacleAt(newPos, this.size))
        this.pos = newPos;
    else if (this.repeatPos)
        this.pos = this.repeatPos;
    else
        this.speed = this.speed.times(-1);
};

// Coin constructor
function Coin(pos) {
    this.basePos = this.pos = pos.plus(new Vector(0.2, 0.1));
    this.size = new Vector(0.6, 0.6);
    this.wobble = Math.random() * Math.PI * 2;
}
Coin.prototype.type = 'coin';
var wobbleSpeed = 8, wobbleDist = 0.07;
// Action
Coin.prototype.act = function(step) {
    this.wobble += step * wobbleSpeed;
    var wobblePos = Math.sin(this.wobble) * wobbleDist;
    this.pos = this.basePos.plus(new Vector(0, wobblePos));
};

// Helper function that creates an element
// and gives it a class
function elt(name, className) {
    var elt = document.createElement(name);
    if (className) elt.className = className;
    return elt;
}

// Tracking keypresses for player movement
var arrowCodes = {37: 'left', 38: 'up', 39: 'right'};

function trackKeys(codes) {
    var pressed = Object.create(null);
    function handler(event) {
        if (codes.hasOwnProperty(event.keyCode)) {
            var down = event.type == 'keydown';
            pressed[codes[event.keyCode]] = down;
            event.preventDefault();
        }
    }
    addEventListener('keydown', handler);
    addEventListener('keyup', handler);

    pressed.unregister = function() {
        removeEventListener('keydown', handler);
        removeEventListener('keyup', handler);
    };

    return pressed;
}

// Run the animation
function runAnimation(frameFunc) {
    var lastTime = null;
    function frame(time) {
        var stop = false;
        if (lastTime != null) {
            var timeStep = Math.min(time - lastTime, 100) / 1000;
            stop = frameFunc(timeStep) === false;
        }
        lastTime = time;
        if (!stop)
            requestAnimationFrame(frame);
    }
    requestAnimationFrame(frame);
}

// Run the level
var arrows = trackKeys(arrowCodes);

function runLevel(level, Display, andThen) {
    var display = new Display(document.body, level);
    // Used for storing pause state of the game
    var running = 'yes';

    function handleKey(event) {
        if (event.keyCode == 27) {
            if (running == 'no') {
                running = 'yes';
                runAnimation(animation);
            } else if (running == 'pausing') {
                running = 'yes';
            } else if (running == 'yes') {
                running = 'pausing';
            }
        }
    }
    addEventListener('keydown', handleKey);

    function animation(step) {
        if (running == 'pausing') {
            running = 'no';
            return false;
        }

        level.animate(step, arrows);
        display.drawFrame(step);
        if (level.isFinished()) {
            display.clear();
            // Remove the watch on the esc key
            //removeEventListener('keydown', handleKey);
            // Unregister the arrow key listeners
            //arrows.unregister();
            if (andThen)
                andThen(level.status);
            return false;
        }
    }

    runAnimation(animation);
}

// Run the game
function runGame(plans, Display) {
    var lives = 3;
    var livesSpan = document.getElementById('lives');
    var gameStatus = document.getElementById('status');

    function startLevel(n) {
        livesSpan.textContent = lives;
        runLevel(new Level(plans[n]), Display, function(status) {
            if (status == 'lost') {
                lives--;
                if (lives == 0) {
                    gameStatus.textContent = 'Game Over';
                    console.log('Game over');
                }
                else
                    startLevel(n);
            }
            else if (n < plans.length - 1)
                startLevel(n + 1);
            else
                console.log('You win!');
        });
    }
    startLevel(0);
}


// DOMDisplay uses the DOM to draw the program out
function DOMDisplay(parent, level) {
    this.wrap = parent.appendChild(elt('div', 'game'));
    this.level = level;

    // Background is drawn only once
    this.wrap.appendChild(this.drawBackground());
    // The actorLayer is animated in the drawFrame() method
    this.actorLayer = null;
    this.drawFrame();
}
// Set the scale of 1 grid unit
var scale = 20;
// Draw the background
DOMDisplay.prototype.drawBackground = function() {
    var table = elt('table', 'background');
    table.style.width = this.level.width * scale + 'px';
    this.level.grid.forEach(function(row) {
        var rowElt = table.appendChild(elt('tr'));
        rowElt.style.height = scale + 'px';
        row.forEach(function(type) {
            rowElt.appendChild(elt('td', type));
        });
    });
    return table;
};
// Draw the actors
DOMDisplay.prototype.drawActors = function() {
    var wrap = elt('div');
    this.level.actors.forEach(function(actor) {
        var rect = wrap.appendChild(elt('div', 'actor ' + actor.type));
        rect.style.width  = actor.size.x * scale + 'px';
        rect.style.height = actor.size.y * scale + 'px';
        rect.style.left   = actor.pos.x * scale + 'px';
        rect.style.top    = actor.pos.y * scale + 'px';
    });
    return wrap;
};
// Redraw the actors
DOMDisplay.prototype.drawFrame = function() {
    if (this.actorLayer)
        this.wrap.removeChild(this.actorLayer);
    this.actorLayer = this.wrap.appendChild(this.drawActors());
    // The status class is used to style the player based on
    // the state of the game (won or lost)
    this.wrap.className = 'game ' + (this.level.status || '');
    this.scrollPlayerIntoView();
};
// Make sure the player's always on screen
DOMDisplay.prototype.scrollPlayerIntoView = function() {
    var width = this.wrap.clientWidth;
    var height = this.wrap.clientHeight;
    var margin = width / 3;

    // The viewport
    var left = this.wrap.scrollLeft, right = left + width;
    var top = this.wrap.scrollTop, bottom = top + height;

    // center makes use of the Vector methods defined earlier
    var player = this.level.player;
    var center = player.pos.plus(player.size.times(0.5))
        .times(scale);

    if (center.x < left + margin)
        this.wrap.scrollLeft = center.x - margin;
    else if (center.x > right - margin)
        this.wrap.scrollLeft = center.x + margin - width;
    if (center.y < top + margin)
        this.wrap.scrollTop = center.y - margin;
    else if (center.y > bottom - margin)
        this.wrap.scrollTop = center.y + margin - height;
}
// Clear the level
DOMDisplay.prototype.clear = function() {
    this.wrap.parentNode.removeChild(this.wrap);
};

// Canvas API helper function
function flipHorizontally(context, around) {
    context.translate(around, 0);
    context.scale(-1, 1);
    context.translate(-around, 0);
}
// Use Canvas API to draw game
function CanvasDisplay(parent, level) {
    // Set up the canvas element
    this.canvas = document.createElement('canvas');
    this.canvas.width = Math.min(1000, level.width * scale);
    this.canvas.height = Math.min(1000, level.height * scale);
    this.canvas.style.display = 'block';
    this.canvas.style.margin = '200px auto 0';
    parent.appendChild(this.canvas);
    this.cx = this.canvas.getContext('2d');

    this.level = level;
    // Uses the step size passed to drawFrame()
    this.animationTime = 0;
    this.flipPlayer = false;

    this.viewport = {
        left: 0,
        top: 0,
        width: this.canvas.width / scale,
        height: this.canvas.height / scale
    };

    this.drawFrame(0);
}
CanvasDisplay.prototype.clear = function() {
    this.canvas.parentNode.removeChild(this.canvas);
};
// Draw the frame
CanvasDisplay.prototype.drawFrame = function(step) {
    this.animationTime += step;

    // Update the current player position for the viewport
    this.updateViewport();
    // Clear current frame
    this.clearDisplay();
    // Draw the background
    this.drawBackground();
    // Draw the actors
    this.drawActors();
};
// Scrolls the viewport depending on the player position
CanvasDisplay.prototype.updateViewport = function() {
    var view = this.viewport, margin = view.width / 3;
    var player = this.level.player;
    var center = player.pos.plus(player.size.times(0.5));

    // Compare the center.x of player to the viewport
    // Player is less than the left of the viewport plus margin
    if (center.x < view.left + margin)
        // Scroll left until less than 0
        view.left = Math.max(center.x - margin, 0);
    // Player is further right than the right of the viewport plus margin
    else if (center.x > view.left + view.width - margin)
        // Scroll right until greater than the edge of the level
        view.left = Math.min(center.x + margin - view.width,
            this.level.width - view.width);
    if (center.y < view.top + margin)
        view.top = Math.max(center.y - margin, 0);
    else if (center.y > view.top + view.height - margin)
        view.top = Math.min(center.y + margin - view.height,
            this.level.height - view.height);
};
CanvasDisplay.prototype.clearDisplay = function() {
    if (this.level.status == 'won')
        this.cx.fillStyle = 'rgb(68, 191, 255)';
    else if (this.level.status == 'lost')
        this.cx.fillStyle = 'rgb(44, 136, 214)';
    else
        this.cx.fillStyle = 'rgb(52, 166, 251)';
    this.cx.fillRect(0, 0,
        this.canvas.width, this.canvas.height);
};
var otherSprites = document.createElement('img');
otherSprites.src = 'http://eloquentjavascript.net/img/sprites.png';
// Draw the background
CanvasDisplay.prototype.drawBackground = function() {
    var view = this.viewport;
    var xStart = Math.floor(view.left);
    var xEnd = Math.ceil(view.left + view.width);
    var yStart = Math.floor(view.top);
    var yEnd = Math.ceil(view.top + view.height);

    for (var y = yStart; y < yEnd; y++) {
        for (var x = xStart; x < xEnd; x++) {
            var tile = this.level.grid[y][x];
            if (tile == null) continue;
            var screenX = (x - view.left) * scale;
            var screenY = (y - view.top) * scale;
            var tileX = tile == 'lava' ? scale : 0;
            this.cx.drawImage(otherSprites,
                tileX,   0,       scale, scale,
                screenX, screenY, scale, scale);
        }
    }
};
// Draw the player (called by drawActors())
var playerSprites = document.createElement('img');
playerSprites.src = 'http://eloquentjavascript.net/img/player.png';
var playerXOverlap = 4;
CanvasDisplay.prototype.drawPlayer = function(x, y, width, height) {
    var sprite = 8, player = this.level.player;
    width += playerXOverlap * 2;
    x -= playerXOverlap;
    if (player.speed.x != 0)
        this.flipPlayer = player.speed.x < 0;

    if (player.speed.y != 0)
        sprite = 9;
    else if (player.speed.x != 0)
        sprite = Math.floor(this.animationTime * 12) % 8;

    this.cx.save();
    if (this.flipPlayer)
        flipHorizontally(this.cx, x + width / 2);

    this.cx.drawImage(playerSprites,
        sprite * width, 0, width, height,
        x,              y, width, height);
    this.cx.restore();
}
// Draw the actors
CanvasDisplay.prototype.drawActors = function() {
    this.level.actors.forEach(function(actor) {
        var width = actor.size.x * scale;
        var height = actor.size.y * scale;
        var x = (actor.pos.x - this.viewport.left) * scale;
        var y = (actor.pos.y - this.viewport.top) * scale;
        if (actor.type == 'player') {
            this.drawPlayer(x, y, width, height);
        } else {
            var tileX = (actor.type == 'coin' ? 2 : 1) * scale;
            this.cx.drawImage(otherSprites,
                tileX, 0, width, height,
                x,     y, width, height);
        }
    }, this);
};


// Run game with DOMDisplay
// runGame(GAME_LEVELS, DOMDisplay);

// Run game with CanvasDisplay
runGame(GAME_LEVELS, CanvasDisplay);

</script>

</body>

</html>

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