如何创建一个在画布上绘制精灵的函数?

时间:2017-03-12 21:43:55

标签: javascript html5 canvas html5-canvas

我需要在sprite()中使用canvas创建函数javascript 我有2个代码 这个来创建一个精灵:

var width = 40,
    height = 28,
    frames = 2,

    currentFrame = 0,

    canvas = document.getElementById("myCanvas");
    ctx = canvas.getContext("2d");
    image = new Image()
    image.src = 'http://s28.postimg.org/k90gybbtl/bird_Sprite.png';

var draw = function(){
    ctx.clearRect(0, 0, width, height);
    ctx.drawImage(image, 0, height * currentFrame, width, height, 0, 0, width, height);

    if (currentFrame == frames) {
      currentFrame = 0;
    } else {
      currentFrame++;
    }
}

setInterval(draw, 120);

我还有另一个简单游戏的代码:

function startGame() {
    myGamePiece = new component(30, 30, "red", 10, 120);
    myGamePiece.gravity = 0.05;
    myScore = new component("30px", "Consolas", "black", 280, 40, "text");
    myUpBtn = new component(canvasWidth, canvasHeight, "rgba(0, 0, 0, 0)", 0, 0); 
    myGameArea.start();
}

function component(width, height, color, x, y, type) {
    this.type = type;
    if (type == "image") {
      this.image = new Image();
      this.image.src = color;
    }
    this.score = 0;
    this.width = width;
    this.height = height;
    this.speedX = 0;
    this.speedY = 0;    
    this.x = x;
    this.y = y;
    this.gravity = 0;
    this.gravitySpeed = 0;
    this.update = function() {
        ctx = myGameArea.context;
        if (this.type == "text") {
            ctx.font = this.width + " " + this.height;
            ctx.fillStyle = color;
            ctx.fillText(this.text, this.x, this.y);
        } else {
                if (type == "image") {
                    ctx.drawImage(this.image, 
                    this.x, 
                    this.y,
                    this.width, this.height);
                } else {
            ctx.fillStyle = color;
            ctx.fillRect(this.x, this.y, this.width, this.height);
            }
        }
    }
        this.clicked = function() {
        var mytop = this.y;

        var clicked = true;
        if (mytop > myGameArea.y) {
            clicked = false;
        }
        return clicked;
    }
    this.newPos = function() {
        this.gravitySpeed += this.gravity;
        this.x += this.speedX;
        this.y += this.speedY + this.gravitySpeed;
        this.hitBottom();
    }
    this.hitBottom = function() {
        var rockbottom = myGameArea.canvas.height - this.height;
        if (this.y > rockbottom) {
            this.y = rockbottom;
            this.gravitySpeed = 0;
        }
    }
    this.crashWith = function(otherobj) {
        var myleft = this.x;
        var myright = this.x + (this.width);
        var mytop = this.y;
        var mybottom = this.y + (this.height);
        var otherleft = otherobj.x;
        var otherright = otherobj.x + (otherobj.width);
        var othertop = otherobj.y;
        var otherbottom = otherobj.y + (otherobj.height);
        var crash = true;
        if ((mybottom < othertop) || (mytop > otherbottom) || (myright < otherleft) || (myleft > otherright)) {
            crash = false;
        }
        return crash;
    }
} // https://www.w3schools.com/graphics/game_images.asp

...等 现在问题是......

我无法将2个代码组合在一起

任何人都可以帮助我吗?

谢谢你:)

1 个答案:

答案 0 :(得分:0)

以下代码将您的精灵添加到W3 Schools的游戏代码中:

&#13;
&#13;
var myGamePiece;
var myObstacles = [];
var myScore;

function startGame() {
    myGamePiece = new component(40, 28, "red", 10, 120, "sprite");
    myGamePiece.gravity = 0.05;
    myScore = new component("30px", "Consolas", "black", 280, 40, "text");
    myGameArea.start();
}

var myGameArea = {
    canvas : document.createElement("canvas"),
    start : function() {
        this.canvas.width = 480;
        this.canvas.height = 270;
        this.context = this.canvas.getContext("2d");
        document.body.insertBefore(this.canvas, document.body.childNodes[0]);
        this.frameNo = 0;
        this.interval = setInterval(updateGameArea, 20);
        },
    clear : function() {
        this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
    }
}

function component(width, height, color, x, y, type) {
    this.type = type;
    this.score = 0;
    this.width = width;
    this.height = height;
    this.speedX = 0;
    this.speedY = 0;    
    this.x = x;
    this.y = y;
    this.gravity = 0;
    this.gravitySpeed = 0;

    if (type === "sprite") {
        this.currentFrame = 0;
        this.frames = 2;
        this.tickCount = 0;
        this.ticksPerFrame = 4;
        this.image = new Image();
        this.image.src = 'http://s28.postimg.org/k90gybbtl/bird_Sprite.png';
    }

    this.update = function() {
        ctx = myGameArea.context;
        if (this.type == "text") {
            ctx.font = this.width + " " + this.height;
            ctx.fillStyle = color;
            ctx.fillText(this.text, this.x, this.y);
        } else if (this.type == "sprite") {
            if (this.tickCount > this.ticksPerFrame) {
                ctx.drawImage(this.image, 0, this.height * this.currentFrame, this.width, this.height, this.x, this.y, this.width, this.height);

                this.tickCount = 0;

                if (this.currentFrame == this.frames) {
                    this.currentFrame = 0;
                } else {
                    this.currentFrame++;
                }
            } else {
                ctx.drawImage(this.image, 0, this.height * this.currentFrame, this.width, this.height, this.x, this.y, this.width, this.height);
                this.tickCount++;
            }
        } else {
            ctx.fillStyle = color;
            ctx.fillRect(this.x, this.y, this.width, this.height);
        }
    }
    this.newPos = function() {
        this.gravitySpeed += this.gravity;
        this.x += this.speedX;
        this.y += this.speedY + this.gravitySpeed;
        this.hitBottom();
    }
    this.hitBottom = function() {
        var rockbottom = myGameArea.canvas.height - this.height;
        if (this.y > rockbottom) {
            this.y = rockbottom;
            this.gravitySpeed = 0;
        }
    }
    this.crashWith = function(otherobj) {
        var myleft = this.x;
        var myright = this.x + (this.width);
        var mytop = this.y;
        var mybottom = this.y + (this.height);
        var otherleft = otherobj.x;
        var otherright = otherobj.x + (otherobj.width);
        var othertop = otherobj.y;
        var otherbottom = otherobj.y + (otherobj.height);
        var crash = true;
        if ((mybottom < othertop) || (mytop > otherbottom) || (myright < otherleft) || (myleft > otherright)) {
            crash = false;
        }
        return crash;
    }
}

function updateGameArea() {
    var x, height, gap, minHeight, maxHeight, minGap, maxGap;
    for (i = 0; i < myObstacles.length; i += 1) {
        if (myGamePiece.crashWith(myObstacles[i])) {
            return;
        } 
    }
    myGameArea.clear();
    myGameArea.frameNo += 1;
    if (myGameArea.frameNo == 1 || everyinterval(150)) {
        x = myGameArea.canvas.width;
        minHeight = 20;
        maxHeight = 200;
        height = Math.floor(Math.random()*(maxHeight-minHeight+1)+minHeight);
        minGap = 50;
        maxGap = 200;
        gap = Math.floor(Math.random()*(maxGap-minGap+1)+minGap);
        myObstacles.push(new component(10, height, "green", x, 0));
        myObstacles.push(new component(10, x - height - gap, "green", x, height + gap));
    }
    for (i = 0; i < myObstacles.length; i += 1) {
        myObstacles[i].x += -1;
        myObstacles[i].update();
    }
    myScore.text="SCORE: " + myGameArea.frameNo;
    myScore.update();
    myGamePiece.newPos();
    myGamePiece.update();
}

function everyinterval(n) {
    if ((myGameArea.frameNo / n) % 1 == 0) {return true;}
    return false;
}

function accelerate(n) {
    myGamePiece.gravity = n;
}
&#13;
canvas {
    border:1px solid #d3d3d3;
    background-color: #f1f1f1;
}
&#13;
<body onload="startGame()">
  <br>
  <button onmousedown="accelerate(-0.2)" onmouseup="accelerate(0.05)">ACCELERATE</button>
  <p>Use the ACCELERATE button to stay in the air</p>
  <p>How long can you stay alive?</p>
</body>
&#13;
&#13;
&#13;

总结:

  • component函数中,如果type参数设置为sprite
  • ,我们会初始化变量以处理精灵动画
  • update函数中,我们每隔4次调用精灵动画的下一帧update。这可以确保精灵动画不会快速播放
  • 然后我们按照原始代码中的currentFrame计数递增或重置component计数
  • 如果我们还没有准备好在精灵动画中显示下一帧,我们只会再次显示现有的帧。

为了更进一步,您可能需要考虑重构我的解决方案,以便精灵是一个单独的&#34;类&#34;它继承了If的核心功能。