如何用箭头键在画布html5上移动图像？

Question

I saw many peps with same question but none of the solution helped me ..so i post the question. 我看到许多鼓舞人心的问题，但没有一个解决方案帮助我..所以我发布了问题。 I want to move my second pic "g_fighter.png" over the background . 我想将第二张图片“ g_fighter.png”移到背景上。 so i wrote the codes now its draw the images over the canvas but on keypress the pic dont move ! 所以我现在写了代码，它在画布上绘制图像，但是在按键时图片不会移动！ It will be very helpfull if anyone can find the flaw in my code ` 如果有人可以在我的代码中找到缺陷，这将非常有帮助。

<html>
<body onload=start()>
<center>
<canvas id="myCanvas" width="500" height="500" style="border:1px solid #000000;">Your browser does not support canvas tag.</canvas>
</center>
<script>
//Background Image 
var bgReady = false;
var bgImage = new Image();
bgImage.onload = function(){
    bgReady = true;
}
bgImage.src="img/heic0706a.jpg";

//Friend Image
var fReady = false; 
var fImage = new Image();
fImage.onload = function(){
      fReady = true;
}
fImage.src="img/g_fighter.png";

//Game objects
var hero = {
     speed:1,
     x:200,
     y:390
};

var keysDown = {};
addEventListener("keydown", function(e){
        keysDown[e.keyCode] = true;
}, false);
addEventListener("keyup", function(e){
        delete keysDown[e.keyCode];
}, false);


function update(modifier){

    if(38 in keysDown){
        hero.y -= hero.speed * modifier;
    }
    if(40 in keysDown){
        hero.y += hero.speed * modifier;
    }
    if(37 in keysDown){
        hero.x -= hero.speed * modifier;
    }
    if(39 in keysDown){
        hero.x += hero.speed * modifier;
    }
}

function render(c){
    if(bgReady == true){
        c.drawImage(bgImage,0,0);
    }
    if(fReady == true){
        c.drawImage(fImage,hero.x,hero.y,100,100);
    }
}
function setImage(then){
    var canvas = document.getElementById("myCanvas");
    var ctx = canvas.getContext("2d");
    var now = Date.now();
    var delta = now-then;

    update(delta/1000);
    render(ctx);

    then = now;

    requestAnimationFrame(setImage);
}
    var w = window;
    requestAnimationFrame = w.requestAnimationFrame || w.webkitRequestAnimationFrame || w.msRequestAnimationFrame || w.mozRequestAnimationFrame;

function start(){
    var Then = Date.now();
    setImage(Then);
}

</script>
</body>
</html>

` `

Answer 1

look a fiddle i set up: 看我设置的小提琴：

http://jsfiddle.net/7fsw81mp/14/ http://jsfiddle.net/7fsw81mp/14/

function render(c){
    c.clearRect(0,0,600,600)
    if(fReady == true){
        c.drawImage(fImage,hero.x,hero.y,100,100);
    }
}

First of all I cannot see where were you calling the start function. 首先，我看不到您在哪里调用start函数。

I put the then parameter as an external var, so i do not need to pass trought every requestAnimationFrame, i'm not sure if it goes as a parameter otherwise 我把then参数作为一个外部变量，所以我不需要传递所有的requestAnimationFrame，我不确定是否将其作为参数

Then the speed was very slow, 1 pixel per second, means that it barely moved 然后速度非常慢，每秒1像素，这意味着它几乎没有移动

Also you have to clear the canvas every render, otherwise your hero will leave a trail behind him. 另外，您必须在每次渲染时清除画布，否则您的英雄将在他身后留下痕迹。

full snippet: 完整摘要：

 //Friend Image var fReady = false; var fImage = new Image(); fImage.onload = function(){ fReady = true; } fImage.src="http://vignette1.wikia.nocookie.net/finalfantasy/images/0/0a/FFTS_Fighter_Sprite.png"; var then = 0; //Game objects var hero = { speed:10, x:200, y:390 }; var keysDown = {}; addEventListener("keydown", function(e){ keysDown[e.keyCode] = true; e.preventDefault(); }, false); addEventListener("keyup", function(e){ delete keysDown[e.keyCode]; e.preventDefault(); }, false); function update(modifier){ if(38 in keysDown){ hero.y -= hero.speed * modifier; } if(40 in keysDown){ hero.y += hero.speed * modifier; } if(37 in keysDown){ hero.x -= hero.speed * modifier; } if(39 in keysDown){ hero.x += hero.speed * modifier; } } function render(c){ c.clearRect(0,0,600,600) if(fReady == true){ c.drawImage(fImage,hero.x,hero.y,100,100); } } function setImage(){ var canvas = document.getElementById("myCanvas"); var ctx = canvas.getContext("2d"); var now = Date.now(); var delta = now-then; update(delta/1000); render(ctx); then = now; requestAnimationFrame(setImage); } var w = window; requestAnimationFrame = w.requestAnimationFrame || w.webkitRequestAnimationFrame || w.msRequestAnimationFrame || w.mozRequestAnimationFrame; function start(){ console.log('starting'); then = Date.now(); setImage(); } start();

 <canvas id="myCanvas" width="600" height="600"></canvas>

如何用箭头键在画布html5上移动图像？

问题描述

1 个解决方案

解决方案1
1 已采纳 2015-11-29 11:39:46

如何用箭头键在画布html5上移动图像？

问题描述

1 个解决方案

解决方案1 1 已采纳 2015-11-29 11:39:46

解决方案1
1 已采纳 2015-11-29 11:39:46