为什么每次精灵移动时我的地图都会消失

jsFiddle：https://jsfiddle.net/j353agny/3/

var canvas = document.getElementById('myCanvas');
var context = canvas.getContext("2d");
var mapArray = ["############################",
    "#      #    #      o      ##",
    "#                          #",
    "#   ####   #####    ##     #",
    "##         #   #    ##     #",
    "###           ##     #     #",
    "#           ###      #     #",
    "#   ####          ###      #",
    "#   ##    #  o             #",
    "# o  #    #    o ###   ### #",
    "#    #    #                #",
    "############################"];
//need to add wall.scource =  and grass.source =
var wall = new Image();
var grass = new Image();
grass.src = "http://vignette2.wikia.nocookie.net/tibia/images/6/60/Grass_(Tile).gif/revision/latest?cb=20080817072800&path-prefix=en";
wall.src = "data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wCEAAkGBwgHBgkIBwgKCgkLDRYPDQwMDRsUFRAWIB0iIiAdHx8kKDQsJCYxJyofLT0tMSw3QTo6LC87RD84Nzc5OjcBCgoKBQUFDgUFDisZExkrKysrKysrKysrKysrKysrKysrKysrKysrKysrKysrKysrKysrKysrKysrKysrKysrK//AABEIACAAIAMBIgACEQEDEQH/xAAYAAADAQEAAAAAAAAAAAAAAAACAwQFAP/EACkQAAEDAwIDCQEAAAAAAAAAAAECAxEABCESEyMxURQyM0Fhc4GT0QX/xAAUAQEAAAAAAAAAAAAAAAAAAAAA/8QAFBEBAAAAAAAAAAAAAAAAAAAAAP/aAAwDAQACEQMRAD8Au/oXDzT2ltZSJxAHKp27242yC5nPxQ3Qm5dVqzOMelI7vNMdYoKm718Jw4c85ApN5cXIbWvdUTtk48qBKkGcgEdaFRT2e4AIPCVQaF+1tvuawAVEQKlVBM8ulHfPoXeunfaKQqJ1ilrW0UnjNfYP2gVoCoURIpdwhoMuhKTG2ZNODiJI3miPcFddvMm1cSHGvDIEKBJoP//Z";
// Player position
var posX = 0;
var posY = 0;
//moves character
function move(e) {
    //alert(e.keyCode);//gives feedback to what each keyCode is
    if (e.keyCode == 39) {
        posX += 5;
    }
    if (e.keyCode == 37) {
        posX -= 5;
    }
    if (e.keyCode == 40) {
        posY += 5;
    }
    if (e.keyCode == 38) {
        posY -= 5;
    }
}
document.onkeydown = move;
// every 3 miliseconds re-draw the stage with the player
setInterval(function () {
    console.log("REDRAW");
    // Clear the canvas and redraw
    context.fillStyle = "#FFF";
    context.fillRect(0,0,800,600);
    //for loops set images at given coordinates according to position on mapArray
    for (var y = 0; y < mapArray.length; y++) {
        for (var x = 0; x < mapArray[0].length; x++) {
            if (mapArray[y][x] == "") {
                context.drawImage(grass, (32 * x), (32 * y), 32, 32) //last two are size of image )
            }
            if (mapArray[y][x] == "#") {
                context.drawImage(wall, (32 * x), (32 * y), 32, 32) //last two are size of image )
            }
        }
    }
    context.fillStyle = "#00F";
    context.fillRect(posX, posY, 32, 32)
}, 3);

您所能做的就是使用setInterval，它将每3毫秒运行一次。基本上每3毫秒，我就会得到画布来重新绘制你的墙，然后重新绘制玩家。这将停止任何奇怪的绘图问题。

请注意，您可以使用requestAnimationFrame而不是setInterval，只是为了让您知道

是的，您的canvas.width = canvas.width;将清除画布，移动后您将只得到rect。也可以在move函数中执行所有渲染代码，或者为地图提供一个备份画布，以便在move功能的顶部高效地渲染它，而无需每次都遍历mapArray。在这里，他们使用备份画布：html5：将画布复制到图像并返回

基于备份画布思想的代码：

var canvas = <HTMLCanvasElement>document.getElementById('myCanvas');
var context = canvas.getContext("2d");
var img = new Image();
img.onload = function () {
    context.drawImage(img, 0, 0);
}
img.src = "";

var mapArray =
       ["############################",
        "#      #    #      o      ##",
        "#                          #",
        "#   ####   #####    ##     #",
        "##         #   #    ##     #",
        "###           ##     #     #",
        "#           ###      #     #",
        "#   ####          ###      #",
        "#   ##    #  o             #",
        "# o  #    #    o ###   ### #",
        "#    #    #                #",
        "############################"];
//need to add wall.scource =  and grass.source =
var wall = new Image();
var grass = new Image();
grass.src = "http://vignette2.wikia.nocookie.net/tibia/images/6/60/Grass_(Tile).gif/revision/latest?cb=20080817072800&path-prefix=en";
wall.src = "data:image/jpeg;base64,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";

var posX = 0;
var posY = 0;


//for loops set images at given coordinates according to position on mapArray
for (var y = 0; y < mapArray.length; y++) {
    for (var x = 0; x < mapArray[0].length; x++) {
        if (mapArray[y][x] == "") {
            context.drawImage(grass, (32 * x), (32 * y), 32, 32)//last two are size of image )
        }
        if (mapArray[y][x] == "#") {
            context.drawImage(wall, (32 * x), (32 * y), 32, 32)//last two are size of image )
        }
 }
}
// Here you've rendered the static content and you want to save the state of the canvas in a backup at this point:
// create backing canvas
var backCanvas = document.createElement('canvas');
backCanvas.width = canvas.width;
backCanvas.height = canvas.height;
var backCtx = backCanvas.getContext('2d');
// save main canvas contents
backCtx.drawImage(canvas, 0,0);
context.rect(posX, posY, 32, 32)
context.stroke();//traces path, might not need this

//moves character
function move(e) {
    canvas.width = canvas.width;//clears the board after each move (not really necessary since we'll draw the backCanvas over it...)
    // Render the backup canvas here
    context.drawImage(backCanvas, 0,0);
    //alert(e.keyCode);//gives feedback to what each keyCode is
    if (e.keyCode == 39) {
        posX += 5;
    }
    if (e.keyCode == 37) {
        posX -= 5;
    }
    if (e.keyCode == 40) {
        posY += 5;
    }
    if (e.keyCode == 38) {
        posY -= 5;
    }
    context.rect(posX, posY, 32, 32)
    context.stroke();
}    
document.onkeydown = move;