easeljs - 预加载图像后使用 EaselJS 翻转 SpriteSheet 动画

Question

我正在尝试水平翻转 SpriteSheet 动画中的 Sprite 。我从this example开始

我在创建SpriteSheet后立即添加了翻转的帧

    var ss = new createjs.SpriteSheet(spriteSheet);

    createjs.SpriteSheetUtils.addFlippedFrames(ss, true, false, false);

    grant = new createjs.BitmapAnimation(ss);
...

我总是收到此错误:

Uncaught TypeError: Cannot read property 'length' of null    (SpriteSheetUtils.js l.174)

我发现有人在这个 github thread 中遇到了同样的问题并使用预加载机制修复了它。

该示例也使用预加载，因此我尝试在资源加载后调用 addFlippedFrames，但我仍然看到相同的错误。

有人可以告诉我吗？如何使用 addFlippedFrames ？

编辑:这是我尝试过的代码:

使用我的 Sprite 表初始化舞台:

    spriteSheet = new createjs.SpriteSheet({
        "animations": {
            "none": [0, 0],
            "run": [0, 25],
            "jump": [26, 63]
        },
        "images": ["characters/grant/runningGrant.png"],
        "frames": {
            "height": h,
            "width": w,
            "regX": 0,
            "regY": 0,
            "count": 64
        }
    });



    sprite = new createjs.BitmapAnimation(spriteSheet);
    sprite.x = startPosition.x;
    sprite.y = startPosition.y;

// Add the sprite to the stage.
stage.addChild(this.sprite);

然后像这样使用预加载:

var manifest = [{
        src: "characters/grant/runningGrant.png",
        id: "grant"
    }
];

var loader = new createjs.LoadQueue(false);
loader.onFileLoad = handleFileLoad;
loader.onComplete = onResourcesLoaded;
loader.loadManifest(manifest);

和回调函数:

handleFileLoad = function(event) {
    assets.push(event.item);
};

onResourcesLoaded = function() {

    for (var i = 0; i < assets.length; i++) {
        var item = assets[i];
        var id = item.id;
        var result = loader.getResult(id);

        if (item.type == createjs.LoadQueue.IMAGE) {
            var bmp = new createjs.Bitmap(result);
                //does this Bitmap creation trigger the real bitmap loading ?
                //is this loading asynchrous which would explain my problem.
                //in this case, how can I manage the loading callback ?
        }
    }

    //I would expect here to have the image fully loaded but its not
    //A timeout of 2 seconds makes the addFlippedFrames works.
    setTimeout(function(){
            createjs.SpriteSheetUtils.addFlippedFrames(spriteSheet, true, false, false);
            sprite.gotoAndPlay("run_h"); //I think "run_h" is used to launch the flipped version of "run"
    }, 2000);
};

Answer 1

你的问题是，你创建了一个带有图像url的SpriteSheet，这已经触发了加载过程，而preload-js队列实际上没有加载任何内容，因为图像的加载已经在进行中，所以“onComplete” “-事件总是在图像实际加载之前触发 - 这是有道理的，因为不需要加载图像两次

我更新了你的 jsfiddle 并添加了一些评论:http://jsfiddle.net/K4TmS/1/ (完整代码)

spriteSheet = new createjs.SpriteSheet({
            "animations": {
                "none": [0, 0],
                "run": [0, 25],
                "jump": [26, 63]
            },
            //this line in YOUR version triggered an own loading process, independent from the queue
            "images": [result],  
            "frames": {
                "height": 292.5,
                "width":165.75,
                "regX": 0,
                "regY": 0,
                "count": 64
            }
        });

// this was executed instantly, because the image was already in another loading progress, and therefore wasn't even added to the queue
loader.onComplete = onResourcesLoaded;

可以使用此参数忽略 DOM 安全错误18(用于开发)Disable same origin policy in Chrome但对于生产环境，您应该只从同一服务器加载 img，然后图像操作就不会给出错误。

简而言之:您的问题是由于执行顺序错误造成的，请记住:如果您使用预加载:在执行其他操作之前进行预加载，并且在预加载完成之前不执行任何其他操作。 (加载图形/动画/指示器除外)。