javascript ImageData类型数组读取整个像素？ [英] javascript ImageData typed array read whole pixel?

问题描述

因此，有很多关于如何从ImageData对象的Uint32Array视图中写入整个像素的例子。但是是否可以读取整个像素而不增加计数器4次？从 hacks.mozilla.org ，编写rgba像素看起来像 this

So there is are a lot of examples on how to write an entire pixel from a Uint32Array view of the ImageData object. But is it possible to read an entire pixel without incrementing the counter 4 times? From hacks.mozilla.org, writing an rgba pixels looks like this.

var imageData = ctx.getImageData(0, 0, canvasWidth, canvasHeight);

var buf = new ArrayBuffer(imageData.data.length);
var buf8 = new Uint8ClampedArray(buf);
var data = new Uint32Array(buf);

for (var y = 0; y < canvasHeight; ++y) {
    for (var x = 0; x < canvasWidth; ++x) {
        var value = x * y & 0xff;

        data[y * canvasWidth + x] =
            (255   << 24) |    // alpha
            (value << 16) |    // blue
            (value <<  8) |    // green
             value;            // red
    }
}

imageData.data.set(buf8);

ctx.putImageData(imageData, 0, 0);

但是，如何从ImageData的32位视图中的单个偏移读取整个像素？这里是我发现混乱，下面的 buf32 长度为256/4 = 64？

But, how can I read an entire pixel from a single offset in a 32-bit view of ImageData? Here's what I'm finding confusing, shouldn't the buf32 below have a length of 256/4 = 64?

// 8x8 image
var imgd = ctx.getImageData(0, 0, canvasWidth, canvasHeight),
    buf32 = new Uint32Array(imgd.data);

console.log(imgd.data.length);  // 256
console.log(buf32.length);      // 256  shouldn't this be 256/4 ?

谢谢！

推荐答案

想出来，我需要将缓冲区本身传递给Uint32Array构造函数，而不是另一个BufferView。

figured it out, i need to pass the buffer itself into the Uint32Array constructor, not another BufferView.

var buf32 = new Uint32Array(imgd.data.buffer);
console.log(buf32.length)  // 64 yay!

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