检测径向像素

Question

我不想检查径向元素的碰撞。

问题是，目前我只检查矩形的像素，因为其他图像是原生的 HTML-Elements。

我只是用canvas绘制边界背景来检查alpha-transparency。

this.checkCollision = function checkCollision() {
    var width   = 34;
    var height  = 32;
    var image   = _context.getImageData(_position.x - (height / 2), _position.y - (width / 2), width, height);
    var pixels  = image.data;
    var size    = image.data.length;

    // HERE I WANT TO CHECK A RADIAL AREA
    for(var index = 0; index < size; index += 4) {
        var RED     = image.data[index];
        var GREEN   = image.data[index + 1];
        var BLUE    = image.data[index + 2];
        var ALPHA   = image.data[index + 3];

        if(_debug) {
            document.querySelector('#debug').innerHTML = JSON.stringify({
                POSITION:   _position,
                INDEX:      index,
                COLOR: {
                    R:  RED,
                    G:  GREEN,
                    B:  BLUE,
                    A:  ALPHA
                }
            }, 0, 1);
        }

        if(ALPHA !== 0) {
            return true;
        }
    }
    _context.putImageData(image, 0, 0);
    return false;
};

预览

这是一个有效的 Fiddle:

https://jsfiddle.net/2bLfd6xp/

我如何 select getImageData 上的径向像素范围来检查与 boundary.png 中的 alpha-transparency 的碰撞？

我的想法是从这里修改像素数据数组：

var image   = _context.getImageData(_position.x - (height / 2), _position.y - (width / 2), width, height);

并删除不可见的 edges。但是，从基于矩形的像素阵列计算径向区域以移除这些不需要的像素的最佳做法是什么？

示例：

var image   = _context.getImageData(_position.x - (height / 2), _position.y - (width / 2), width, height);

var radial_area = selectRadialArea(image, radius);

function selectRadialArea(pixelArray, radius) {
   /*
      Modify `pixelArray` with given `radius`...
      All pixels outside the `radius`  filled with `null`...
   */
   return theNewArray;
}

Answer 1

我用逻辑思维找到了答案：

首先，我们创建一个临时的可绘制上下文并在这个新区域中绘制两个元素：

一个红色矩形
具有目的地-复合

结果 Uint8ClampedArray 将 与原始 Uint8ClampedArray 进行比较。如果区域是 RED，我们用 null-entries:

隐藏像素

this.rectangleToRadial = function rectangleToRadial(source, width, height) {
    var test        = document.createElement('canvas');
    var context     = test.getContext('2d');

    // Create an transparent circle and a red removeable area
    context.beginPath();
    context.fillStyle = 'rgba(255, 0, 0, 1)';
    context.fillRect(0, 0, width, height);
    context.globalCompositeOperation = 'destination-out';
    context.arc(width / 2, height / 2, width / 2, 0, 2 * Math.PI);
    context.fillStyle = 'rgba(0, 0, 0, 1)';
    context.fill();

    // get the data
    var destination = context.getImageData(0, 0, width, height);
    var size        = destination.data.length;

    // check the pixels
    for(var index = 0; index < size; index += 4) {
        var RED     = destination.data[index];
        var GREEN   = destination.data[index + 1];
        var BLUE    = destination.data[index + 2];
        var ALPHA   = destination.data[index + 3];

        /*
            if the >>red removeable area<< is given, null the pixel from the source
        */
        if(RED == 255 && GREEN == 0 && BLUE == 0) {
            // Remove this from source
            source.data[index]      = null;
            source.data[index + 1]  = null;
            source.data[index + 2]  = null;
            source.data[index + 3]  = null;
        }
    }

    // Return the source `Uint8ClampedArray`
    return source;
};

这很容易，当我们试着思考时:)

    var image   = _context.getImageData(_position.x - (height / 2), _position.y - (width / 2), width, height);
    var pixels  = this.rectangleToRadial(image, width, height);

检测径向像素

Detect radial Pixel

javascript

collision-detection

getimagedata

radial