Question

以下代码失败且没有错误，它只是不将所有像素保持为绿色。由此产生的噪音效果非常酷，但我希望它们是绿色的。我认为错误是因为我正在复制行但没有将它与RGBA读取帧对齐。小提琴在这里：http://jsfiddle.net/mDk2W/2/

var s = document.getElementById('s');
s.width = 640;
s.height = 480;
var x = s.getContext('2d');
var idata;
var ppx;

function arrayCopy(src, sstart, dst, dstart, length) {
    for (var i = sstart; i < sstart + length; i += 1) {
        dst[dstart++] = src[i];
    }
}

function loadPixels() {
    idata = x.getImageData(0, 0, s.width, s.height);
    ppx = idata.data;
}

function updatePixels() {
    idata.data = ppx;
    x.putImageData(idata, 0, 0);
}

function setup_static() {
    loadPixels();
    for (var y = 0; y < ppx.length - 4; y += 4) {
        var spread = Math.round(Math.random() * 4);
        switch (spread) {
            case (1):
                if (y - 1920 > 0) {
                    ppx[y + 1] = ppx[y - 1919];
                }
                break;
            case (2):
                if (y - 4 > 0) {
                    ppx[y + 1] = ppx[y - 3];
                }
                break;
            case (3):
                ppx[y + 1] = parseInt(Math.round(Math.random()) * 255);
                if (y + 1921 < ppx.length) {
                    ppx[y + 1920] = ppx[y + 1];
                }
                break;
            case (4):
                ppx[y + 1] = parseInt(Math.round(Math.random()) * 255);
                if (y + 5 < ppx.length) {
                    ppx[y + 5] = ppx[y + 1];
                }
                break;
            case (0):
                break;
        };
    }
}
setup_static();
var height = s.height;
var heightover2 = height / 2.0;
var widthby4 = s.width * 4;

function draw() {
    for (y = 0; y < height; y += 1) {
        arrayCopy(ppx, parseInt(Math.round(Math.random() * (heightover2))), ppx, y * widthby4, widthby4);
    }
    updatePixels();
    requestAnimationFrame(draw);
}
draw();

Answer 1

工作小提琴：http://jsfiddle.net/8rgFQ/

以下代码有效且具有4种不同的绘图功能（具有不同级别的feedback）：

var s = document.getElementById('s');
s.width = 640;
s.height = 395;
var height = s.height;
var heightover2 = height/2.0;
var widthby4 = s.width*4;
var x = s.getContext('2d');
var idata;
var ppx,pixels;
function arrayCopy(src,sstart,dst,dstart,length) {
           for(var i = sstart; i < sstart+length;i+=1 ) {
                  dst[dstart++] = src[i];
           }
    }
function fillArray(a,c,l) {
    a = new Array(l);
    while(l-- > 0) {
        a[l] = c;
    }
    return a;
};
function loadPixels() {
    idata = x.getImageData(0,0,s.width,s.height);
    ppx = idata.data;
    idata = x.getImageData(0,0,s.width,s.height);
    pixels = idata.data;
}
function updatePixels() {
    idata.data = pixels;
    x.putImageData(idata,0,0);
}
function setup_static() {
      loadPixels();
      for (var y = 0; y < ppx.length-4;y+=2) {
          var spread = Math.round(Math.random()*4);
          switch(spread) {
        case(1):
            if(y-widthby4+1 > 0) {
            ppx[y+1] = ppx[y-widthby4+1];
            }
            break;
        case(2):
            if(y-4 > 0) {
            ppx[y+1] = ppx[y-3];
            }
            break;
        case(3):
            ppx[y+1] = parseInt(Math.round(Math.random())*255);
            if(y+widthby4+1 < ppx.length) {
            ppx[y+widthby4+1] = ppx[y+1];
            }
            break;
        case(4):
            ppx[y+1] = parseInt(Math.round(Math.random())*255);
            if(y+5 < ppx.length) {
            ppx[y+5] = ppx[y+1];
            }
            break;
        case(0):
            break;
          };
    }
}
setup_static();
//arrayCopy(ppx,0,pixels,0,ppx.length);
//updatePixels();
// height rows of feedback per frame and no reading frame alignment
function draw() {
    for (y = 0; y < height; y += 1) {
        arrayCopy(pixels, parseInt(Math.round(Math.random() * (heightover2))), pixels, y * widthby4, widthby4);
    }
    updatePixels();
    requestAnimationFrame(draw);
}
//arrayCopy(ppx,0,pixels,0,ppx.length);
//draw();
// height rows of feedback per frame
function draw1() {
    for(y = 0; y < height;y+=1) {
        var row = parseInt( Math.round(Math.random()*(heightover2)));
        row -= row%2;
            arrayCopy(pixels,row, pixels, y*widthby4,widthby4);
    }
    updatePixels();
    requestAnimationFrame(draw1);
}
//arrayCopy(ppx,0,pixels,0,ppx.length);
//draw1();
// no feedback beyond 1 frame
function draw2() {
    for(y = 0; y < height;y+=1) {
        var row = parseInt( Math.round(Math.random()*(heightover2)));

        row -= row%2;
            arrayCopy(ppx,row, pixels, y*widthby4,widthby4);
    }
    for(y = 0; y < height;y+=1) {
        var row = parseInt( Math.round(Math.random()*(heightover2)));

        row -= row%2;
            arrayCopy(pixels,row, pixels, y*widthby4,widthby4);
    }
    updatePixels();
    requestAnimationFrame(draw2);
}
//draw2();
// 1 row of feedback per frame
function draw3() {
    for(y = 0; y < height;y+=1) {
        var row = parseInt( Math.round(Math.random()*(heightover2)));

        row -= row%2;
            arrayCopy(ppx,row, pixels, y*widthby4,widthby4);
    }
    for(y = 0; y < height;y+=1) {
        var row = parseInt( Math.round(Math.random()*(heightover2)));

        row -= row%2;
            arrayCopy(pixels,row, pixels, y*widthby4,widthby4);
    }
    var row = parseInt( Math.round(Math.random()*(heightover2)));
    arrayCopy(pixels,row,ppx,row*widthby4,widthby4);
    updatePixels();
    requestAnimationFrame(draw3);
}
draw3();

HTML / CSS：

<style>
#s {
    width:640px;
    height:395px;
    background:black;   
}
</style>
<canvas id="s"></canvas>

JS / canvas putImageData失败

1 个答案: