在HTML5画布中设置单个像素的最佳方法是什么?

HTML5 Canvas没有显式设置单个像素的方法。

可以使用非常短的行设置像素，但反字符和行大写可能会干扰。

另一种方法可能是创建一个小的ImageData对象，并使用:

context.putImageData(data, x, y)

把它放在合适的位置。

有人能描述一种高效可靠的方法吗?

当前回答

我没有考虑过fillRect()，但答案促使我对putImage()进行基准测试。

在(旧的)MacBook Pro上使用Chrome 9.0.597.84在随机位置放置100,000个随机颜色的像素，使用putImage()只需不到100毫秒，但使用fillRect()需要近900毫秒。(基准代码在http://pastebin.com/4ijVKJcC)。

如果我在循环之外选择一种颜色，并在随机位置绘制该颜色，putImage()需要59ms而fillRect()需要102ms。

在rgb(…)语法中生成和解析CSS颜色规范的开销似乎是造成大部分差异的原因。

另一方面，将原始RGB值直接放入ImageData块中不需要字符串处理或解析。

2011-02-04 18:30:55

其他回答

长方形呢?这比创建ImageData对象更有效。

2011-02-04 16:35:37

一种没有提到的方法是使用getImageData，然后使用putImageData。这种方法很适合当你想要画很多的时候，快速。 http://next.plnkr.co/edit/mfNyalsAR2MWkccr

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
var canvasWidth = canvas.width;
var canvasHeight = canvas.height;
ctx.clearRect(0, 0, canvasWidth, canvasHeight);
var id = ctx.getImageData(0, 0, canvasWidth, canvasHeight);
var pixels = id.data;

var x = Math.floor(Math.random() * canvasWidth);
var y = Math.floor(Math.random() * canvasHeight);
var r = Math.floor(Math.random() * 256);
var g = Math.floor(Math.random() * 256);
var b = Math.floor(Math.random() * 256);
var off = (y * id.width + x) * 4;
pixels[off] = r;
pixels[off + 1] = g;
pixels[off + 2] = b;
pixels[off + 3] = 255;

ctx.putImageData(id, 0, 0);

2018-07-08 10:33:58

像sdleihssirhc说的那样画一个矩形!

ctx.fillRect (10, 10, 1, 1);

^——应该在x:10, y:10处画一个1x1的矩形

2011-02-04 16:45:07

快速HTML演示代码: 基于我对SFML c++图形库的了解:

将其保存为UTF-8编码的HTML文件并运行。可以随意重构，我只是喜欢用日文变量，因为它们简洁明了，不占太多空间

你很少会想要设置一个任意像素和显示它在屏幕上。所以使用

PutPix(x,y, r,g,b,a)

方法将大量任意像素绘制到后缓冲区。(便宜的调用)

当准备好展示的时候，打电话给

Apply()

方法显示更改。(昂贵的)

完整的。html文件代码如下:

<!DOCTYPE HTML >
<html lang="en">
<head>
    <title> back-buffer demo </title>
</head>
<body>

</body>

<script>
//Main function to execute once 
//all script is loaded:
function main(){

    //Create a canvas:
    var canvas;
    canvas = attachCanvasToDom();

    //Do the pixel setting test:
    var test_type = FAST_TEST;
    backBufferTest(canvas, test_type);
}

//Constants:
var SLOW_TEST = 1;
var FAST_TEST = 2;


function attachCanvasToDom(){
    //Canvas Creation:
    //cccccccccccccccccccccccccccccccccccccccccc//
    //Create Canvas and append to body:
    var can = document.createElement('canvas');
    document.body.appendChild(can);

    //Make canvas non-zero in size, 
    //so we can see it:
    can.width = 800;
    can.height= 600;

    //Get the context, fill canvas to get visual:
    var ctx = can.getContext("2d");
    ctx.fillStyle = "rgba(0, 0, 200, 0.5)";
    ctx.fillRect(0,0,can.width-1, can.height-1);
    //cccccccccccccccccccccccccccccccccccccccccc//

    //Return the canvas that was created:
    return can;
}

//THIS OBJECT IS SLOOOOOWW!
// 筆 == "pen"
//T筆 == "Type:Pen"
function T筆(canvas){


    //Publicly Exposed Functions
    //PEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPE//
    this.PutPix = _putPix;
    //PEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPE//

    if(!canvas){
        throw("[NilCanvasGivenToPenConstruct]");
    }

    var _ctx = canvas.getContext("2d");

    //Pixel Setting Test:
    // only do this once per page
    //絵  =="image"
    //資  =="data"
    //絵資=="image data"
    //筆  =="pen"
    var _絵資 = _ctx.createImageData(1,1); 
    // only do this once per page
    var _筆  = _絵資.data;   


    function _putPix(x,y,  r,g,b,a){
        _筆[0]   = r;
        _筆[1]   = g;
        _筆[2]   = b;
        _筆[3]   = a;
        _ctx.putImageData( _絵資, x, y );  
    }
}

//Back-buffer object, for fast pixel setting:
//尻 =="butt,rear" using to mean "back-buffer"
//T尻=="type: back-buffer"
function T尻(canvas){

    //Publicly Exposed Functions
    //PEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPE//
    this.PutPix = _putPix;
    this.Apply  = _apply;
    //PEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPEPE//

    if(!canvas){
        throw("[NilCanvasGivenToPenConstruct]");
    }

    var _can = canvas;
    var _ctx = canvas.getContext("2d");

    //Pixel Setting Test:
    // only do this once per page
    //絵  =="image"
    //資  =="data"
    //絵資=="image data"
    //筆  =="pen"
    var _w = _can.width;
    var _h = _can.height;
    var _絵資 = _ctx.createImageData(_w,_h); 
    // only do this once per page
    var _筆  = _絵資.data;   


    function _putPix(x,y,  r,g,b,a){

        //Convert XY to index:
        var dex = ( (y*4) *_w) + (x*4);

        _筆[dex+0]   = r;
        _筆[dex+1]   = g;
        _筆[dex+2]   = b;
        _筆[dex+3]   = a;

    }

    function _apply(){
        _ctx.putImageData( _絵資, 0,0 );  
    }

}

function backBufferTest(canvas_input, test_type){
    var can = canvas_input; //shorthand var.

    if(test_type==SLOW_TEST){
        var t筆 = new T筆( can );

        //Iterate over entire canvas, 
        //and set pixels:
        var x0 = 0;
        var x1 = can.width - 1;

        var y0 = 0;
        var y1 = can.height -1;

        for(var x = x0; x <= x1; x++){
        for(var y = y0; y <= y1; y++){
            t筆.PutPix(
                x,y, 
                x%256, y%256,(x+y)%256, 255
            );
        }}//next X/Y

    }else
    if(test_type==FAST_TEST){
        var t尻 = new T尻( can );

        //Iterate over entire canvas, 
        //and set pixels:
        var x0 = 0;
        var x1 = can.width - 1;

        var y0 = 0;
        var y1 = can.height -1;

        for(var x = x0; x <= x1; x++){
        for(var y = y0; y <= y1; y++){
            t尻.PutPix(
                x,y, 
                x%256, y%256,(x+y)%256, 255
            );
        }}//next X/Y

        //When done setting arbitrary pixels,
        //use the apply method to show them 
        //on screen:
        t尻.Apply();

    }
}


main();
</script>
</html>

2017-06-05 21:51:05

嗯，你也可以只做一个1像素宽的线，长度为1像素，让它的方向沿着一个轴移动。

            ctx.beginPath();
            ctx.lineWidth = 1; // one pixel wide
            ctx.strokeStyle = rgba(...);
            ctx.moveTo(50,25); // positioned at 50,25
            ctx.lineTo(51,25); // one pixel long
            ctx.stroke();

2013-03-14 11:33:58

在HTML5画布中设置单个像素的最佳方法是什么?

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