在尝试查找 Canvas 上下文的 putImageData() 方法的文档时，我发现了如下内容：
context.putImageData(imgData,x,y,dirtyX,dirtyY,dirtyWidth,dirtyHeight);
（来自http://www.w3schools.com/tags/canvas_putimagedata.asp）
根据我读过的文档，x 和 y 是源图像的索引，而dirtyX 和dirtyY 指定目标画布中绘制图像的坐标。然而，正如您将在下面的示例（和 JSFiddle）中看到的那样，调用 putImageData(imgData,x,y) 有效，而 putImageData(imgData, 0, 0, locX, locY) 无效。我不确定为什么。
编辑：
我想我真正的问题是为什么图像的第一行是黑色的，并且只有 7 行，而不是 8 行。图像应该从画布的左上角开始。它们确实从左侧开始（并且有 8 列）。为什么他们不从顶部开始？
答：这是因为当 yLoc 为 0 时，这条线除以 0：
xoff = imgWidth / (yLoc/3);
JSFiddle：
代码：
<html>
<head>
<title>Canvas tutorial</title>
<script type="text/javascript">
var canvas;
var context; // The canvas's 2d context
function setupCanvas()
{
canvas = document.getElementById('myCanvas');
if (canvas.getContext)
{
context = canvas.getContext('2d');
context.fillStyle = "black"; // this is default anyway
context.fillRect(0, 0, canvas.width, canvas.height);
}
}
function init()
{
loadImages();
startGating();
}
var images = new Array();
var gatingTimer;
var curIndex, imgWidth=0, imgHeight;
// Load images
function loadImages()
{
for (n = 1; n <= 16; n++)
{
images[n] = new Image();
images[n].src = "qxsImages/frame" + n + ".png";
// document.body.appendChild(images[n]);
console.log("width = " + images[n].width + ", height = " + images[n].height);
}
curIndex = 1;
imgWidth = images[1].width;
imgHeight = images[1].height;
}
function redrawImages()
{
if (imgWidth == 0)
return;
curIndex++;
if (curIndex > 16)
curIndex = 1;
// To do later: use images[1].width and .height to layout based on image size
for (var x=0; x<8; x++)
{
for (var y=0; y<8; y++)
{
//if (x != 1)
// context.drawImage(images[curIndex], x*150, y*100);
// context.drawImage(images[curIndex], x*150, y*100, imgWidth/2, imgHeight/2); // scale
// else
self.drawCustomImage(x*150, y*100);
}
}
}
function drawCustomImage(xLoc, yLoc)
{
// create a new pixel array
imageData = context.createImageData(imgWidth, imgHeight);
pos = 0; // index position into imagedata array
xoff = imgWidth / (yLoc/3); // offsets to "center"
yoff = imgHeight / 3;
for (y = 0; y < imgHeight; y++)
{
for (x = 0; x < imgWidth; x++)
{
// calculate sine based on distance
x2 = x - xoff;
y2 = y - yoff;
d = Math.sqrt(x2*x2 + y2*y2);
t = Math.sin(d/6.0);
// calculate RGB values based on sine
r = t * 200;
g = 125 + t * 80;
b = 235 + t * 20;
// set red, green, blue, and alpha:
imageData.data[pos++] = Math.max(0,Math.min(255, r));
imageData.data[pos++] = Math.max(0,Math.min(255, g));
imageData.data[pos++] = Math.max(0,Math.min(255, b));
imageData.data[pos++] = 255; // opaque alpha
}
}
// copy the image data back onto the canvas
context.putImageData(imageData, xLoc, yLoc); // Works... kinda
// context.putImageData(imageData, 0, 0, xLoc, yLoc, imgWidth, imgHeight); // Doesn't work. Why?
}
function startGating()
{
gatingTimer = setInterval(redrawImages, 1000/25); // start gating
}
function stopGating()
{
clearInterval(gatingTimer);
}
</script>
<style type="text/css">
canvas { border: 1px solid black; }
</style>
</head>
<body onload="setupCanvas(); init();">
<canvas id="myCanvas" width="1200" height="800"></canvas>
</body>
</html>