/*
* @param canvas 要处理的画布
*/
cropSignatureCanvas: function(canvas) {
// 复制画布 避免影响之前的画布
var croppedCanvas = document.createElement('canvas'),
croppedCtx = croppedCanvas.getContext('2d');
croppedCanvas.width = canvas.width;
croppedCanvas.height = canvas.height;
croppedCtx.drawImage(canvas, 0, 0);
// 处理画布空白
var w = croppedCanvas.width,
h = croppedCanvas.height,
pix = {x:[], y:[]},
imageData = croppedCtx.getImageData(0,0,croppedCanvas.width,croppedCanvas.height), // 获取canvas像素数据
x, y, index;
for (y = 0; y < h; y++) {
for (x = 0; x < w; x++) {
index = (y * w + x) * 4 + 3; //根据行、列读取某像素点的R/G/B/A值的公式：
if (imageData.data[index] > 0) {
pix.x.push(x);
pix.y.push(y);
}
}
}
pix.x.sort(function(a,b){return a-b});
pix.y.sort(function(a,b){return a-b});
var n = pix.x.length-1;
w = pix.x[n] - pix.x[0];
h = pix.y[n] - pix.y[0];
var cut = croppedCtx.getImageData(pix.x[0], pix.y[0], w, h);
croppedCanvas.width = w;
croppedCanvas.height = h;
croppedCtx.putImageData(cut, 0, 0);
return croppedCanvas.toDataURL("image/png");
}
imageData 详解
2018.08.08
