HTML5画布(Canvas)速查表

HTML5 <canvas> 标签用于绘制图像。<canvas> 元素本身仅仅是图形的容器，必须使用脚本来完成实际的绘图任务。HTML5 <canvas> 可用于在画布上绘制文本、线条、矩形、圆形等等。

HTML5画布(Canvas)元素

<canvas id="myCanvas" width="500" height="300">

浏览器不支持画布(canvas)时

<canvas id="myCanvas" width="500" height="300">
  your browser doesn't support canvas!
</canvas>

2d context

var context = canvas.getContext('2d');

Webgl context (3d)

var context = canvas.getContext('webgl');

图形

绘制方形

context.rect(x, y, width, height);
context.fill();
context.stroke();

填充区域

context.fillRect(x, y, width, height);

绘制方形的边框

context.strokeRect(x, y, width, height);

绘制圆形

context.arc(x, y, radius, 0, Math.PI * 2);
context.fill();
context.stroke();

风格

填充

context.fillStyle = 'red';
context.fill();

勾勒

context.strokeStyle = 'red';
context.stroke();

线性渐变

var grd = context.createLinearGradient(x1, y1, x2, y2);
grd.addColorStop(0, 'red');   
grd.addColorStop(1, 'blue');
context.fillStyle = grd;
context.fill();

径向渐变

var grd = context.createRadialGradient(x1, y1, radius1, x2, y2, radius2);
grd.addColorStop(0, 'red');
grd.addColorStop(1, 'blue');
context.fillStyle = grd;
context.fill();

图案

var imageObj = new Image();
imageObj.onload = function() {
  var pattern = context.createPattern(imageObj, 'repeat');
  context.fillStyle = pattern;
  context.fill();
};
imageObj.src = 'path/to/my/image.jpg';

交点

context.lineJoin = 'miter|round|bevel';

线头

context.lineCap = 'butt|round|square';

阴影

context.shadowColor = 'black';
context.shadowBlur = 20;
context.shadowOffsetX = 10;
context.shadowOffsetY = 10;

Alpha (透明)

context.globalAlpha = 0.5; // between 0 and 1

颜色格式

字符串

context.fillStyle = 'red';

16进制

context.fillStyle = '#ff0000';

16进制简写

context.fillStyle = '#f00';

RGB

context.fillStyle = 'rgb(255,0,0)';

RGBA

context.fillStyle = 'rgba(255,0,0,1)';

路径

开始路径

context.beginPath();

画线

context.lineTo(x, y);

弧形

context.arc(x, y, radius, startAngle, endAngle, counterClockwise);

二次曲线

context.quadraticCurveTo(cx, cy, x, y);

二次曲线

context.bezierCurveTo(cx1, cy1, cx2, cy2, x, y);

关闭路径

context.closePath();

图片

画图

var imageObj = new Image();
imageObj.onload = function() {
  context.drawImage(imageObj, x, y);
};
imageObj.src = 'path/to/my/image.jpg';

指定尺寸画图

var imageObj = new Image();
imageObj.onload = function() {
  context.drawImage(imageObj, x, y, width, height);
};
imageObj.src = 'path/to/my/image.jpg';

裁剪图片

var imageObj = new Image();
imageObj.onload = function() {
  context.drawImage(imageObj, sx, sy, sw, sh, dx, dy, dw, dh);
};
imageObj.src = 'path/to/my/image.jpg';

文本

写文字

context.font = '40px Arial';
context.fillStyle = 'red';
context.fillText('Hello World!', x, y);

写镂空文字

context.font = '40pt Arial';
context.strokeStyle = 'red';
context.strokeText('Hello World!', x, y);

粗体

context.font = 'bold 40px Arial';

斜体

context.font = 'italic 40px Arial';

对齐方式

context.textAlign = 'start|end|left|center|right';

文字基线

context.textBaseline = 'top|hanging|middle|alphabetic|ideographic
|bottom';

获取文本宽度

var width = context.measureText('Hello world').width;

动画

移动

context.translate(x, y);

扩大缩小

context.scale(x, y);

旋转

context.rotate(radians);

水平翻转

context.scale(-1, 1);

上下翻转

context.scale(1, -1);

自定义变换

context.transform(a, b, c, d ,e, f);

设置变换

context.setTransform(a, b, c, d ,e, f);

切割

context.transform(1, sy, sx, 1, 0, 0);

重置

context.setTransform(1, 0, 0, 1, 0, 0);

状态存储

存储

context.save();

恢复

context.restore();

裁剪

裁剪

// draw path here
context.clip();

图像数据

获取图像数据

var imageData = context.getImageData(x, y, width, height);
var data = imageData.data;

遍历像素点

var imageData = context.getImageData(x, y, width, height);
var data = imageData.data;
var len = data.length;
var i, red, green, blue, alpha;

for(i = 0; i < len; i += 4) {
  red = data[i];
  green = data[i + 1];
  blue = data[i + 2];
  alpha = data[i + 3];
}

沿坐标遍历像素点

var imageData = context.getImageData(x, y, width, height);
var data = imageData.data;
var x, y, red, green, blue, alpha;

for(y = 0; y < imageHeight; y++) {
  for(x = 0; x < imageWidth; x++) {
    red = data[((imageWidth * y) + x) * 4];
    green = data[((imageWidth * y) + x) * 4 + 1];
    blue = data[((imageWidth * y) + x) * 4 + 2];
    alpha = data[((imageWidth * y) + x) * 4 + 3];
  }
}

设置图像数据

context.putImageData(imageData, x, y);

DATA URLS

获取Data URL

var dataURL = canvas.toDataURL();

使用Data URL生成图像

var imageObj = new Image();
imageObj.onload = function() {
  context.drawImage(imageObj, 0, 0);
};

imageObj.src = dataURL;

合成

合成操作

context.globalCompositeOperation = 'source-atop|source-in|source-out|source-over|destination-atop|destination-in|destination-out|destination-over|lighter|xor|copy';