JS_Canvas_context API

// Ready

var elem = document.getElementById("myCanvas");
var context = elem.getContext('2d');

//2D context API----线条

context.fillStyle = '#00f';  //填充色

context.strokeStyle = '#f00'; //边框色

context.moveTo(x,y)           //移动坐标原点

context.fillRect(x,y,width,height); //绘制带填充的矩形

context.strokeRect(x,y,width,height); //绘制只有边框的矩形

context.clearRect(x,y,width,height); //清除部分canvas

context.lineWidth = 4 ;              //边框线

context.fill();

context.stroke();

注意：原点坐标不变，从当前点到下一个点画线

//2D context API----路径

context.beginPath();

context.moveTo(x,y);

context.lineTo(x,y);

context.bezierCurveTo(cp1x,cp1y,cp2x,cp2y,x,y);

context..arc(x,y,radius,start angle,end angle,anticlockwise[false]);

context.closePath();

//2D context API----图像

var img = new Image();

img.src = "img.gif";

context.drawImage(img,x,y,w,h,

context.drawImage(this, 0, 0); //设置坐标，大小不变

context.drawImage(this, 160, 0, 120, 70); //重设大小

context.drawImage(this, 8, 20, 140, 50, 0, 150, 350, 70); //切割并重设大小

//2D context API----像素级操作

createImageData;

getImageData;

putImageData;

//2D context API----文字

设置属性

font;

font-family;

textAlign;

textBaseline;

绘制文字

fillText（"hello",0,0);

strokeText("hello",0,50);

//2D context API----阴影

  context.shadowOffsetX = 5;
  context.shadowOffsetY = 5;
  context.shadowBlur    = 4; //模糊程度
  context.shadowColor   = 'rgba(255, 0, 0, 0.5)';
  context.fillStyle     = '#00f';
  context.fillRect(20, 20, 150, 100);

//2D context API----颜色渐变

context.createLinearGradient(0, 0, elem.width, 0);