Detailed explanation of the use of canvas's drawing api

This time I will bring you a detailed explanation of the use of canvas's drawing api. What are the things to note when using canvas's drawing api? The following is a practical case, let's take a look.Canvas can draw many wonderful styles and beautiful effects. Through a few simple APIs, you can present ever-changing effects on the canvas. You can also create web games. Next, I will summarize what is related to drawing. API.

When painting, canvas is equivalent to the canvas, and context is equivalent to the brush.

1. Draw linesmoveTo(x0,y0): Move the current brush (ictx) to the position (x0,y0) .

lineTo(x1,y1): Draw a straight line from the current position (x0, y0) to (x1, y1).

beginPath(): Open a path or reset the current path.

closePath(): Return to the starting point of the path from the current point, which is the position, avoidance and path of the previous beginPath.

stroke(): draw. This

must be added before the picture can be drawn, so this must be placed at the end.

var icanvas=document.getElementById("iCanvas"); var ictx=icanvas.getContext("2d"); ictx.beginPath(); ictx.moveTo(0,0); ictx.lineTo(300,150); ictx.lineTo(3,150); ictx.closePath(); ictx.stroke();

It should be noted here that if closepath is placed after the stroke function, it will not be drawn into a closed line, because before closing , has been drawn, so the straight line on the left will not be drawn.

2. Line stylelineCap: Line endpoint style, butt, round, square. through miterLimet can also be used to set the maximum length of the inflection point junction.　　　　　

miterLimet: If the miter length exceeds the value of miterLimit, the corners will be displayed with the "bevel" type of lineJoin.

lineWidth: line width

strokeStyle: line color, gradient (defined gradientobject

var iCanvas=document.getElementById("iCanvas"); var ictx=iCanvas.getContext("2d"); ictx.beginPath(); ictx.strokeStyle="#0000ff"; ictx.lineWidth=20; ictx.lineCap="round"; ictx.moveTo(10,10); ictx.lineTo(80,80); ictx.stroke(); ictx.beginPath();//在这里必须beginPath，不然一直会以第一个为基础会话，在最后的stroke的时候，会再次画一条黑色的斜线，一共3条线。 ictx.strokeStyle="#000000"; ictx.lineCap="butt"; ictx.lineWidth=10; ictx.moveTo(80,10); ictx.lineTo(10,80); ictx.stroke();

3. Draw a curve

arcTo(x1,y1,x2,y2,radius): draw two The curve before the tangent.

ictx.beginPath(); ictx.moveTo(20,20); // 创建开始点 ictx.lineTo(100,20); // 创建水平线 ictx.arcTo(150,20,150,70,50); // 创建弧 ictx.lineTo(150,120); // 创建垂直线 ictx.stroke();

quadraticCurveTo(x1,y1,x2,y2): quadratic Bezier curve. (x1, y1) The coordinates of the control point, (x2, y2) the coordinates of the end point

bezierCurveTo(x1,y1,x2,y2,x,y): cubic Bezier curve. (x1, y1) The coordinates of control point 1, (x2, y2) The coordinates of control point 2 (x, y) The coordinates of the end point.

Bezier curves are very useful when drawing some very smooth curves.

fillRect(x,y,width ,height): Draw a filled rectangle: (x, y) starting point, width, height rectangle width and height

ictx.fillStyle="#0000ff";//设定填充颜色 ictx.fillRect(20,20,150,100); ictx.strokeRect(180,20,100,100);

fillStyle:设置填充的颜色，渐变或模式（patten）；

strokeStyle：画笔的颜色，渐变或者模式

6.绘制阴影

shadowColor：阴影yanse

shadowBlur:模糊级别

shadowOffsetX：阴影的水平距离

shadowOffsetY：阴影的垂直距离

ictx.shadowBlur=20; ictx.shadowColor="#456"; ictx.shadowOffsetX=-10; ictx.shadowOffsetY=30;//先设置阴影再画矩形 ictx.fillStyle="#108997"; ictx.fillRect(20,20,100,80); ictx.stroke();

7.绘制渐变

createLinearGradient(x1,y1,x2,y2):绘制线性渐变，(x1,y1)是渐变的起始点，（x2,y2）是渐变的终点，位置不同可以制作出垂直或者水平渐变。

createRadialGradient(x1,y1,r1,x2,y2,r2)：径向渐变：，(x1,y1)是渐变的起始点圆心，r1是半径，（x2,y2）是渐变的终点，r2是结束点半径;

两种渐变都需要使用

addColorStop(stop,color)来设置渐变过程，stop是0.0到1.0的值。

var grd=ictx.createLinearGradient(0,0,170,0); grd.addColorStop(0,"#000"); grd.addColorStop(0.5,"#378923"); grd.addColorStop(1,"#ddd"); ictx.fillStyle=grd;//这里渐变是一个对象，用来向fillstyle传值 ictx.fillRect(20,20,150,100); var grd=ictx.createRadialGradient(300,225,15,250,225,100); grd.addColorStop(0,"#345"); grd.addColorStop(1,"#fff"); ictx.fillStyle=grd; ictx.fillRect(200,150,150,100);

8.填充背景

createPattern(image,"repeat|repeat-x|repeat-y|no-repeat"):image是一个图片对象，后面的参数是用来设定图片的重复方式。

9.其他相关API

fill():填充当前路径。

isPointInPath():ictx.isPointInPath(x,y);判断这个点是否位于当前路径

清除画布方法：获取画布的宽高，icanvas.height,icanvas.width;然后使用clearRect();

修改画布的宽高：icanvas.width='200'；icanvas.width='300'的方法。

globalAlpha:设置透明度，只能是0~1的数字，如果透明度不一样，在画第二幅之前重新设置即可。

toDataURL:icanvas.toDataURL(type,encoderOptions)，这个函数返回一个image的base64的URI，参数都是可选的，type可以设置图片类型如image/jpeg,image/webp，默认是image/png；encoderOptions是一个0~1的数字，用来设置image/jpeg,image/webp的图片质量，其他格式的type设置这个参数无效。

10.剪裁

clip():从画布中剪裁任意形状和尺寸的画布，之后所有的绘图都会被限制在剪裁的区域内。这个方法通常和绘制矩形，圆形等路径一起使用，在这些方法后面，剪切这个图像，后来画的就必须在这个剪切后的画布上了。

ictx.arc(100,100,50,(Math.PI/180)*0,(Math.PI/180)*360,true); ictx.stroke(); ictx.clip(); ictx.fillStyle="green"; ictx.fillRect(0,0,150,100);

如果还想操作外部的画布，在剪切前使用save()函数保存，剪切后使用restore()函数恢复到之前保存的状态，但是中间做的操作不会消失哈。

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