html5 canvas 自動改行でテキストを描画するサンプルコード

<canvas id="canvas" style="border:solid 1px darkgoldenrod;" width="200px" height="100px">& lt;/canvas>

var c=document.getElementById("canvas"); 
var ctx=c.getContext("2d"); 
ctx.fillStyle="#E992B9";
ctx.lineWidth=1;
var str = "If life cheats you, please don't be sad!
ctx.fillText(str,0,20); 

var c=document.getElementById("canvas"); 
var ctx=c.getContext("2d"); 
ctx.fillStyle="#E992B9";
ctx.lineWidth=1; 
var str = "If life cheats you, please don't be sad!
var lineWidth = 0;
var canvasWidth = c.width;//Calculate the width of the canvas
var initHeight=15;//draw the initial height of the font from the top of the canvas
var lastSubStrIndex= 0; //index of the string to start intercepting each time
for(let i=0;i<str.length;i++){ 
    lineWidth+=ctx.measureText(str[i]).width; 
    if(lineWidth>canvasWidth){  
        ctx.fillText(str.substring(lastSubStrIndex,i),0,initHeight);//draw the intercepted part
        initHeight+=20;//20 is the height of the font
        lineWidth=0;
        lastSubStrIndex=i;
    } 
    if(i==str.length-1){//Draw the remaining part
        ctx.fillText(str.substring(lastSubStrIndex,i+1),0,initHeight);
    }
}

/*
str:the string to draw
canvas:canvas object
initX:the starting x coordinate of the string to draw
initY: the y coordinate of the start of the string
lineHeight: the height of the line, define a value yourself
*/
function canvasTextAutoLine(str,canvas,initX,initY,lineHeight){
    var ctx = canvas.getContext("2d"); 
    var lineWidth = 0;
    var canvasWidth = c.width; 
    var lastSubStrIndex= 0; 
    for(let i=0;i<str.length;i++){ 
        lineWidth+=ctx.measureText(str[i]).width; 
        if(lineWidth>canvasWidth-initX){/subtract initX,prevent the problem of border
            ctx.fillText(str.substring(lastSubStrIndex,i),initX,initY);
            initY+=lineHeight;
            lineWidth=0;
            lastSubStrIndex=i;
        } 
        if(i==str.length-1){
            ctx.fillText(str.substring(lastSubStrIndex,i+1),initX,initY);
        }
    }
  }