Html5使用canvas绘制一些图形(渐变，三角)

Html代码：

 

js代码：

//画布5容量下降的函数
var sY=20;
var sH=50;
var return_val=null;
var cxt5=null;
//第一张画布
var initFirst=function(){
	var obj1=document.getElementById("canvas_f");
	var cxt1=obj1.getContext("2d");
	var grd1=cxt1.createLinearGradient(0,0,100,0);
	grd1.addColorStop(0,"#000000");
	grd1.addColorStop(0.5,"#FFFFFF");
	grd1.addColorStop(1,"#000000");
	cxt1.fillStyle=grd1;
	cxt1.fillRect(0,0,100,100);
}
var initSecond=function(){
	var obj2=document.getElementById("canvas_s");
	var cxt2=obj2.getContext("2d");
	cxt2.strokeStyle="red";
	cxt2.beginPath();
	cxt2.moveTo(50,0);
	cxt2.lineTo(0,100);
	cxt2.lineTo(100,100);
	cxt2.lineTo(50,0);
	cxt2.closePath();
	cxt2.stroke();
}
var initThird=function(){
	//虚拟油罐
	var obj3=document.getElementById("canvas_t");
	cxt3=obj3.getContext("2d");
	//第一个点（坐标）
	cxt3.moveTo(0,20);
	//to第二个点（坐标）
	cxt3.lineTo(50,0);
	cxt3.lineTo(100,20);
	var grd3=cxt3.createLinearGradient(0,20,100,20);
	grd3.addColorStop(0,"#000000");
	grd3.addColorStop(0.5,"#FFFFFF");
	grd3.addColorStop(1,"#000000");
	cxt3.fillStyle=grd3;
	cxt3.fillRect(0,20,90,50);
	cxt3.fillStyle="green";
	cxt3.fillRect(90,20,10,50);
	cxt3.fillStyle="red";
	cxt3.fillRect(90,40,10,30);
	cxt3.stroke();
}
var initFourth=function(){
	var obj4=document.getElementById("canvas_fo");
	var cxt4=obj4.getContext("2d");
	cxt4.moveTo(0,20);
	cxt4.lineTo(50,0);
	cxt4.lineTo(100,20);
	var grd4=cxt4.createLinearGradient(0,20,100,20);
	grd4.addColorStop(0,"#000000");
	grd4.addColorStop(0.5,"#FFFFFF");
	grd4.addColorStop(1,"#000000");
	cxt4.fillStyle=grd4;
	cxt4.fillRect(0,20,100,50);
	cxt4.stroke();
}
function initFive(){
	setCount();
	//通过setInterval控制每秒下降
    return_val=setInterval("setCount()",1000);
}
function setCount(){
	var obj5=document.getElementById("canvas_fi");
	cxt5=obj5.getContext("2d");
	cxt5.fillStyle="#000000";
	cxt5.moveTo(0,20);
	cxt5.lineTo(50,0);
	cxt5.lineTo(100,20);
	cxt5.fill();
	var grd5=cxt5.createLinearGradient(0,20,100,20);
	//渐变
	grd5.addColorStop(0,"#000000");
	grd5.addColorStop(0.5,"#FFFFFF");
	grd5.addColorStop(1,"#000000");
	cxt5.fillStyle=grd5;
    cxt5.fillRect(0,20,100,50);
	//右侧容量条	    
    cxt5.fillStyle=grd5;
	cxt5.fillRect(0,20,90,50);
	cxt5.fillStyle="green";
	cxt5.fillRect(90,20,10,50);
	cxt5.fillStyle="red";
    cxt5.stroke();
    if(sY<70&&sH>0){
		sY=parseInt(sY)+5;
		sH=parseInt(sH)-5;
	}
    console.log("ing..."+sY+"---"+sH);
    cxt5.fillRect(90,sY,10,sH);
    //如果下降到0则停止
    if(sY>=70||sH<=0){
		clearInterval(return_val);
		return_val=null;
	}
}
function initSix(){
	var obj6=document.getElementById("canvas_si");
	var cxt6=obj6.getContext("2d");
	cxt6.moveTo(150,0);
	cxt6.fillStyle="red";
	cxt6.lineTo(100,100);
	cxt6.lineTo(200,100);
	cxt6.lineTo(150,0);
	cxt6.closePath();
	cxt6.fill();
}
function init(){
	//画布1，画渐变
	initFirst();
	//画布2，三角
	//(moveTo:起点（x,y）lineTo从上一个点到下一个点(x,y))
	initSecond();
	//画布3，虚拟油罐
	initThird();
	//画布4
	initFourth();
	//画布5
	initFive();
	//画布6
	initSix();
}

实现效果：