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HTML5 canvas drawing radioactive gradient color effect code example

小云云

Jan 04, 2018 pm 05:14 PM

canvas html5

This article mainly introduces the effect of drawing radioactive gradient colors on html5 canvas. Friends who need it can refer to it. I hope it can help everyone.

Rendering display:

There are still some pitfalls in canvas. For example, fillRect is a method, not an attribute. If you write fillRect=, it will have no effect. And no error is reported....

The createRadialGradient API is used here. This API receives 6 parameters. The first three represent the bottom circle, and the last three represent the upper circle. The returned instance can still be used with addColorStop.

can2_context is the canvas drawing context of getContext

function Radia(bottom_x,bottom_y,bottom_r,top_x,top_y,top_r){
  this.bottom_x=bottom_x;
  this.bottom_y=bottom_y;
  this.bottom_r=bottom_r;
  this.top_x=top_x;
  this.top_y=top_y;
  this.top_r=top_r;
  this.gradient=can2_context.createRadialGradient(this.bottom_x,this.bottom_y,this.bottom_r,this.top_x,this.top_y,this.top_r)
}
Radia.prototype.addColor=function(){
  for(var i=0;i<arguments.length;i++){
    this.gradient.addColorStop(arguments[i].num,arguments[i].color)
 }
}
Radia.prototype.draw=function(x1,y1,x2,y2){
   can2_context.fillStyle=this.gradient;
   can2_context.fillRect(x1,y1,x2,y2)
}
var some1=new Radia(canvas_2.width/2, canvas_2.height-100, 0, canvas_2.width/2, 0, 300)
some1.addColor({num:0.2,color:"blue"},{num:1,color:"yellow"},{num:0.7,color:"white"})
some1.draw(0, 0, canvas_2.width, canvas_2.height)

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