详解通过变换矩阵实现canvas的缩放功能

 let delta = this.deltaInst;
 delta.bind('zoom', (data) => {
 delta._transform.scale.forEach((s, i) => {
   delta._transform.scale[i] *= data.delta > 0? 2 : 1/2;
 });
 let offsetX = data.x - delta._transform.translate[0];
 let offsetY = data.y - delta._transform.translate[1];
 delta._transform.translate[0] += -(data.delta > 0? 1 : -1/2)*offsetX;
 delta._transform.translate[1] -=  (data.delta > 0? 1 : -1/2)*offsetY;
 delta.refreshAll();
});

   let ctx = this.context;
   let matrix = this.getTransformMatrix();
   ctx.save();
   ctx.transform(...matrix);
   //ctx.translate(...this._transform.translate);
   //ctx.scale(...this._transform.scale);
   if (!Array.isArray(shapes)) {
     shapes = [shapes];
   }
   shapes.forEach( (shape) => {
     shape.render(ctx);
   });
   ctx.restore();