Draw arrow on canvas tag

Question

I want to draw an arrow using the canvas tag, javascript. I\'ve made it using the quadratic function, but I\'m having problems to calculate the angle of rotation of the arro

Answer 1

Here is the working solution

function draw_arrow(ctx,fx,fy,tx,ty){ //ctx is the context
    var angle=Math.atan2(ty-fy,tx-fx);
    ctx.moveTo(fx,fy); ctx.lineTo(tx,ty);
    var w=3.5; //width of arrow to one side. 7 pixels wide arrow is pretty
    ctx.strokeStyle="#4d4d4d"; ctx.fillStyle="#4d4d4d";
    angle=angle+Math.PI/2; tx=tx+w*Math.cos(angle); ty=ty+w*Math.sin(angle);
    ctx.lineTo(tx,ty);
  //Drawing an isosceles triangle of sides proportional to 2:7:2
    angle=angle-1.849096; tx=tx+w*3.5*Math.cos(angle); ty=ty+w*3.5*Math.sin(angle);
    ctx.lineTo(tx,ty);
    angle=angle-2.584993; tx=tx+w*3.5*Math.cos(angle); ty=ty+w*3.5*Math.sin(angle);
    ctx.lineTo(tx,ty);
    angle=angle-1.849096; tx=tx+w*Math.cos(angle); ty=ty+w*Math.sin(angle);
    ctx.lineTo(tx,ty);
    ctx.stroke(); ctx.fill();
}