Drawing arcs with AS3

September 22, 2009 • Actionscript 3, Flash by Emanuele Feronato • 8 Comments

If you have ever tried to draw arcs with AS3 (or AS2), you probably smashed your computer on the floor after spending hours with curveTo().

That’s not what we need when we want to draw simple arcs, without any Bezier curve.

That’s why I made my own function.

It’s not that interesting since it only uses a bit of trigonometry, and obviously I did not write it for the sake of writing a function, but at the moment with this script

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package {
	import flash.display.Sprite;
	public class arc extends Sprite {
		var my_canvas:Sprite = new Sprite();
		var deg_to_rad=0.0174532925;
		public function arc() {
			addChild(my_canvas);
			my_canvas.graphics.lineStyle(20,0xff0000,1);
			draw_arc(my_canvas,250,200,150,14,180,1);
		}
		public function draw_arc(movieclip,center_x,center_y,radius,angle_from,angle_to,precision) {
			var angle_diff=angle_to-angle_from;
			var steps=Math.round(angle_diff*precision);
			var angle=angle_from;
			var px=center_x+radius*Math.cos(angle*deg_to_rad);
			var py=center_y+radius*Math.sin(angle*deg_to_rad);
			movieclip.graphics.moveTo(px,py);
			for (var i:int=1; i<=steps; i++) {
				angle=angle_from+angle_diff/steps*i;
				movieclip.graphics.lineTo(center_x+radius*Math.cos(angle*deg_to_rad),center_y+radius*Math.sin(angle*deg_to_rad));
			}
		}
	}
}

you get this result:

An arc from degree 14 to degree 180. It’s easy and simple and uses trigonometry (check this old tutorial if you think it’s a brain disease)

But the final application is a power meter like the one used in Pumpkin Story, and here it is, with a bit of the previous script and a bit of Flash artillery.

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package {
	import flash.display.Sprite;
	import flash.events.MouseEvent;
	import flash.events.Event;
	public class arc extends Sprite {
		var my_canvas:Sprite = new Sprite();
		var deg_to_rad=0.0174532925;
		var charging:Boolean=false;
		var power:int=0;
		public function arc() {
			addChild(my_canvas);
			stage.addEventListener(MouseEvent.MOUSE_UP, shoot);
			stage.addEventListener(MouseEvent.MOUSE_DOWN,charge);
			addEventListener(Event.ENTER_FRAME, on_enter_frame);
		}
		public function draw_arc(movieclip,center_x,center_y,radius,angle_from,angle_to,precision) {
			var angle_diff=angle_to-angle_from;
			var steps=Math.round(angle_diff*precision);
			var angle=angle_from;
			var px=center_x+radius*Math.cos(angle*deg_to_rad);
			var py=center_y+radius*Math.sin(angle*deg_to_rad);
			movieclip.graphics.moveTo(px,py);
			for (var i:int=1; i<=steps; i++) {
				angle=angle_from+angle_diff/steps*i;
				movieclip.graphics.lineTo(center_x+radius*Math.cos(angle*deg_to_rad),center_y+radius*Math.sin(angle*deg_to_rad));
			}
		}
		public function charge(e:MouseEvent) {
			charging=true;
		}
		public function shoot(e:MouseEvent) {
			charging=false;
			my_canvas.graphics.clear();
			power=0;
		}
		public function on_enter_frame(e:Event) {
			if (charging) {
				power++;
				if (power>=120) {
					power-=120;
				}
				my_canvas.graphics.clear();
				my_canvas.graphics.lineStyle(20,0x000000,1);
				draw_arc(my_canvas,250,200,150,270,270+power*3,1);
			}
		}
	}
}

And this is the result:

Press and hold the mouse to charge the power, release to reset.

Next time, a real-world application of this principle

Download the source code.

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This post has 8 comments

  1. HiddenSpartan

    on September 23, 2009 at 12:52 am

    Type declarations please.

  2. dVyper

    on September 23, 2009 at 6:05 pm

    Yes, the fact that you’ve provided the code and example simply isn’t good enough for us dammit!

  3. Arthur

    on September 23, 2009 at 7:38 pm

    Yes, type declarations! I can see that the functions doesn’t return anything, but don’t know they’re void unless explicitly stated!

  4. maw

    on September 23, 2009 at 10:52 pm

    I also often write libraries for myself (for satisfaction), but I already know this method from “draw advanced methods” for Flash MX at Adobe. Before a year I found this: http://theflashblog.com/?p=429 – more powerful than their own package, than single functions.

  5. Pumpkin Story prototype : Emanuele Feronato

    on September 25, 2009 at 12:22 am

    [...] quick Pumpkin Story prototype is made merging and mixing these scripts: Drawing arcs with AS3 and Creation of a Flash artillery game using [...]

  6. Weekly Shared Items – 29. September, 2009 | TOXIN LABS - weblog of a german design student from wuerzburg

    on September 29, 2009 at 6:11 am

    [...] Drawing arcs with AS3 [...]

  7. John

    on December 18, 2009 at 3:24 am

    This is a really sweet one..
    I’m rewriting it to use a timer for a slideshow I’m making.

  8. invasion

    on May 22, 2010 at 6:12 am

    I was just wondering how to do this.. This is a good starting point for a circular progress bar or in my case gun reload timer. Thanks for posting.

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