Detect collision by drawing line

[Lyian]

Hi Community!

 

I try to draw a line which follows the angle of my cursor. It shouldn't stop at my cursor but rather follow its direction until a collision happens. 

As for now I am able to draw the line on every update which follows perfectly my cursor, but stops then. 
I had the idea to "fire" a sensor (trigger) along the line to check when a collision happens. 

My goal is to archieve this effect with p2js.

 

 

create(){game.input.addMoveCallback(move, this);}    function draw(){       bmd.clear();    bmd.ctx.beginPath();    bmd.ctx.beginPath();    bmd.ctx.moveTo(ship.x, ship.y);    bmd.ctx.lineTo(game.input.x , game.input.y);    bmd.ctx.lineWidth = 4;    bmd.ctx.stroke();    bmd.ctx.closePath();    bmd.render();   }function move(pointer, x, y, isDown) {    mouseBody.body.x= x;    mouseBody.body.y= y;  }function update() {        draw();    }

[drhayes]

I'm not super familiar with P2, haven't used it yet. But you could spawn a body and set its x and y velocity according to the angle and length of the line, right? Then collide with that as it moved? Or do you already have that working?

[Lyian]

Actually I have a line which is drawn between cursor and a ball which is fired by clicking. So the length is in this case determined by the cursor on the screen but should be determined by collision, like in the picture above. 
My idea was to use sensors and fire them along the line until a collision happens, but firstly I dont't know how to do this exactly and I am afraid that the collision won't work at the speed which is required to let the line appear instantly. 

 

[drhayes]

Y'know, since you're making a pool game you probably don't need to rely on the physics simulation to draw this line for you. You're guaranteed to have an upper limit on the number of bodies you care about (20 at most) and calculating an intersection of a line and a circle is pretty cheap. So maybe just iterate through every ball in your world and check to see if/where it intersects the line then draw the result in real time. That way you don't have to worry about tunneling, etc.

 

This article looks promising: http://math.stackexchange.com/questions/228841/how-do-i-calculate-the-intersections-of-a-straight-line-and-a-circle

[Lyian]

Thank you for your help! I'll try it and post the results as soon as I am done!