What is the best method in XNA to have the player paint smoothly on the screen?

Question

I'm developing a wp7 game where the player draws lines in the program and a ball bounces off of them. I'm using XNA and farseer physics. What is the best method for a user to draw a line, and then for the program to take it and turn it in to a physics object, or at least a list of vector2s? I've tried creating a list of TouchLocations, but it ends up spotty if the user does not draw very slow, like the picture I've attached. Any suggestions? Thanks http://img829.imageshack.us/img829/3985/capturehbn.png

Here's some code: I'm using the gamestatemanagement sample, and this is in the HandleInput method

foreach (TouchLocation t in input.TouchState) {
  pathManager.Update(gameTime, t.Position);
}

The pathManager class manages a collection of path classes, which are drawable physics objects. Here is pathManager.Update

public void Update(GameTime gameTime, Vector2 touchPosition) {
  paths.Add(new Path(world,texture, new Vector2(5,5) ,0.1f));
  paths[paths.Count-1].Position = touchPosition;
}

This is just what I'm doing now and I'm willing to throw it out for anything. You'd think that having a 5x5 rectangle for each touch location would kill the performance, but using farseer I didn't see any drops, even with a mostly full screen. However, this system doesn't create a smooth line at all if the line is drawn fast.

I doubt this helps any, but here is the Path constructor.

public Path(World world, Texture2D texture, Vector2 size, float mass) {
  this.Size = size;
  this.texture = texture;
  body = BodyFactory.CreateRectangle(world, size.X * pixelToUnit, size.Y * pixelToUnit, 1);
  body.BodyType = BodyType.Static;
  body.Restitution = 1f;
  body.Friction = 0;
  body.Friction = 10;
}

Handfast

Could you paste your relevant code in? – Caernarvonshire

do you have to have more than 2 points of a line? – Souse

I supoose not, but preferably yes. I can see just a straight line though. How would I go about doing that? – Handfast

Im wondering if theres some sort of algorithim to calculate all of the positions inbetween the places it skipped? – Handfast

When you say all positions in between, what do you actually mean? – Stickseed

I mean when it skips over from one point to the next, like in the image link I posted, if there's a way to find all of the points along the slope of the two points it did record? – Handfast

Answer 1

How do I draw lines using XNA?

the best way to draw primitives is to use the basiceffect shader. this will be accelerated by the hardware. you can also add a texture to it if you'd like.

i'm not sure if its the same on WP7 but this works for Windows7 at least.

Pyrogen

Thanks for the answer, I like this method for drawing it, but I'd need to have a list of all the points along the line for collision detection. – Handfast

Well any of the Body's created by the BodyFactory should work. Or do you mean when the lines collide with eachother? In farseer theres a thing called a Contact. Whenever a collision occurs a Contact is created that contains some information about where exactly the collision occured. – Pyrogen

That makes sense. I don't know why I was stuck on a list of vector2s. I ended up using BodyFactory.CreateEdge using the first and last points of a free drag gesture and using your drawing method. Thanks! – Handfast