Best Ray Casting for y = 0

Troubleshooting graphics
1

Hello everyone,

I have a fairly simple problem:

I have a 2 dimensional map, with varying models loaded on top. However, the models aren’t everywhere. If a tile is missing, nothing is drawn.
When the user clicks, I want to know the hypothetical position of the object, and draw a model there. Thus, I need to know from a screen click (or tap), what position on y=0 the user meant.
I thought of two different solutions, but could not quite solve the problem:

  1. Use a Ray and an invisible Spatial. Maybe I could cull the spatial backwards, but that seems excessive and not optimal.
  2. Use some vector magic using cam.getDirection() and cam.getLocation. I tried this, but it failed (not sure why). I used: origin + (origin.y / -direction.y) * direction.

What is the best/most efficient way of doing this?

PS: I don’t think you need any code, but feel free to ask if you need it.

2

Off the top of my head… something like:

Vector3f camLoc = ...
Vector3f camDir = ...

float distance = FastMath.abs(camLoc.y / camDir.y);
Vector3f groundIntersect = camLoc.add(camDir.mult(distance));

Edit: fixed distance calc… though note it now means you will get strange values if you look up.

3

It works, thanks!

That’s no problem, I’ll just add in an if for when dir.y isn’t within -0.5 and +0.5.

4

My example will give you a proper value as long as dir.y < 0. Else it will give you a point in the sky over the ground point that is a mirror of that point from your current location.

5

Ah yes, I was a bit confused.

Looking at the horizon will of course give you a value of y=0.
Thanks again.