LibGDX problem detecting the mouse click on mesh triangles

Newbie & Debugging Questions
#1

Hello,

I have been trying to add mouse click detection on the triangles of the mesh, but it seems that I am doing something wrong and I cannot figure out how to solve the problem.

So before explaining the problem I will define the environment(the full code is available at http://pastebin.java-gaming.org/a6e9e2e8d351b):

  • Camera position

cam = new OrthographicCamera(10, 9);
cam.position.set(0, 5.35f, 2f);
cam.lookAt(0, 0, 0);
cam.near = 0.5f;
cam.far = 12f;
  • Mesh renders 4 vertices.

mesh = new Mesh(true, NUM_COLUMNS * NUM_LINES, (NUM_COLUMNS * 6 - 6) * (NUM_LINES - 1), VertexAttribute.Position(), VertexAttribute.ColorUnpacked());
mesh.setVertices(new float[] { 
    0, 0, 0, 0, 1, 0, 1,
    1, 0, 0, 0, 1, 0, 1, 
    0, 0, 1, 0, 1, 0, 1, 
    1, 0, 1, 0, 1, 0, 1 });
mesh.setIndices(new short[] { 2, 0, 1, 2, 3, 1 });

So when I run the application I try to check if the click was done inside some of the triangles of the mesh. Now the result depends on the position of the camera. When the camera has almost top view(like in the following picture), corresponding to around 6 on Y axes, the click point is being correctly translated to the coordinates and corresponds to what is actually being seen.

When I move camera on the Y axes to lower position (around 2 or 3), so the image looks like the following one

the click is being detected in the completely wrong positions (the red line shows the place where the click is detected)… Which seems to be right according to the coordinates, but not according to what is being seen…

I would like to understand what an I missing to be able to detect clicks on what actually is being seen? The code I use to detect the click is the following:

@Override
	public boolean touchDown(int screenX, int screenY, int pointer, int button) {
		Ray ray = cam.getPickRay(screenX, screenY);
		Vector3 intersection = new Vector3();
		float[] v = new float[NUM_COLUMNS * NUM_LINES * VERTEX_SIZE];
		short[] i = new short[(NUM_COLUMNS * 6 - 6) * (NUM_LINES - 1)];
		mesh.getIndices(i);
		if (Intersector.intersectRayTriangles(ray, mesh.getVertices(v), i,
				VERTEX_SIZE, intersection)) {
			System.out.println(intersection);
		}
		return false;
	}

Thanks a lot for your help!

#2

I have added question to SO(http://stackoverflow.com/questions/33362529/libgdx-incorrectly-detecting-the-mouse-click-on-mesh-triangles), maybe someone visiting SO (but not this forum) has an idea what am I doing wrong

Besides that I have done some drawings and the coordinates reported both by ray source and target, projected to near and far plane(obtained from camera frustrum) does not seem to hit the mesh (in the second scenario, when I click to the red area, rather than mesh). I will model it in Blender, just to make sure that the drawings I have done are correct… In that case I will need to understand what is not being taken into account and how to solve it.

#3

Just to make sure that if someones runs into the same problem, the solution is described below (very stupid bug in my code :D)

The Vertex Shader, in order to determine the position of the vertices, was performing

a_position * u_projectionViewMatrix

multiplication, which was resulting on what was looking fine on the screen, but actually when you compare with actual coordinates of the mesh it was wrong. Now if you check the examples at https://github.com/libgdx/libgdx/wiki/Shaders, you can see, that

gl_Position

is being calculated by multiplying

u_projectionViewMatrix * a_position

Making the correct calculation made the trick.

I also had to change the camera to perspective, since the mesh was not rendered how I wanted it to.