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### 4.22.1 Clicking on Objects

This section describes how you can find out on which object a mouse has clicked.

#### The Code

Best way to explain this is by showing code:

    iMeshWrapper* ClickedObject (iCamera* camera, int mousex, int mousey)
    {
      // Setup a 2D vector with our mouse position.  We invert the y
      // (based on vertical screen dimension) because CS assumes y=0
      // is down for 3D calculations.
      csVector2 v2d (mousex, camera->GetShiftY () * 2 - mousey);

      // We calculate the inverse perspective of this 2D point at
      // z=100.  This results in a 3D position in camera space at
      // z=100 that directly corresponds to the 2D position we
      // clicked on.  We use z=100 to ensure that we will at least
      // hit all objects that are before that distance.
      csVector3 v3d;
      camera->InvPerspective (v2d, 100, v3d);

      // We are going to cast a beam in the current sector of the
      // camera from our camera position in the direction of the
      // 'v3d' point.  First we transform the v3d camera space
      // location to world space.
      csVector3 startbeam = camera->GetTransform ().GetOrigin ();
      csVector3 endbeam = camera->GetTransform ().This2Other (v3d);
      csVector3 intersect;

      // Now do the actual intersection.
      int poly = -1;
      iSector* beamsector = camera->GetSector ();
      iMeshWrapper* mesh =
        beamsector->HitBeamPortals(startbeam, endbeam, intersect, &poly);
      return mesh;
    }

#### Include Files

The include files useful for this section are:

    #include <csgeom/transfrm.h>
    #include <iengine/camera.h>
    #include <iengine/sector.h>
    #include <iengine/mesh.h>

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