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Highlighting
[Tutorial 2 - User Interaction]

It is convenient for the picked atomic to be highlighted to inform the user which, of possibly many, atomics have been picked. In this simple application we will draw a bounding box around the picked atomic. The coordinates for this bounding box will be computed once when the picking occurs. In a real application these bounding boxes might be computed offline and stored with the atomic using a plugin.

• Add a function called AtomicGetBBox() to utils.c (and extern it in utils.h) to compute the coordinates of a bounding box given an atomic:

      void
      AtomicGetBBox(RpAtomic *atom, RwBBox *box)
      {
          RpGeometry    *geom   = RpAtomicGetGeometry(atom);
          RwInt32        nVerts = RpGeometryGetNumVertices(geom);
          RpMorphTarget *morph  = RpGeometryGetMorphTarget(geom, 0);
          RwV3d         *verts  = RpMorphTargetGetVertices(morph);
          RwUInt16       i;
          box->inf = *verts;
          box->sup = *verts;
          for (verts++, i = 1; i < nVerts; i++, verts++)
          {
              if (verts->x < box->inf.x) box->inf.x = verts->x;
              if (verts->y < box->inf.y) box->inf.y = verts->y;
              if (verts->z < box->inf.z) box->inf.z = verts->z;
              if (verts->x > box->sup.x) box->sup.x = verts->x;
              if (verts->y > box->sup.y) box->sup.y = verts->y;
              if (verts->z > box->sup.z) box->sup.z = verts->z;
          }
  

          RwV3dScale(&box->sup, &box->sup, 1.09f);
          RwV3dScale(&box->inf, &box->inf, 1.09f);
      }
  

• To main.c add a new variable static RwBBox PickBox. If an atomic is returned from the pick test in the Idle() function, call AtomicGetBBox to compute and store the dimensions of the bounding box around the atomic. Compile the code.

  Next we need to add code that will draw the bounding box when there is an atomic selected. To do this we will create a new function in main.c called HighlightRender(). This will be called from the Render() function in main.c to display the bounding box.

• Add the following function to main.c. This code makes use of immediate mode to render a wireframe bounding box around the selected atomic. The lines are drawn in red.

      static void
      HighlightRender(void)
      {
          RwMatrix                  *ltm =
                                      RwFrameGetLTM(RpAtomicGetFrame(PickedAtomic));
          RwIm3DVertex              vertices[8];
          RwInt32                   i;
          static RwImVertexIndex    indices[24] = { 0, 1, 1, 3, 3, 2, 2, 0,
                                                    4, 5, 5, 7, 7, 6, 6, 4,
                                                    0, 4, 1, 5, 2, 6, 3, 7 };
          for (i = 0; i < 8; i++)
  

          {
              RwIm3DVertexSetPos(vertices+i,
                  i&1 ? PickBox.sup.x : PickBox.inf.x,
                  i&2 ? PickBox.sup.y : PickBox.inf.y,
                  i&4 ? PickBox.sup.z : PickBox.inf.z);
              RwIm3DVertexSetRGBA(vertices+i, 255, 0, 0, 255); 
          }
  

          /* all vertices have opaque colors so we can use the rwIM3D_ALLOPAQUE
           * hint for RwIm3DTransform */
          if (RwIm3DTransform(vertices, 8, ltm, rwIM3D_ALLOPAQUE))
          {
              RwIm3DRenderIndexedPrimitive(rwPRIMTYPELINELIST, indices, 24);
              RwIm3DEnd();
          }
  

      }
      /*************************************************************************/
      static void 
      Render(void)
  

• Add a call to the HighlightRender() function in main.c, in the function Render(). This code should only be called if there is a picked atomic:

              if( MenuGetStatus() != HELPMODE )
              {
                  /*
                   * Scene rendering here...
                   */
                  RpWorldRender(World);
                  DisplayOnScreenInfo(Camera);
                  if (PickedAtomic)
                  {
                      HighlightRender();
                  }
              }
              MenuRender(Camera, NULL);
  

• Compile and run the application. Create an atomic (by loading the clump), and select it with the mouse. You should see the bounding box highlighting the atomic. The highlight disappears when you click the background, thereby deselecting the atomic. This demonstrates that the picking code works the way we want it to.
  

Next...

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