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Dragging Atomics
[Tutorial 2 - User Interaction]

Our next goal is to be able to drag the selected atomic about the screen. This will require some modifications to the code we have written in the Idle() function. The code we write will enter a pick-and-translate mode when the left mouse button is pressed. As the mouse moves we will update the position of the selected atomic. When the mouse is released, we will drop the atomic.

• Alter the MouseMoveOperation type to allow a pick-and-translate mode:

      #ifndef UTILS
      #define UTILS
  

      typedef enum {
          MMNoOperation,
          MMPickAndTranslateObject,
  

          MMTranslateObject,
  

          MOUSEMOVEOPERATIONFORCEENUMSIZEINT = RWFORCEENUMSIZEINT
      } MouseMoveOperation;
  

• Change the code in win/events.c to enter the MMPickAndTranslateObject mode when the left mouse button is pressed down. When the mouse button is released enter the MMNoOperation mode.

      static RsEventStatus
      HandleLeftButtonDown(RsMouseStatus *mouseStatus)
      {
          /* Left mouse button down event handling...  */
  

              MouseMoveAction = MMPickAndTranslateObject;
  

          return rsEVENTPROCESSED;
      }
  

      /* HandleLeftButtonUp Function */
      static RsEventStatus
      HandleLeftButtonUp(RsMouseStatus *mouseStatus __RWUNUSED__)
      {
          /* Left mouse button up event handling... */
          MouseMoveAction = MMNoOperation;
          return rsEVENTPROCESSED;
      }
  

  When the atomic is being dragged around the scene, we will use the axes of the camera to decide in which direction the atomic should move. This ensures that the atomic is moved about in a plane that is perpendicular to the camera's look-at vector.

• Add the following code to main.c to perform the translation, and create RwV2d OldPos as a file global variable. We will call the TranslateAtomic() function whenever the mouse is dragged around the scene.

      static void
      TranslateAtomic(void)
      {
          RwReal dx, dy;
          RwFrame *f;
          RwV3d up, right, trans;
  

          f = RwCameraGetFrame(Camera);
          dx = OldPos.x - MousePos.x;
          dy = OldPos.y - MousePos.y;
  

          right = *RwMatrixGetRight(RwFrameGetMatrix(f));
          up = *RwMatrixGetUp(RwFrameGetMatrix(f));
  

          RwV3dScale(&right, &right, dx*0.01f);
          RwV3dScale(&up, &up, dy*0.01f);
          RwV3dAdd(&trans, &up, &right);
  

          f = RpAtomicGetFrame(PickedAtomic);
          RwFrameTranslate(f, &trans, rwCOMBINEPOSTCONCAT);
  

          OldPos = MousePos;
      }
  

      static void 
      Idle(void)
  

• Next we have to change the Idle() function to process the new MouseMoveAction. If we detect a pick-and-translate mode, then we will perform a pick, and then switch to a translate state. In the translate state we will call the TranslateAtomic() function to use the change in mouse position to translate the atomic. Modify the Idle() function as shown:

          /* Update any animations here... */
          lastAnimTime = thisTime;
          switch(MouseMoveAction)
          {
          case MMPickAndTranslateObject :
              PickedAtomic = RwCameraPickAtomicOnPixel(Camera, &MousePos);
              if (PickedAtomic)
              {
                  AtomicGetBBox(PickedAtomic, &PickBox);
                  OldPos = MousePos;
                  MouseMoveAction = MMTranslateObject;
              }
              else
              {
                  MouseMoveAction = MMNoOperation;
              }
              break;
  

          case MMTranslateObject :
              TranslateAtomic();
              break;
  

          default:
              PickedAtomic = NULL;
              break;
          }
          Render();
  

• Run the application and create a few atomics. Select some and drag them about the screen.
  

Next...

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