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  /*!
    \class SoGLUpdateAreaElement Inventor/elements/SoGLUpdateAreaElement.h
    \brief The SoGLUpdateAreaElement class is yet to be documented.
  
    \ingroup elements
  
    FIXME: write doc.
  */
  
  #include <Inventor/elements/SoGLUpdateAreaElement.h>
  #include <Inventor/elements/SoViewportRegionElement.h>
  
  #ifdef HAVE_CONFIG_H
  #include <config.h>
  #endif // HAVE_CONFIG_H
  
  #include <Inventor/system/gl.h>
  
  /*!
    \fn SoGLUpdateAreaElement::origin
  
    FIXME: write doc
  */
  
  /*!
    \fn SoGLUpdateAreaElement::size
  
    FIXME: write doc
  */
  
  SO_ELEMENT_SOURCE(SoGLUpdateAreaElement);
  
  /*!
    \copydetails SoElement::initClass(void)
  */
  
  void
  SoGLUpdateAreaElement::initClass(void)
  {
    SO_ELEMENT_INIT_CLASS(SoGLUpdateAreaElement, inherited);
  }
  
  /*!
    Destructor.
  */
  
  SoGLUpdateAreaElement::~SoGLUpdateAreaElement()
  {
  }
  
  // doc from parent
  void
  SoGLUpdateAreaElement::init(SoState * state)
  {
    inherited::init(state);
    this->origin = getDefaultOrigin();
    this->size = getDefaultSize();
  
    // set these to dummy values. scissor test will be disabled
    this->screensize.setValue(0, 0);
    this->screenorigin.setValue(0, 0);
  
    // scissorstate is used to keep track of current scissor
    // test state.
    this->scissorstate = FALSE;
  
    // disabled by default
    glDisable(GL_SCISSOR_TEST);
  }
  
  // doc from parent
  void
  SoGLUpdateAreaElement::push(SoState * state)
  {
    inherited::push(state);
    SoGLUpdateAreaElement * prev = (SoGLUpdateAreaElement*)
      this->getNextInStack();
    this->scissorstate = prev->scissorstate;
  }
  
  // doc from parent
  void
  SoGLUpdateAreaElement::pop(SoState * state,
                             const SoElement * prevTopElement)
  {
    this->scissorstate = ((SoGLUpdateAreaElement*)prevTopElement)->scissorstate;
    this->updategl();
    inherited::pop(state, prevTopElement);
  }
  
  // doc from parent
  SbBool
  SoGLUpdateAreaElement::matches(const SoElement * element) const
  {
    const SoGLUpdateAreaElement * elem = (SoGLUpdateAreaElement*) element;
    return
      this->origin == elem->origin &&
      this->size == elem->size;
  }
  
  // doc from parent
  SoElement *
  SoGLUpdateAreaElement::copyMatchInfo() const
  {
    SoGLUpdateAreaElement * elem = (SoGLUpdateAreaElement*) this->getTypeId().createInstance();
    elem->origin = this->origin;
    elem->size = this->size;
    return elem;
  }
  
  
  /*!
    Sets the update area. This can, for instance, be used when
    rendering in the front buffer, to only render parts of the scene
    during a window expose event.  \a origin and \a size is in
    normalized window coordinates.
  */
  void
  SoGLUpdateAreaElement::set(SoState * const state,
                             const SbVec2f & origin,
                             const SbVec2f & size)
  {
    SoGLUpdateAreaElement * e = (SoGLUpdateAreaElement *)
      inherited::getElement(state, SoGLUpdateAreaElement::classStackIndex);
    if (e) {
      e->origin = origin;
      e->size = size;
      SbVec2s winsize = SoViewportRegionElement::get(state).getWindowSize();
      e->screenorigin[0] = (short) (origin[0]*float(winsize[0]));
      e->screenorigin[1] = (short) (origin[1]*float(winsize[1]));
      e->screensize[0] = (short) (size[0]*float(winsize[0]));
      e->screensize[1] = (short) (size[1]*float(winsize[1]));
  
      e->updategl();
    }
  }
  
  
  /*!
    Returns the current update area.
  
    \sa set()
  */
  SbBool
  SoGLUpdateAreaElement::get(SoState * const state,
                             SbVec2f & origin,
                             SbVec2f & size)
  {
    const SoGLUpdateAreaElement * e = (const SoGLUpdateAreaElement *)
      inherited::getConstElement(state, SoGLUpdateAreaElement::classStackIndex);
    origin = e->origin;
    size = e->size;
  
    return e->isDefault();
  }
  
  /*!
    Returns the default update area origin, (0,0).
  */
  SbVec2f
  SoGLUpdateAreaElement::getDefaultOrigin(void)
  {
    return SbVec2f(0.0f, 0.0f);
  }
  
  /*!
    Returns the default update area size, (1,1).
  */
  SbVec2f
  SoGLUpdateAreaElement::getDefaultSize(void)
  {
    return SbVec2f(1.0f, 1.0f);
  }
  
  // return TRUE if element contains the default values
  SbBool
  SoGLUpdateAreaElement::isDefault(void) const
  {
    return
      this->origin == getDefaultOrigin() &&
      this->size == getDefaultSize();
  }
  
  //
  // keeps GL in sync
  //
  void
  SoGLUpdateAreaElement::updategl(void)
  {
    if (this->isDefault()) {
      if (this->scissorstate) {
        glDisable(GL_SCISSOR_TEST);
        this->scissorstate = FALSE;
      }
    }
    else {
      if (!this->scissorstate) {
        glEnable(GL_SCISSOR_TEST);
        this->scissorstate = TRUE;
      }
      glScissor((GLint) this->screenorigin[0],
                (GLint) this->screenorigin[1],
                (GLint) this->screensize[0],
                (GLint) this->screensize[1]);
    }
  }
  