Edge Enhancement and Wireframe Rendering Tutorial

This tutorial demonstrates how to improve the perception of the objects in a scene and how to perform hidden line removal wireframe rendering using the edge extraction and enhnacement capabilities of Visualization Library.

Edge Rendering Off	Silhouettes	Silhouettes + Creases	Silhouettes + Creases + Hidden Lines
Cartoonish models with silhouette enhancement
Hidden line removal wireframe

In this tutorial we will implement a simple application capable of loading models by drag&drop and applying edge enhancement and hidden line removal wireframe rendering to the whole scene. The user will also be able to interactively switch on and off various edge rendering features:

Key	Mode
'1'	edge rendering off
'2'	edge rendering on: silhouette only
'3'	edge rendering on: silhouette + creases
'4'	edge rendering on: silhouette + creases + hidden lines
'5'	hidden line removal wireframe: silhouette + creases
'6'	hidden line removal wireframe: silhouette + creases + hidden lines

The edges are always extracted from the triangles or quads that are part of a vl::Geometry and can be of three types: silhouette edges, crease edges and boundary edges.

• Silhouette edges are those edges that are shared by a backfacing and front facing quad or triangle.

• Crease edges are those edges that are shared by two triangles or quads and that form an angle >= creaseAngle(), ie: 0 means that the two triangles or quads are coplanar; the edges of a cube define 90 degrees angles; the lateral edges of a 10 faces cylinder define 36 (360/10) degrees angles and so on.

• Boundary edges are those edges that belong to a single triangle or quad.

For more information see also vl::EdgeExtractor and vl::EdgeRenderer.

[From App_EdgeRendering.cpp]

class App_EdgeRendering: public BaseDemo
{
public:
  virtual String appletInfo()
  {
    return BaseDemo::appletInfo() + 
    "- '1' = edge rendering off.\n" +
    "- '2' = edge rendering on: silhouette only.\n" +
    "- '3' = edge rendering on: silhouette + creases.\n" +
    "- '4' = edge rendering on: silhouette + creases + hidden lines.\n" +
    "- '5' = edges only: silhouette + creases.\n" + 
    "- '6' = edges only: silhouette + creases + hidden lines.\n" +
    "\n";
  }

  void initEvent()
  {
    vl::Log::notify(appletInfo());

    // retrieve the default rendering
    mMainRendering = rendering()->as<Rendering>();
    // retrieve the default renderer, which we'll use as the solid-renderer
    mSolidRenderer = mMainRendering->renderer();

    // create our EdgeRenderer
    mEdgeRenderer = new EdgeRenderer;
    // we set the clear flags to be CF_CLEAR_DEPTH (by default is set to CF_CLEAR_COLOR_DEPTH) because 
    // when the wireframe rendering starts we want to preserve the color-buffer as generated by the solid 
    // rendering but we want to clear the Z-buffer as it is needed by the hidden-line-removal algorithm 
    // implemented by EdgeRenderer.
    mEdgeRenderer->setClearFlags(CF_CLEAR_DEPTH);
    // target the same opengl window
    mEdgeRenderer->setFramebuffer(mSolidRenderer->framebuffer());
    // enqueue the EdgeRenderer in the rendering, will be executed after mSolidRenderer
    mMainRendering->renderers().push_back( mEdgeRenderer.get() );

    // hidden line and crease options
    mEdgeRenderer->setShowHiddenLines(true);
    mEdgeRenderer->setShowCreases(true);
    mEdgeRenderer->setCreaseAngle(35.0f);

    // style options
    mEdgeRenderer->setLineWidth(2.0f);
    mEdgeRenderer->setSmoothLines(true);
    mEdgeRenderer->setDefaultLineColor(black);

    // fills the scene with a few actors.
    // the beauty of this system is that you setup your actors ony once in a single scene managers and
    // they will be rendered twice, first using a normal renderer and then using the edge renderer.
    setupScene();
  }

  // populates the scene
  void setupScene()
  {
    // setup common states
    ref<Light> camera_light = new Light;
    ref<EnableSet> enables = new EnableSet;
    enables->enable(EN_DEPTH_TEST);
    enables->enable(EN_LIGHTING);

    // red material fx
    ref<Effect> red_fx = new Effect;
    red_fx->shader()->setEnableSet(enables.get());
    red_fx->shader()->gocMaterial()->setDiffuse(red);
    red_fx->shader()->setRenderState(camera_light.get(), 0);

    // green material fx
    ref<Effect> green_fx = new Effect;
    green_fx->shader()->setEnableSet(enables.get());
    green_fx->shader()->gocMaterial()->setDiffuse(green);
    green_fx->shader()->setRenderState(camera_light.get(), 0);

    // blue material fx
    ref<Effect> yellow_fx = new Effect;
    yellow_fx->shader()->setEnableSet(enables.get());
    yellow_fx->shader()->gocMaterial()->setDiffuse(yellow);
    yellow_fx->shader()->setRenderState(camera_light.get(), 0);

    // add box, cylinder, cone actors to the scene
    ref<Geometry> geom1 = makeBox     (vec3(-7,0,0),5,5,5);
    ref<Geometry> geom2 = makeCylinder(vec3(0,0,0), 5,5, 10,2, true, true);
    ref<Geometry> geom3 = makeCone    (vec3(+7,0,0),5,5, 20, true);

    // needed since we enabled the lighting
    geom1->computeNormals();
    geom2->computeNormals();
    geom3->computeNormals();

    // add the actors to the scene
    sceneManager()->tree()->addActor( geom1.get(), red_fx.get(),    mMainRendering->transform() );
    sceneManager()->tree()->addActor( geom2.get(), green_fx.get(),  mMainRendering->transform() );
    sceneManager()->tree()->addActor( geom3.get(), yellow_fx.get(), mMainRendering->transform() );
  }

  // user controls:
  // '1' = edge rendering off.
  // '2' = edge rendering on: silhouette only.
  // '3' = edge rendering on: silhouette + creases.
  // '4' = edge rendering on: silhouette + creases + hidden lines.
  // '5' = edges only: silhouette + creases.
  // '6' = edges only: silhouette + creases + hidden lines.
  void keyPressEvent(unsigned short ch, EKey key)
  {
    BaseDemo::keyPressEvent(ch, key);

    if (ch == '1')
    {
      mSolidRenderer->setEnableMask(0xFFFFFFFF);
      mEdgeRenderer->setEnableMask(0);
      Log::print("Edge rendering disabled.\n");
    }
    else
    if (ch == '2')
    {
      mSolidRenderer->setEnableMask(0xFFFFFFFF);
      // preserve color buffer, clear depth buffer
      mEdgeRenderer->setClearFlags(CF_CLEAR_DEPTH);
      mEdgeRenderer->setEnableMask(0xFFFFFFFF);
      mEdgeRenderer->setShowCreases(false);
      mEdgeRenderer->setShowHiddenLines(false);
      Log::print("Edge rendering enabled. Creases = off, hidden lines = off.\n");
    }
    else
    if (ch == '3')
    {
      mSolidRenderer->setEnableMask(0xFFFFFFFF);
      // preserve color buffer, clear depth buffer
      mEdgeRenderer->setClearFlags(CF_CLEAR_DEPTH);
      mEdgeRenderer->setEnableMask(0xFFFFFFFF);
      mEdgeRenderer->setShowCreases(true);
      mEdgeRenderer->setShowHiddenLines(false);
      Log::print("Edge rendering enabled. Creases = on, hidden lines = off.\n");
    }
    else
    if (ch == '4')
    {
      mSolidRenderer->setEnableMask(0xFFFFFFFF);
      // preserve color buffer, clear depth buffer
      mEdgeRenderer->setClearFlags(CF_CLEAR_DEPTH);
      mEdgeRenderer->setEnableMask(0xFFFFFFFF);
      mEdgeRenderer->setShowCreases(true);
      mEdgeRenderer->setShowHiddenLines(true);
      Log::print("Edge rendering enabled. Creases = on, hidden lines = on.\n");
    }
    else
    if (ch == '5')
    {
      mSolidRenderer->setEnableMask(0);
      // clear color and depth buffer
      mEdgeRenderer->setClearFlags(CF_CLEAR_COLOR_DEPTH);
      mEdgeRenderer->setEnableMask(0xFFFFFFFF);
      mEdgeRenderer->setShowCreases(true);
      mEdgeRenderer->setShowHiddenLines(false);
      Log::print("Hidden line removal wireframe enabled. Creases = on, hidden lines = off.\n");
    }
    if (ch == '6')
    {
      mSolidRenderer->setEnableMask(0);
      // clear color and depth buffer
      mEdgeRenderer->setClearFlags(CF_CLEAR_COLOR_DEPTH);
      mEdgeRenderer->setEnableMask(0xFFFFFFFF);
      mEdgeRenderer->setShowCreases(true);
      mEdgeRenderer->setShowHiddenLines(true);
      Log::print("Hidden line removal wireframe enabled. Creases = on, hidden lines = on.\n");
    }
  }

  void resizeEvent(int w, int h)
  {
    Camera* camera = mMainRendering->camera();
    camera->viewport()->setWidth ( w );
    camera->viewport()->setHeight( h );
    camera->setProjectionPerspective();
  }

  void loadModel(const std::vector<String>& files)
  {
    // resets the scene
    sceneManager()->tree()->actors()->clear();
    // resets the EdgeRenderer cache
    mEdgeRenderer->clearCache();

    for(unsigned int i=0; i<files.size(); ++i)
    {
      ref<ResourceDatabase> resource_db = loadResource(files[i],true);

      if (!resource_db || resource_db->count<Actor>() == 0)
      {
        Log::error("No data found.\n");
        continue;
      }

      std::vector< ref<Actor> > actors;
      resource_db->get<Actor>(actors);
      for(unsigned i=0; i<actors.size(); ++i)
      {
        ref<Actor> actor = actors[i].get();
        // define a reasonable Shader
        actor->effect()->shader()->setRenderState( new Light, 0 );
        actor->effect()->shader()->enable(EN_DEPTH_TEST);
        actor->effect()->shader()->enable(EN_LIGHTING);
        actor->effect()->shader()->gocLightModel()->setTwoSide(true);
        // add the actor to the scene
        sceneManager()->tree()->addActor( actor.get() );
      }
    }

    // position the camera to nicely see the objects in the scene
    trackball()->adjustView( sceneManager(), vec3(0,0,1)/*direction*/, vec3(0,1,0)/*up*/, 1.0f/*bias*/ );
  }

  // laod the files dropped in the window
  void fileDroppedEvent(const std::vector<String>& files) { loadModel(files); }

protected:
  ref< Renderer > mSolidRenderer;
  ref< EdgeRenderer > mEdgeRenderer;
  ref<Rendering> mMainRendering;
};

// Have fun!