Transparent Shadow Plane

Troubleshooting graphics
1

I’ve been playing around with texturing and shadow and I am now wondering what would be the (best) way to create a transparent shadow plane. Given the screenshot of my test game (below), how would I render the shadows of the model over the background, but not the plane itself?







I’m extending StandardGame and have a PassManager for the Background, Shadow and Main pass. Any sample code with a transparent floor plane would help?



Here’s my part of my code if it helps.



Code that creates the floor plane for now:


   public static void initGround() {
      groundNode = new Node("Ground Node");
       Box b = new Box("Ground", new Vector3f(0, 0, 0), 300, 200, 0.1f);
      //Quad b = new Quad("Ground", 300, 200);
      float[] xRotation = {(float)(Math.PI/2.0), 0.0f, 0.0f};
      b.setLocalRotation(new Quaternion(xRotation));
      groundNode.attachChild(b);
      
      MaterialState ms = DisplaySystem.getDisplaySystem().getRenderer().createMaterialState();
      ms.setAmbient(new ColorRGBA(1.0f, 1.0f, 1.0f, 0.5f));
      ms.setDiffuse(new ColorRGBA(0.0f, 0.0f, 1.0f, 0.5f));
      groundNode.setRenderState(ms);
      
      AlphaState as = DisplaySystem.getDisplaySystem().getRenderer().createAlphaState();
      as.setBlendEnabled(true);
      as.setSrcFunction(AlphaState.SB_SRC_ALPHA);
      as.setDstFunction(AlphaState.DB_ONE_MINUS_SRC_ALPHA);
      as.setTestEnabled(true);
      as.setTestFunction(AlphaState.TF_GREATER);
      as.setEnabled(true);
      groundNode.setRenderState(as);
      
      groundNode.updateRenderState();
      gameState.getRootNode().attachChild(groundNode);
   }



And from the extended GameState:


      backNode = new Node("Background Node");

      //XXX START OF STAGE (to replace)
      Quad back = new Quad("Background Quad", this.width, this.height);
      back.setRenderQueueMode(Renderer.QUEUE_ORTHO);
      back.setLocalTranslation(this.width / 2, this.height / 2, 0);
      back.setLightCombineMode(LightState.OFF);

      //XXX should pass background texture folder and load them all
      TextureState ts = DisplaySystem.getDisplaySystem().getRenderer().createTextureState();
      ts.setTexture(TextureManager.loadTexture(
            this.getClass().getClassLoader().getResource("data/habitats/hbhabitat/default.jpg"),
            Texture.MM_LINEAR, Texture.FM_LINEAR, 1.0f, true));
      ts.setEnabled(true);
      back.setRenderState(ts);
      back.updateRenderState();
      //END OF STAGE
   
      backNode.attachChild(back);
                  
      //create the pass manager
      pManager = new BasicPassManager();

      //add the background pass
      backgroundPass = new RenderPass();
      backgroundPass.add(backNode);
      pManager.add(backgroundPass);      

      //add the shadow pass
      shadowPass = new ShadowedRenderPass();
        shadowPass.add(rootNode);
      shadowPass.setShadowColor(ColorRGBA.black);
        shadowPass.setLightingMethod(ShadowedRenderPass.ADDITIVE);
        //shadowPass.setLightingMethod(ShadowedRenderPass.MODULATIVE);
        shadowPass.setRenderShadows(true);
        shadowPass.setEnabled(true);
        shadowPass.addOccluder(rootNode);
        pManager.add(shadowPass);   

      //add the main pass
      rootPass = new RenderPass();
      rootPass.add(rootNode);
      pManager.add(rootPass);



Thanks
2

Let me try to specify a bit. The best way I found at this point to cast shadows on an 'invisible' object, is for the 'invisible' object to have a material with near-zero diffuse alpha, like:



MaterialState ms = DisplaySystem.getDisplaySystem().getRenderer().createMaterialState();
ms.setAmbient(new ColorRGBA(1.0f, 1.0f, 1.0f, 0.0f));
ms.setDiffuse(new ColorRGBA(0.0f, 0.0f, 1.0f, 0.01f));
groundNode.setRenderState(ms);
      
AlphaState as = DisplaySystem.getDisplaySystem().getRenderer().createAlphaState();
as.setBlendEnabled(true);
as.setSrcFunction(AlphaState.SB_SRC_ALPHA);
as.setDstFunction(AlphaState.DB_ONE_MINUS_SRC_ALPHA);
as.setTestEnabled(true);
as.setTestFunction(AlphaState.TF_GREATER);
as.setEnabled(true);
groundNode.setRenderState(as);



The great thing is that the shadows look good, but the 'invisible' object isn't completely transparent outside of the shadows. Setting the alpha value to <0.1f of the material's diffuse only renders it opaque.

Any idea on how I could go about this?