Ogre Atomsphere shader - Ogre3d大气层着色器

最近在研究ogre的shader，看了一下官网的教程，鼓捣了一下午总算是把效果搞出来，贴一下关键代码：

                createSphere("sphere",10);

	createSphere("Atomsphere",11);
	Ogre::Entity* PlanetEntity = mSceneMgr->createEntity("planet","sphere");
	PlanetEntity->setMaterialName("Examples/Rockwall");
	Ogre::Entity* AtmosphereEntity = mSceneMgr->createEntity("planet_atm_Ent","Atomsphere");
	//assign it our material
	AtmosphereEntity->setMaterialName ("Atmosphere");
	//also this will make the atmosphere to be rendered behind the planet
	AtmosphereEntity->setRenderQueueGroup (Ogre::RENDER_QUEUE_BACKGROUND);
	//here you will replace PlanetRadius and AtmosphereRadius with your values
	AtmosphereEntity->getSubEntity (0)->setCustomParameter (0, Ogre::Vector4(10,11,0,0));

	Ogre::SceneNode* node1=mSceneMgr->getRootSceneNode()->createChildSceneNode();
	node1->attachObject(PlanetEntity);
	Ogre::SceneNode* node2=mSceneMgr->getRootSceneNode()->createChildSceneNode();
	node2->attachObject(AtmosphereEntity);

    // Set ambient light
    mSceneMgr->setAmbientLight(Ogre::ColourValue(0.5, 0.5, 0.5));

    // Create a light
    Ogre::Light* l = mSceneMgr->createLight("MainLight");
    l->setPosition(20,80,50);

其他的渲染代码、材质脚本代码与官网上的一样，至于那个createsphere是一个自定义函数，参见：

http://wiki.ogre3d.org/ManualSphereMeshes

void createSphere(const std::string& strName, const float r, const int nRings = 16, const int nSegments = 16)
 {
     MeshPtr pSphere = MeshManager::getSingleton().createManual(strName, ResourceGroupManager::DEFAULT_RESOURCE_GROUP_NAME);
     SubMesh *pSphereVertex = pSphere->createSubMesh();
 
     pSphere->sharedVertexData = new VertexData();
     VertexData* vertexData = pSphere->sharedVertexData;
 
     // define the vertex format
     VertexDeclaration* vertexDecl = vertexData->vertexDeclaration;
     size_t currOffset = 0;
     // positions
     vertexDecl->addElement(0, currOffset, VET_FLOAT3, VES_POSITION);
     currOffset += VertexElement::getTypeSize(VET_FLOAT3);
     // normals
     vertexDecl->addElement(0, currOffset, VET_FLOAT3, VES_NORMAL);
     currOffset += VertexElement::getTypeSize(VET_FLOAT3);
     // two dimensional texture coordinates
     vertexDecl->addElement(0, currOffset, VET_FLOAT2, VES_TEXTURE_COORDINATES, 0);
     currOffset += VertexElement::getTypeSize(VET_FLOAT2);
 
     // allocate the vertex buffer
     vertexData->vertexCount = (nRings + 1) * (nSegments+1);
     HardwareVertexBufferSharedPtr vBuf = HardwareBufferManager::getSingleton().createVertexBuffer(vertexDecl->getVertexSize(0), vertexData->vertexCount, HardwareBuffer::HBU_STATIC_WRITE_ONLY, false);
     VertexBufferBinding* binding = vertexData->vertexBufferBinding;
     binding->setBinding(0, vBuf);
     float* pVertex = static_cast<float*>(vBuf->lock(HardwareBuffer::HBL_DISCARD));
 
     // allocate index buffer
     pSphereVertex->indexData->indexCount = 6 * nRings * (nSegments + 1);
     pSphereVertex->indexData->indexBuffer = HardwareBufferManager::getSingleton().createIndexBuffer(HardwareIndexBuffer::IT_16BIT, pSphereVertex->indexData->indexCount, HardwareBuffer::HBU_STATIC_WRITE_ONLY, false);
     HardwareIndexBufferSharedPtr iBuf = pSphereVertex->indexData->indexBuffer;
     unsigned short* pIndices = static_cast<unsigned short*>(iBuf->lock(HardwareBuffer::HBL_DISCARD));
 
     float fDeltaRingAngle = (Math::PI / nRings);
     float fDeltaSegAngle = (2 * Math::PI / nSegments);
     unsigned short wVerticeIndex = 0 ;
 
     // Generate the group of rings for the sphere
     for( int ring = 0; ring <= nRings; ring++ ) {
         float r0 = r * sinf (ring * fDeltaRingAngle);
         float y0 = r * cosf (ring * fDeltaRingAngle);
 
         // Generate the group of segments for the current ring
         for(int seg = 0; seg <= nSegments; seg++) {
             float x0 = r0 * sinf(seg * fDeltaSegAngle);
             float z0 = r0 * cosf(seg * fDeltaSegAngle);
 
             // Add one vertex to the strip which makes up the sphere
             *pVertex++ = x0;
             *pVertex++ = y0;
             *pVertex++ = z0;
 
             Vector3 vNormal = Vector3(x0, y0, z0).normalisedCopy();
             *pVertex++ = vNormal.x;
             *pVertex++ = vNormal.y;
             *pVertex++ = vNormal.z;
 
             *pVertex++ = (float) seg / (float) nSegments;
             *pVertex++ = (float) ring / (float) nRings;
 
             if (ring != nRings) {
                                // each vertex (except the last) has six indices pointing to it
                 *pIndices++ = wVerticeIndex + nSegments + 1;
                 *pIndices++ = wVerticeIndex;               
                 *pIndices++ = wVerticeIndex + nSegments;
                 *pIndices++ = wVerticeIndex + nSegments + 1;
                 *pIndices++ = wVerticeIndex + 1;
                 *pIndices++ = wVerticeIndex;
                 wVerticeIndex ++;
             }
         }; // end for seg
     } // end for ring
 
     // Unlock
     vBuf->unlock();
     iBuf->unlock();
     // Generate face list
     pSphereVertex->useSharedVertices = true;
 
     // the original code was missing this line:
     pSphere->_setBounds( AxisAlignedBox( Vector3(-r, -r, -r), Vector3(r, r, r) ), false );
     pSphere->_setBoundingSphereRadius(r);
         // this line makes clear the mesh is loaded (avoids memory leaks)
         pSphere->load();
  }

参数说明：

r - 半径

nRings - 圈数

nSegments - 段数