[20] 鼓状物(Drum)图形的生成算法

顶点数据的生成

 bool   YfBuildDrumVertices
 (
     Yreal                   radius,
     Yreal                   assistRadius,
     Yuint                   slices,
     Yuint                   stacks,
     YeOriginPose            originPose,
     Yuint                   vertexStriding,
     Yuint                   vertexPos,
     void*                   pVerticesBuffer
 )
 {
     if (slices <  || stacks <  || !pVerticesBuffer)
     {
         return false;
     }

     Yuint numVertices  = slices * stacks + ;

     // 顶点赋值
     char* vertexPtr   = (char*)pVerticesBuffer + vertexPos;
     YsVector3* curVertexPtr   = NULL;
     Yuint nOffset = ;

     Yreal originOffsetY = 0.0f;
     if (originPose == YE_ORIGIN_POSE_TOP)
     {
         originOffsetY = -radius;
     }
     else if (originPose == YE_ORIGIN_POSE_BOTTOM)
     {
         originOffsetY = radius;
     }

     Yreal* pSinList = YD_NEW_ARRAY(Yreal, slices);
     Yreal* pCosList = YD_NEW_ARRAY(Yreal, slices);
     Yreal angleXZ;
     for (Yuint j = ; j < slices; j++)
     {
         angleXZ = YD_REAL_TWAIN_PI * j / slices;
         pSinList[j] = yf_sin(angleXZ);
         pCosList[j] = yf_cos(angleXZ);
     }

     // 赋值
     {
         // 第一个顶点
         {
             nOffset = ;
             curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
             curVertexPtr->x = 0.0f;
             curVertexPtr->y = radius + originOffsetY;
             curVertexPtr->z = 0.0f;
         }

         // 最后一个顶点
         {
             nOffset = (numVertices - ) * vertexStriding;
             curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
             curVertexPtr->x = 0.0f;
             curVertexPtr->y = -radius + originOffsetY;
             curVertexPtr->z = 0.0f;
         }

         for (Yuint i = ; i < stacks; i++)
         {
             Yreal angleY = YD_REAL_PI * i / (stacks - );
             Yreal posY = radius * yf_cos(angleY);
             Yreal radiusXZ = assistRadius + radius * yf_sin(angleY);
             Yreal posX, posZ;

             for (Yuint j = ; j < slices; j++)
             {
                 posX = radiusXZ * pSinList[j];
                 posZ = radiusXZ * pCosList[j];
                 nOffset = (i * slices + j + ) * vertexStriding;
                 curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
                 curVertexPtr->x = posX;
                 curVertexPtr->y = posY + originOffsetY;
                 curVertexPtr->z = posZ;
             }
         }
     }

     YD_SAFE_DELETE_ARRAY(pSinList);
     YD_SAFE_DELETE_ARRAY(pCosList);

     return true;
 }

三角形索引数据的生成和线框索引数据的生成算法与球的类似

 bool   YfBuildDrumTriIndices
 (
     Yuint                   slices,
     Yuint                   stacks,
     YeIndexType             indexType,
     Yuint                   indexStriding,
     Yuint                   indexPos,
     void*                   pTriIndicesBuffer
 )
 {
     return YfBuildSphereTriIndices(
         slices,
         stacks + ,
         indexType,
         indexStriding,
         indexPos,
         pTriIndicesBuffer);
 }

 bool   YfBuildDrumWireIndices
 (
     Yuint                   slices,
     Yuint                   stacks,
     YeIndexType             indexType,
     Yuint                   indexStriding,
     Yuint                   indexPos,
     void*                   pWireIndicesBuffer
 )
 {
     return YfBuildSphereWireIndices(
         slices,
         stacks + ,
         indexType,
         indexStriding,
         indexPos,
         pWireIndicesBuffer);
 }