[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 < 2 || stacks < 3 || !pVerticesBuffer)
    {
        return false;
    }

    Yuint numVertices  = slices * stacks + 2;

    // 顶点赋值
    char* vertexPtr   = (char*)pVerticesBuffer + vertexPos;
    YsVector3* curVertexPtr   = NULL;
    Yuint nOffset = 0;

    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 = 0; 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 = 0;            
            curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
            curVertexPtr->x = 0.0f;
            curVertexPtr->y = radius + originOffsetY;
            curVertexPtr->z = 0.0f;
        }

        // 最后一个顶点
        {        
            nOffset = (numVertices - 1) * vertexStriding; 
            curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
            curVertexPtr->x = 0.0f;
            curVertexPtr->y = -radius + originOffsetY;
            curVertexPtr->z = 0.0f;
        }

        for (Yuint i = 0; i < stacks; i++)
        {
            Yreal angleY = YD_REAL_PI * i / (stacks - 1);
            Yreal posY = radius * yf_cos(angleY);
            Yreal radiusXZ = assistRadius + radius * yf_sin(angleY);
            Yreal posX, posZ;

            for (Yuint j = 0; j < slices; j++)
            {
                posX = radiusXZ * pSinList[j];
                posZ = radiusXZ * pCosList[j];
                nOffset = (i * slices + j + 1) * 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 + 2, 
        indexType,
        indexStriding,  
        indexPos,
        pTriIndicesBuffer);
}

bool   YfBuildDrumWireIndices
(
    Yuint                   slices,
    Yuint                   stacks, 
    YeIndexType             indexType,
    Yuint                   indexStriding,  
    Yuint                   indexPos,
    void*                   pWireIndicesBuffer
)
{
    return YfBuildSphereWireIndices(
        slices,
        stacks + 2, 
        indexType,
        indexStriding,  
        indexPos,
        pWireIndicesBuffer);
}