[21] Mesh法线的生成算法

// 生成顶点法线
bool                        YfCalculateVertexNormal
(
    void*                   pNormalsBuffer, 
    Yuint                   normalStriding, 
    Yuint                   normalPos,  
    const void*             pVerticesBuffer,
    Yuint                   vertexNum,
    Yuint                   vertexStriding,
    Yuint                   vertexPos,    
    void*                   pIndicesBuffer,
    Yuint                   trianglesNum,
    YeIndexType             indexType,
    Yuint                   indexStriding,
    Yuint                   indexPos 
)
{
    if (!pNormalsBuffer || !pVerticesBuffer || !pIndicesBuffer ||
        vertexNum < 3 || trianglesNum < 1)
    {
        return false;
    }

    char* vertexPtr = (char*)pVerticesBuffer + vertexPos;
    char* normalPtr = (char*)pNormalsBuffer + normalPos;
    char* indexPtr  = (char*)pIndicesBuffer + indexPos;

    const YsVector* curVertexPtr[3];
    YsVector* curNormalPtr[3];
    Yuint nOffset = 0;
    YsVector vSub_1;
    YsVector vSub_2;
    YsVector vCross;

    for (Yuint i = 0; i < vertexNum; i++)
    {
        curNormalPtr[0] = (YsVector*)(normalPtr + i * normalStriding);
        curNormalPtr[0]->SetZero();
    }
  
    if (indexType == YE_INDEX_16_BIT)
    {
        YsTriIndex16* triIndexPtr = NULL;
        for (Yuint i = 0; i < trianglesNum; i++)
        {
            triIndexPtr = (YsTriIndex16*)(indexPtr + i * indexStriding);
            curVertexPtr[0] = (YsVector*)(vertexPtr + triIndexPtr->index0 * vertexStriding);
            curVertexPtr[1] = (YsVector*)(vertexPtr + triIndexPtr->index1 * vertexStriding);
            curVertexPtr[2] = (YsVector*)(vertexPtr + triIndexPtr->index2 * vertexStriding);
            curNormalPtr[0] = (YsVector*)(normalPtr + triIndexPtr->index0 * normalStriding);
            curNormalPtr[1] = (YsVector*)(normalPtr + triIndexPtr->index1 * normalStriding);
            curNormalPtr[2] = (YsVector*)(normalPtr + triIndexPtr->index2 * normalStriding);

            vSub_1 = *curVertexPtr[1] - *curVertexPtr[0];
            vSub_2 = *curVertexPtr[2] - *curVertexPtr[0];
            YfVector3Cross(vCross, vSub_1, vSub_2);
            
            for (Yuint j = 0; j < 3; j++)
            {
                curNormalPtr[j]->x += vCross.x;
                curNormalPtr[j]->y += vCross.y;
                curNormalPtr[j]->z += vCross.z;
            }
        }
    }
    else
    {
        YsTriIndex32* triIndexPtr = NULL;
        for (Yuint i = 0; i < trianglesNum; i++)
        {
            triIndexPtr = (YsTriIndex32*)(indexPtr + i * indexStriding);
            curVertexPtr[0] = (YsVector*)(vertexPtr + triIndexPtr->index0 * vertexStriding);
            curVertexPtr[1] = (YsVector*)(vertexPtr + triIndexPtr->index1 * vertexStriding);
            curVertexPtr[2] = (YsVector*)(vertexPtr + triIndexPtr->index2 * vertexStriding);
            curNormalPtr[0] = (YsVector*)(normalPtr + triIndexPtr->index0 * normalStriding);
            curNormalPtr[1] = (YsVector*)(normalPtr + triIndexPtr->index1 * normalStriding);
            curNormalPtr[2] = (YsVector*)(normalPtr + triIndexPtr->index2 * normalStriding);

            vSub_1 = *curVertexPtr[1] - *curVertexPtr[0];
            vSub_2 = *curVertexPtr[2] - *curVertexPtr[0];
            YfVector3Cross(vCross, vSub_1, vSub_2);

            for (Yuint j = 0; j < 3; j++)
            {
                curNormalPtr[j]->x += vCross.x;
                curNormalPtr[j]->y += vCross.y;
                curNormalPtr[j]->z += vCross.z;
            }
        }
    }

    for (Yuint i = 0; i < vertexNum; i++)
    {
        curNormalPtr[0] = (YsVector*)(normalPtr + i * normalStriding);
        curNormalPtr[0]->Normalize();
    }

    return true;
}