[7] 金字塔(Pyramid)图形的生成算法

顶点数据的生成

bool                        YfBuildPyramidVertices
(
    Yreal                   width, 
    Yreal                   length, 
    Yreal                   height, 
    YeOriginPose            originPose, 
    Yuint                   vertexStriding, 
    Yuint                   vertexPos,
    void*                   pVerticesBuffer
)
{
    if (!pVerticesBuffer)
    {
        return false;
    }

    Yuint numVertices  = 5;

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

    YsVector3 vOriginOffset(-width / 2, -height / 2, -length / 2);
    if (originPose == YE_ORIGIN_POSE_TOP)
    {
        vOriginOffset.y = -height;
    }
    else if (originPose == YE_ORIGIN_POSE_BOTTOM)
    {
        vOriginOffset.y = 0.0f;
    }

    // 底四个顶点
    for (Yuint j = 0; j < 2; j++)
    {
        for (Yuint i = 0; i < 2; i++)
        {
            nOffset = (j*2 + i) * vertexStriding;
            curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
            curVertexPtr->x = width*i + vOriginOffset.x;
            curVertexPtr->y = vOriginOffset.y;
            curVertexPtr->z = length*j + vOriginOffset.z;
        }
    }

    // 顶尖顶点
    nOffset = 4 * vertexStriding;
    curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
    curVertexPtr->x = 0.0f;
    curVertexPtr->y = height + vOriginOffset.y;
    curVertexPtr->z = 0.0f;
 
    return true;
}     

 

三角形索引数据的生成

 

bool                        YfBuildPyramidTriIndices
(
    YeIndexType             indexType,
    Yuint                   indexStriding,  
    Yuint                   indexPos,
    void*                   pTriIndicesBuffer
)
{
    if (!pTriIndicesBuffer)
    {
        return false;
    }

    char* indexPtr = (char*)pTriIndicesBuffer + indexPos;
    if (indexType == YE_INDEX_16_BIT)
    {
        YsTriIndex16* triIndexPtr = NULL;

        // bottom
        triIndexPtr = (YsTriIndex16*)(indexPtr + 0*indexStriding);
        triIndexPtr->index0 = 0; triIndexPtr->index1 = 1; triIndexPtr->index2 = 3;
        triIndexPtr = (YsTriIndex16*)(indexPtr + 1*indexStriding);
        triIndexPtr->index0 = 0; triIndexPtr->index1 = 3; triIndexPtr->index2 = 2;

        // 4 face
        triIndexPtr = (YsTriIndex16*)(indexPtr + 2*indexStriding);
        triIndexPtr->index0 = 4; triIndexPtr->index1 = 1; triIndexPtr->index2 = 0;
        triIndexPtr = (YsTriIndex16*)(indexPtr + 3*indexStriding);
        triIndexPtr->index0 = 4; triIndexPtr->index1 = 3; triIndexPtr->index2 = 1;
        triIndexPtr = (YsTriIndex16*)(indexPtr + 4*indexStriding);
        triIndexPtr->index0 = 4; triIndexPtr->index1 = 2; triIndexPtr->index2 = 3;
        triIndexPtr = (YsTriIndex16*)(indexPtr + 5*indexStriding);                                                
        triIndexPtr->index0 = 4; triIndexPtr->index1 = 0; triIndexPtr->index2 = 2;
    }
    else
    {
        YsTriIndex32* triIndexPtr = NULL;

        // bottom
        triIndexPtr = (YsTriIndex32*)(indexPtr + 0*indexStriding);
        triIndexPtr->index0 = 0; triIndexPtr->index1 = 1; triIndexPtr->index2 = 3;
        triIndexPtr = (YsTriIndex32*)(indexPtr + 1*indexStriding);
        triIndexPtr->index0 = 0; triIndexPtr->index1 = 3; triIndexPtr->index2 = 2;

        // 4 face
        triIndexPtr = (YsTriIndex32*)(indexPtr + 2*indexStriding);
        triIndexPtr->index0 = 4; triIndexPtr->index1 = 1; triIndexPtr->index2 = 0;
        triIndexPtr = (YsTriIndex32*)(indexPtr + 3*indexStriding);
        triIndexPtr->index0 = 4; triIndexPtr->index1 = 3; triIndexPtr->index2 = 1;
        triIndexPtr = (YsTriIndex32*)(indexPtr + 4*indexStriding);
        triIndexPtr->index0 = 4; triIndexPtr->index1 = 2; triIndexPtr->index2 = 3;
        triIndexPtr = (YsTriIndex32*)(indexPtr + 5*indexStriding);                                                
        triIndexPtr->index0 = 4; triIndexPtr->index1 = 0; triIndexPtr->index2 = 2;
    }

    return true;
}     

 

线框索引数据的生成

bool                        YfBuildPyramidWireIndices
(
    YeIndexType             indexType,
    Yuint                   indexStriding, 
    Yuint                   indexPos,
    void*                   pWireIndicesBuffer
)
{
    if (!pWireIndicesBuffer)
    {
        return false;
    }

    Yuint numVertices = 5;
    Yuint numLines    = 8;
    if (indexType == YE_INDEX_16_BIT && 
        numVertices > YD_MAX_UNSIGNED_INT16)
    {
        return false;
    }

    // 索引赋值
    char* indexPtr = (char*)pWireIndicesBuffer + indexPos;
    Yuint nOffset = 0;
    if (indexType == YE_INDEX_16_BIT)
    {
        YsLineIndex16* lineIndexPtr = NULL;
        
        // bottom
        lineIndexPtr = (YsLineIndex16*)(indexPtr + 0*indexStriding);
        lineIndexPtr->index0 = 0; lineIndexPtr->index1 = 1; 
        lineIndexPtr = (YsLineIndex16*)(indexPtr + 1*indexStriding);
        lineIndexPtr->index0 = 1; lineIndexPtr->index1 = 3; 
        lineIndexPtr = (YsLineIndex16*)(indexPtr + 2*indexStriding);
        lineIndexPtr->index0 = 3; lineIndexPtr->index1 = 2; 
        lineIndexPtr = (YsLineIndex16*)(indexPtr + 3*indexStriding);
        lineIndexPtr->index0 = 2; lineIndexPtr->index1 = 0; 

        // 4 lines
        lineIndexPtr = (YsLineIndex16*)(indexPtr + 4*indexStriding);
        lineIndexPtr->index0 = 4; lineIndexPtr->index1 = 0; 
        lineIndexPtr = (YsLineIndex16*)(indexPtr + 5*indexStriding);
        lineIndexPtr->index0 = 4; lineIndexPtr->index1 = 1; 
        lineIndexPtr = (YsLineIndex16*)(indexPtr + 6*indexStriding);
        lineIndexPtr->index0 = 4; lineIndexPtr->index1 = 2; 
        lineIndexPtr = (YsLineIndex16*)(indexPtr + 7*indexStriding);
        lineIndexPtr->index0 = 4; lineIndexPtr->index1 = 3; 
    }
    else
    {
        YsLineIndex32* lineIndexPtr = NULL;

        // bottom
        lineIndexPtr = (YsLineIndex32*)(indexPtr + 0*indexStriding);
        lineIndexPtr->index0 = 0; lineIndexPtr->index1 = 1; 
        lineIndexPtr = (YsLineIndex32*)(indexPtr + 1*indexStriding);
        lineIndexPtr->index0 = 1; lineIndexPtr->index1 = 3; 
        lineIndexPtr = (YsLineIndex32*)(indexPtr + 2*indexStriding);
        lineIndexPtr->index0 = 3; lineIndexPtr->index1 = 2; 
        lineIndexPtr = (YsLineIndex32*)(indexPtr + 3*indexStriding);
        lineIndexPtr->index0 = 2; lineIndexPtr->index1 = 0; 

        // 4 lines
        lineIndexPtr = (YsLineIndex32*)(indexPtr + 4*indexStriding);
        lineIndexPtr->index0 = 4; lineIndexPtr->index1 = 0; 
        lineIndexPtr = (YsLineIndex32*)(indexPtr + 5*indexStriding);
        lineIndexPtr->index0 = 4; lineIndexPtr->index1 = 1; 
        lineIndexPtr = (YsLineIndex32*)(indexPtr + 6*indexStriding);
        lineIndexPtr->index0 = 4; lineIndexPtr->index1 = 2; 
        lineIndexPtr = (YsLineIndex32*)(indexPtr + 7*indexStriding);
        lineIndexPtr->index0 = 4; lineIndexPtr->index1 = 3; 
    }

    return true;
}