[2] 立方体(Box)图形的生成算法

顶点数据的生成

bool                        YfBuildBoxVertices
(
    Yreal                   extentX,
    Yreal                   extentY,  
    Yreal                   extentZ, 
    YeOriginPose            originPose,
    Yuint                   vertexStriding,
    Yuint                   vertexPos,
    void*                   pVerticesBuffer
)
{
    if (!pVerticesBuffer)
    {
        return false;
    }

    Yuint numVertices = 8;

    // 顶点赋值
    char* vertexPtr = (char*)pVerticesBuffer + vertexPos;

    YsVector3* curVertexPtr   = NULL;
    YsVector3* curNormalPtr   = NULL;
    YsVector2* curTexcoordPtr = NULL;

    Yuint nOffset = 0;

    YsVector3 vOriginOffset(-extentX / 2, -extentY / 2, -extentZ / 2);
    if (originPose == YE_ORIGIN_POSE_TOP)
    {
        vOriginOffset.y = -extentY;
    }
    else if (originPose == YE_ORIGIN_POSE_BOTTOM)
    {
        vOriginOffset.y = 0.0f;
    }

    for (Yuint k = 0; k < 2; k++)
    {
        for (Yuint j = 0; j < 2; j++)
        {
            for (Yuint i = 0; i < 2; i++)
            {
                nOffset = (k*4 + j*2 + i) * vertexStriding;
                curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
                curVertexPtr->x = extentX*i + vOriginOffset.x;
                curVertexPtr->z = extentZ*j + vOriginOffset.z;
                curVertexPtr->y = extentY*k + vOriginOffset.y;
            }
        }
    }

    return true;
}  

三角形索引数据的生成

bool                        YfBuildBoxTriIndices
(
    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[12];
        for (Yuint i = 0; i < 12; i++)
        {
            triIndexPtr[i] = (YsTriIndex16*)(indexPtr + i * indexStriding);
        }

        // bottom
        triIndexPtr[0]->index0 = 0; triIndexPtr[0]->index1 = 1; triIndexPtr[0]->index2 = 3;
        triIndexPtr[1]->index0 = 0; triIndexPtr[1]->index1 = 3; triIndexPtr[1]->index2 = 2;

        // top                                                   
        triIndexPtr[10]->index0= 4; triIndexPtr[10]->index1= 6; triIndexPtr[10]->index2= 7;
        triIndexPtr[11]->index0= 4; triIndexPtr[11]->index1= 7; triIndexPtr[11]->index2= 5;

        // front side
        triIndexPtr[2]->index0 = 0; triIndexPtr[2]->index1 = 4; triIndexPtr[2]->index2 = 5;
        triIndexPtr[3]->index0 = 0; triIndexPtr[3]->index1 = 5; triIndexPtr[3]->index2 = 1;

        // back side
        triIndexPtr[4]->index0 = 2; triIndexPtr[4]->index1 = 3; triIndexPtr[4]->index2 = 7;
        triIndexPtr[5]->index0 = 2; triIndexPtr[5]->index1 = 7; triIndexPtr[5]->index2 = 6;

        // right side
        triIndexPtr[6]->index0 = 1; triIndexPtr[6]->index1 = 5; triIndexPtr[6]->index2 = 7;
        triIndexPtr[7]->index0 = 1; triIndexPtr[7]->index1 = 7; triIndexPtr[7]->index2 = 3;

        // left side                                                       
        triIndexPtr[8]->index0 = 0; triIndexPtr[8]->index1 = 2; triIndexPtr[8]->index2 = 6;
        triIndexPtr[9]->index0 = 0; triIndexPtr[9]->index1 = 6; triIndexPtr[9]->index2 = 4;
    }
    else
    {
        YsTriIndex32* triIndexPtr[12];
        for (Yuint i = 0; i < 12; i++)
        {
            triIndexPtr[i] = (YsTriIndex32*)(indexPtr + i * indexStriding);
        }

        // bottom
        triIndexPtr[0]->index0 = 0; triIndexPtr[0]->index1 = 1; triIndexPtr[0]->index2 = 3;
        triIndexPtr[1]->index0 = 0; triIndexPtr[1]->index1 = 3; triIndexPtr[1]->index2 = 2;

        // top                                                   
        triIndexPtr[10]->index0= 4; triIndexPtr[10]->index1= 6; triIndexPtr[10]->index2= 7;
        triIndexPtr[11]->index0= 4; triIndexPtr[11]->index1= 7; triIndexPtr[11]->index2= 5;

        // front side
        triIndexPtr[2]->index0 = 0; triIndexPtr[2]->index1 = 4; triIndexPtr[2]->index2 = 5;
        triIndexPtr[3]->index0 = 0; triIndexPtr[3]->index1 = 5; triIndexPtr[3]->index2 = 1;

        // back side
        triIndexPtr[4]->index0 = 2; triIndexPtr[4]->index1 = 3; triIndexPtr[4]->index2 = 7;
        triIndexPtr[5]->index0 = 2; triIndexPtr[5]->index1 = 7; triIndexPtr[5]->index2 = 6;

        // right side
        triIndexPtr[6]->index0 = 1; triIndexPtr[6]->index1 = 5; triIndexPtr[6]->index2 = 7;
        triIndexPtr[7]->index0 = 1; triIndexPtr[7]->index1 = 7; triIndexPtr[7]->index2 = 3;

        // left side                                                       
        triIndexPtr[8]->index0 = 0; triIndexPtr[8]->index1 = 2; triIndexPtr[8]->index2 = 6;
        triIndexPtr[9]->index0 = 0; triIndexPtr[9]->index1 = 6; triIndexPtr[9]->index2 = 4;
    }

    return true;
}  

线框索引数据的生成

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

    char* indexPtr = (char*)pWireIndicesBuffer + indexPos;
    if (indexType == YE_INDEX_16_BIT)
    {
        YsLineIndex16* lineIndexPtr[12];
        for (Yuint i = 0; i < 12; i++)
        {
            lineIndexPtr[i] = (YsLineIndex16*)(indexPtr + i * indexStriding);
        }

        // bottom
        lineIndexPtr[0]->index0 = 0; lineIndexPtr[0]->index1 = 1; 
        lineIndexPtr[1]->index0 = 0; lineIndexPtr[1]->index1 = 2; 
        lineIndexPtr[2]->index0 = 3; lineIndexPtr[2]->index1 = 1; 
        lineIndexPtr[3]->index0 = 3; lineIndexPtr[3]->index1 = 2; 

        // center
        lineIndexPtr[4]->index0 = 0; lineIndexPtr[4]->index1 = 4; 
        lineIndexPtr[5]->index0 = 1; lineIndexPtr[5]->index1 = 5; 
        lineIndexPtr[6]->index0 = 2; lineIndexPtr[6]->index1 = 6; 
        lineIndexPtr[7]->index0 = 3; lineIndexPtr[7]->index1 = 7; 
                                        
        // top                                               
        lineIndexPtr[8]->index0 = 4; lineIndexPtr[8]->index1 = 5; 
        lineIndexPtr[9]->index0 = 4; lineIndexPtr[9]->index1 = 6; 
        lineIndexPtr[10]->index0= 7; lineIndexPtr[10]->index1= 5; 
        lineIndexPtr[11]->index0= 7; lineIndexPtr[11]->index1= 6;    
    }
    else
    {
        YsLineIndex32* lineIndexPtr[12];
        for (Yuint i = 0; i < 12; i++)
        {
            lineIndexPtr[i] = (YsLineIndex32*)(indexPtr + i * indexStriding);
        }

        // bottom
        lineIndexPtr[0]->index0 = 0; lineIndexPtr[0]->index1 = 1; 
        lineIndexPtr[1]->index0 = 0; lineIndexPtr[1]->index1 = 2; 
        lineIndexPtr[2]->index0 = 3; lineIndexPtr[2]->index1 = 1; 
        lineIndexPtr[3]->index0 = 3; lineIndexPtr[3]->index1 = 2; 

        // center
        lineIndexPtr[4]->index0 = 0; lineIndexPtr[4]->index1 = 4; 
        lineIndexPtr[5]->index0 = 1; lineIndexPtr[5]->index1 = 5; 
        lineIndexPtr[6]->index0 = 2; lineIndexPtr[6]->index1 = 6; 
        lineIndexPtr[7]->index0 = 3; lineIndexPtr[7]->index1 = 7; 
                                        
        // top                                               
        lineIndexPtr[8]->index0 = 4; lineIndexPtr[8]->index1 = 5; 
        lineIndexPtr[9]->index0 = 4; lineIndexPtr[9]->index1 = 6; 
        lineIndexPtr[10]->index0= 7; lineIndexPtr[10]->index1= 5; 
        lineIndexPtr[11]->index0= 7; lineIndexPtr[11]->index1= 6;  
    }

    return true;
}