[9] 圆环(Ring)图形的生成算法

顶点数据的生成

bool                        YfBuildRingVertices
(
    Yreal                   radius, 
    Yreal                   assistRadius, 
    Yreal                   height, 
    Yuint                   slices,
    Yuint                   stacks, 
    YeOriginPose            originPose,
    Yuint                   vertexStriding, 
    Yuint                   vertexPos,
    void*                   pVerticesBuffer
)
{
    if (slices < 2 || stacks < 3 || !pVerticesBuffer)
    {
        return false;
    }

    Yuint numVertices  = slices * stacks;
    Yuint numTriangles = slices * stacks * 2;

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

    Yreal halfHeight = height * 0.5f;
    Yreal originOffsetY = 0.0f;
    if (originPose == YE_ORIGIN_POSE_TOP)
    {
        originOffsetY = -halfHeight;
    }
    else if (originPose == YE_ORIGIN_POSE_BOTTOM)
    {
        originOffsetY = halfHeight;
    }

    Yreal angle, s, c;
    YsVector3* initVerticesPtr = new YsVector3[slices + 1];
    for (Yuint j = 0; j < slices; j++)
    {
        angle = YD_REAL_TWAIN_PI * j / slices;
        s = yf_sin(angle);
        c = yf_cos(angle);
        initVerticesPtr[j].x = radius + assistRadius*s;
        initVerticesPtr[j].y = halfHeight*c + originOffsetY;
        initVerticesPtr[j].z = 0.0f;
    }

    for (Yuint i = 0; i < stacks; i++)
    {
        angle = YD_REAL_TWAIN_PI * i / stacks;
        s = yf_sin(angle);
        c = yf_cos(angle);

        for (Yuint j = 0; j < slices; j++)
        {
            nOffset = (i * slices + j) * vertexStriding; 
            curVertexPtr = (YsVector3*)(vertexPtr + nOffset);
            curVertexPtr->x = initVerticesPtr[j].x * s;
            curVertexPtr->y = initVerticesPtr[j].y;
            curVertexPtr->z = initVerticesPtr[j].x * c;
        }
    }

    YD_SAFE_DELETE_ARRAY(initVerticesPtr);

    return true;
}     

三角形索引数据的生成

bool                        YfBuildRingTriIndices
(
    Yuint                   slices,
    Yuint                   stacks,
    YeIndexType             indexType,
    Yuint                   indexStriding,  
    Yuint                   indexPos,
    void*                   pTriIndicesBuffer
)
{
    if (slices < 2 || stacks < 3 || !pTriIndicesBuffer)
    {
        return false;
    }

    Yuint numVertices  = slices * stacks;
    Yuint numTriangles = slices * stacks * 2;
    if (indexType == YE_INDEX_16_BIT && 
        numVertices > YD_MAX_UNSIGNED_INT16)
    {
        return false;
    }

    // 索引赋值
    char* indexPtr = (char*)pTriIndicesBuffer + indexPos;
    Yuint nOffset = 0;
    if (indexType == YE_INDEX_16_BIT)
    {
        YsTriIndex16* triIndexPtr = NULL;
        for (Yuint i = 0; i < stacks; i++)
        {
            for (Yuint j = 0; j < slices; j++)
            {
                nOffset = (i*slices + j)*2 * indexStriding;
                triIndexPtr = (YsTriIndex16*)(indexPtr + nOffset);
                triIndexPtr->index0 = slices * i + j;
                triIndexPtr->index1 = slices * i + (j + 1)%slices;
                triIndexPtr->index2 = slices * ((i + 1) % stacks) + j;

                nOffset += indexStriding;
                triIndexPtr = (YsTriIndex16*)(indexPtr + nOffset);
                triIndexPtr->index0 = slices * i + (j + 1)%slices;
                triIndexPtr->index1 = slices * ((i + 1) % stacks) + (j + 1)%slices;
                triIndexPtr->index2 = slices * ((i + 1) % stacks) + j;
            }
        }
    }
    else
    {
        YsTriIndex32* triIndexPtr = NULL;
        for (Yuint i = 0; i < stacks; i++)
        {
            for (Yuint j = 0; j < slices; j++)
            {
                nOffset = (i*slices + j)*2 * indexStriding;
                triIndexPtr = (YsTriIndex32*)(indexPtr + nOffset);
                triIndexPtr->index0 = slices * i + j;
                triIndexPtr->index1 = slices * i + (j + 1)%slices;
                triIndexPtr->index2 = slices * ((i + 1) % stacks) + j;

                nOffset += indexStriding;
                triIndexPtr = (YsTriIndex32*)(indexPtr + nOffset);
                triIndexPtr->index0 = slices * i + (j + 1)%slices;
                triIndexPtr->index1 = slices * ((i + 1) % stacks) + (j + 1)%slices;
                triIndexPtr->index2 = slices * ((i + 1) % stacks) + j;
            }
        }
    }

    return true;
}   

线框索引数据的生成

bool                        YfBuildRingWireIndices
(
    Yuint                   slices,
    Yuint                   stacks,
    YeIndexType             indexType,
    Yuint                   indexStriding,  
    Yuint                   indexPos,
    void*                   pWireIndicesBuffer
)
{
    if (slices < 2 || !pWireIndicesBuffer)
    {
        return false;
    }

    Yuint numVertices = slices * stacks;
    Yuint numLines    = slices * stacks * 2;
    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;
        for (Yuint i = 0; i < stacks; i++)
        {
            for (Yuint j = 0; j < slices; j++)
            {
                nOffset = (i*slices + j) * 2 * indexStriding;
                lineIndexPtr = (YsLineIndex16*)(indexPtr + nOffset);
                lineIndexPtr->index0 = slices * i + j;
                lineIndexPtr->index1 = slices * i + (j + 1)%slices;

                nOffset += indexStriding;
                lineIndexPtr = (YsLineIndex16*)(indexPtr + nOffset);
                lineIndexPtr->index0 = slices * i + j;
                lineIndexPtr->index1 = slices * ((i + 1) % stacks) + j;
            }
        }
    }
    else
    {
        YsLineIndex32* lineIndexPtr = NULL;
        for (Yuint i = 0; i < stacks; i++)
        {
            for (Yuint j = 0; j < slices; j++)
            {
                nOffset = (i*slices + j) * 2 * indexStriding;
                lineIndexPtr = (YsLineIndex32*)(indexPtr + nOffset);
                lineIndexPtr->index0 = slices * i + j;
                lineIndexPtr->index1 = slices * i + (j + 1)%slices;

                nOffset += indexStriding;
                lineIndexPtr = (YsLineIndex32*)(indexPtr + nOffset);
                lineIndexPtr->index0 = slices * i + j;
                lineIndexPtr->index1 = slices * ((i + 1) % stacks) + j;
            }
        }
    }

    return true;
}