NV12剪切区域时的对齐代码

#define NV12_PACK 2
//如果没有对齐，NV12无法生成JPG，或者底边颜色异常。对齐时要避免剪切区域变小。
int clipNv12Pack(int* pnClipLeft, int* pnClipTop, int* pnClipWidth, int* pnClipHeight)
{
    const int clipLeft  = *pnClipLeft;
    const int clipTop   = *pnClipTop;
    const int clipWidth = *pnClipWidth;
    const int clipHeight= *pnClipHeight;
    if (*pnClipLeft % NV12_PACK != 0)
    {
        *pnClipLeft  = clipLeft/NV12_PACK*NV12_PACK;
        *pnClipWidth = clipWidth+(clipLeft-*pnClipLeft);
    }
    *pnClipWidth  = (*pnClipWidth+NV12_PACK-1)/NV12_PACK*NV12_PACK;
    if (*pnClipTop % NV12_PACK != 0)
    {
        *pnClipTop   = clipTop/NV12_PACK*NV12_PACK;
        *pnClipHeight= clipHeight+(clipTop-*pnClipTop);
    }
    *pnClipHeight = (*pnClipHeight+NV12_PACK-1)/NV12_PACK*NV12_PACK;
    return 0;
}