cocos2d-x中使图片背景全透明（另一种方法）

 CCLayerColor::initWithColor(ccc4(255,255,255,255));

         CCImage *pImage = new CCImage();
         pImage->autorelease();
         pImage->initWithImageFile("arraw.png",CCImage::EImageFormat::kFmtPng);

         //遍历图片的所有像素.
         unsigned char *pData = pImage->getData();
         int nPixelIndex = 0;
         for (int nCol = 0; nCol < pImage->getHeight(); nCol ++)
         {
             for (int nRow = 0; nRow < pImage->getWidth(); nRow ++)
             {
                 //取图片的RGB值.
                 int nBeginPos = nPixelIndex;
                 unsigned int nRValue = pData[nPixelIndex];
                 nPixelIndex++;
                 unsigned int nGValue = pData[nPixelIndex];
                 nPixelIndex ++;
                 unsigned int nBValue = pData[nPixelIndex];
                 nPixelIndex ++;
                 unsigned int nAValue = pData[nPixelIndex];
                 nPixelIndex ++;

                 int nAlphaRatio = 0;
                 //本代码的核心:取RGB中的最大值赋给nAlphaRatio。如果nAlphaRatio为0,则像素中的alpha通道就为0,否则像素中的
                 //alpha通道值就是nAlphaRatio。这样做是为了在图片中颜色渐变过渡比较大的区域实现平滑的过渡。让最终形成的
                 //图片看起来不粗糙.
                 nAlphaRatio = nRValue>nGValue?(nRValue>nBValue?nRValue:nBValue):(nGValue>nBValue?nGValue:nBValue);
                 if(nAlphaRatio != 0)
                 {
                     nAValue = nAlphaRatio;
                 }
                 else
                 {
                     nAValue= 0;
                 }

                 pData[nBeginPos] = (unsigned char)nRValue;
                 pData[nBeginPos+ 1] = (unsigned char)nGValue;
                 pData[nBeginPos + 2] = (unsigned char)nBValue;
                 //修改原图的alpha值.
                 pData[nBeginPos + 3] = (unsigned char)nAValue;
             }
         }

         CCTexture2D *pTexture = new CCTexture2D;
         pTexture->autorelease();
         pTexture->initWithImage(pImage);
         CCTexture2DPixelFormat ccpf = pTexture->getPixelFormat();
         CCAssert(ccpf == kTexture2DPixelFormat_RGBA8888, "your png file's pixel format is not RGBA8888 or not have alpha panel");

         CCSprite* pArrowSprite= new CCSprite();
         pArrowSprite->initWithTexture(pTexture);
         CCSize size = CCDirector::sharedDirector()->getWinSize();
         pArrowSprite->setPosition(ccp(size.width/2 + 20, size.height/2 - 20));
         this->addChild(pArrowSprite, 6);

直接看代码注释就懂了。贴上效果图，打完收工。