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 n***alue = 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)

{

n***alue = nAlphaRatio;

}

else

{

n***alue= 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)n***alue;

}

}

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。