最近研究了一下像素级的触摸处理，有时候我们用一个不规则的图形作为一个按钮，这个不规则的图形是一张矩形的png图片，很可能图片的实际有效的显示内容只占整个png图片的很小一部分，剩下的大部分都是png图片的透明区域，我们想把这部分透明区域过滤掉，实现一个触摸到真实的内容才会有按钮响应的效果。

刚开始试图通过CCSprite直接获取到纹理的像素信息，但是cocos2d-x并没有给我们提供直接通过CCSprite获取像素信息的接口，研究了几个网上的Demo，发现通过使用RenderTexture重绘可以实现这一效果，下面把代码贴出来。

#include "HelloWorldScene.h"
#include "SimpleAudioEngine.h"

using namespace cocos2d;
using namespace CocosDenshion;

CCScene* HelloWorld::scene()
{
    // 'scene' is an autorelease object
    CCScene *scene = CCScene::create();
    
    // 'layer' is an autorelease object
    HelloWorld *layer = HelloWorld::create();

    // add layer as a child to scene
    scene->addChild(layer);

    // return the scene
    return scene;
}

bool HelloWorld::init()
{
    if (!CCLayer::init()){
        return false;
    }
    
    this->setTouchEnabled(true);

    this->m_imgMan = CCSprite::create("man.png");
    this->m_imgMan->setPosition(ccp(400, 200));
    this->addChild(this->m_imgMan, 1);
    
    this->m_pRenderTexture = CCRenderTexture::create(this->m_imgMan->getContentSize().width, this->m_imgMan->getContentSize().height, kCCTexture2DPixelFormat_RGBA8888);
    this->m_pRenderTexture->ignoreAnchorPointForPosition(true);
    this->m_pRenderTexture->setPosition(ccp(400, 200));
    this->m_pRenderTexture->setAnchorPoint(CCPointZero);
    this->addChild(this->m_pRenderTexture, 0, 1);

    
    return true;
}

bool HelloWorld::ccTouchBegan(cocos2d::CCTouch *pTouch, cocos2d::CCEvent *pEvent) {
    
    bool isTouched = false;
    
    CCPoint touchPoint = pTouch->getLocationInView();
    CCPoint glPoint = CCDirector::sharedDirector()->convertToGL(touchPoint);


    if (this->m_imgMan->boundingBox().containsPoint(glPoint)) {
    
        ccColor4B color4B = {0, 0, 0, 0};
        
        CCPoint nodePos = this->m_imgMan->convertTouchToNodeSpace(pTouch);
        unsigned int x = nodePos.x;
        unsigned int y = this->m_imgMan->getContentSize().height - nodePos.y;
        
        CCPoint point = this->m_imgMan->getPosition();
        //开始准备绘制
        this->m_pRenderTexture->begin();
        //绘制使用的临时精灵，与原图是同一图片
        CCSprite* pTempSpr = CCSprite::createWithSpriteFrame(this->m_imgMan->displayFrame());
        pTempSpr->setPosition(ccp(pTempSpr->getContentSize().width / 2, pTempSpr->getContentSize().height / 2));
        //绘制
        pTempSpr->visit();
        //结束绘制
        this->m_pRenderTexture->end();
        //通过画布拿到这张画布上每个像素点的信息，封装到CCImage中
        CCImage* pImage = this->m_pRenderTexture->newCCImage();
        //获取像素数据
        unsigned char* data_ = pImage->getData();
        unsigned int *pixel = (unsigned int *)data_;
        pixel = pixel + (y * (int)pTempSpr->getContentSize().width) * 1 + x * 1;
        //R通道
        color4B.r = *pixel & 0xff;
        //G通道
        color4B.g = (*pixel >> 8) & 0xff;
        //B通过
        color4B.b = (*pixel >> 16) & 0xff;
        //Alpha通道，我们有用的就是Alpha
        color4B.a = (*pixel >> 24) & 0xff;
        
        CCLOG("当前点击的点的: alpha = %d", color4B.a);
        
        if (color4B.a > 50) {
            isTouched = true;
        } else {
            isTouched = false;
        }
        
        //绘制完成后清理画布的内容
        this->m_pRenderTexture->clear(0, 0, 0, 0);
    }
    
    
    if (this->m_pLabTips) {
        this->m_pLabTips->removeFromParentAndCleanup(true);
        this->m_pLabTips = NULL;
    }
    
    return isTouched;
}


void HelloWorld::ccTouchEnded(cocos2d::CCTouch *pTouch, cocos2d::CCEvent *pEvent) {
    
    if (this->m_pLabTips) {
        this->m_pLabTips->removeFromParentAndCleanup(true);
        this->m_pLabTips = NULL;
    }
    
    this->m_pLabTips = CCLabelTTF::create("点击到非透明的像素点", "Courier", 30);
    this->m_pLabTips->setAnchorPoint(CCPointZero);
    this->m_pLabTips->setPosition(ccp(300.0f, 100.0f));
    this->m_pLabTips->setColor(ccYELLOW);
    this->addChild(this->m_pLabTips, 1);

}

void HelloWorld::registerWithTouchDispatcher() {
    CCDirector::sharedDirector()->getTouchDispatcher()->addTargetedDelegate(this, CCLayer::getTouchPriority(), false);
}

当点击到了透明的黑色区域时，屏幕上不显示任何文字，观察打印日志信息：

cocos2d-x像素级触摸处理