cocos2d-x 手电筒效果

常见的手电筒效果，可以通过CCRenderTexture来实现。主要是通过修改渲染表面的alpha值来达到手电筒光照范围内的透明效果。此方法纯原创，如有雷同，英雄所见略同。这里由于本人没有什么图片，这里直接用矩形区域来代替圆形区域。通过以下几个基本步骤来完成这个效果。

1. 首先创建一个全黑的渲染表明覆盖在场景之上。
   

       //create render target
       CCRenderTexture* pRenderTexture = CCRenderTexture::create( BY_WIN_SIZE_WIDTH, BY_WIN_SIZE_HEIGHT );
       
       //render the target to black
       pRenderTexture->begin();
       glDisable( GL_BLEND );
       ccDrawSolidRect( ccp( 0, 0 ), ccp( BY_WIN_SIZE_WIDTH, BY_WIN_SIZE_HEIGHT ), ccc4f( 0, 0, 0, 1 ) );
       glEnable( GL_BLEND );
       pRenderTexture->end();
       
       //set the render target over the scene
       pRenderTexture->setPosition( ccp( BY_WIN_SIZE_WIDTH_HALF, BY_WIN_SIZE_HEIGHT_HALF ) );
       addChild( pRenderTexture, 2, 1000 );
       
       //render target is the sprite's texture.
       //set the sprite render parms.
       ccBlendFunc bf = { GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA };
       pRenderTexture->getSprite()->setBlendFunc( bf );
   

2. 在ccTouchBegan()函数中透明处用户点击的区域
   

       //get transparent area
       CCPoint ptBottomLeftCorner = ccpSub( pTouch->getLocation(), ccp( 200, 200 ) );
       CCPoint ptTopRightCorner = ccpAdd( pTouch->getLocation(), ccp( 200, 200 ) );
       
       //set the area transparent
       BY_GET_CHILD( CCRenderTexture, 1000 )->begin();
       glDisable( GL_BLEND );
       ccDrawSolidRect( ptBottomLeftCorner, ptTopRightCorner, ccc4f( 0, 0, 0, 0 ) );
       glEnable( GL_BLEND );
       BY_GET_CHILD( CCRenderTexture, 1000 )->end();

3. 在ccTouchMoved()函数中，首先抹黑原来的区域（这里为了保险，我们直接抹黑整个渲染表面），另外透明出新的区域
   

       //get transparent area
       CCPoint ptBottomLeftCorner = ccpSub( pTouch->getLocation(), ccp( 200, 200 ) );
       CCPoint ptTopRightCorner = ccpAdd( pTouch->getLocation(), ccp( 200, 200 ) );
       
       BY_GET_CHILD( CCRenderTexture, 1000 )->begin();
       glDisable( GL_BLEND );
       
       //set the render target black
       ccDrawSolidRect( CCPointZero, ccp( BY_WIN_SIZE_WIDTH, BY_WIN_SIZE_HEIGHT ), ccc4f( 0, 0, 0, 1 ) );
       //set the new area transparent
       ccDrawSolidRect( ptBottomLeftCorner, ptTopRightCorner, ccc4f( 0, 0, 0, 0 ) );
       
       glEnable( GL_BLEND );
       BY_GET_CHILD( CCRenderTexture, 1000 )->end();
   

4. 在ccTouchEnded()和ccTouchCanceled()函数中，抹黑整块渲染表面。
   

       BY_GET_CHILD( CCRenderTexture, 1000 )->begin();
       glDisable( GL_BLEND );
       ccDrawSolidRect( CCPointZero, ccp( BY_WIN_SIZE_WIDTH, BY_WIN_SIZE_HEIGHT ), ccc4f( 0, 0, 0, 1 ) );
       glEnable( GL_BLEND );
       BY_GET_CHILD( CCRenderTexture, 1000 )->end();