只显示CCLayer部分特定区域的方法

- (void) beforeDraw{
    glEnable(GL_SCISSOR_TEST);  
    const CGFloat s = [[CCDirector sharedDirector] contentScaleFactor];  
    const int w = 90, h = 111;
    glScissor(self.position.x *s + w,  
              self.position.y * s + h,  
              self.contentSize.width*s - 2*w,   
              self.contentSize.height*s - 2*h);  
}

- (void) afterDraw{
    glDisable(GL_SCISSOR_TEST); 
}

- (void) visit{
    // quick return if not visible
    if (!visible_)
        return;
    
    glPushMatrix();
    
    if ( grid_ && grid_.active) {
        [grid_ beforeDraw];
        [self transformAncestors];
    }
    
    [self transform];
    
    [self beforeDraw];
    
    if(children_) {
        ccArray *arrayData = children_->data;
        NSUInteger i = 0;
        
        // draw children zOrder < 0
        for( ; i < arrayData->num; i++ ) {
            CCNode *child = arrayData->arr[i];
            if ( [child zOrder] < 0 )
                [child visit];
            else
                break;
        }
        
        // self draw
        [self draw];
        
        // draw children zOrder >= 0
        for( ; i < arrayData->num; i++ ) {
            CCNode *child =  arrayData->arr[i];
            [child visit];
        }
        
    } else
        [self draw];
    
    [self afterDraw];
    
    if ( grid_ && grid_.active)
        [grid_ afterDraw:self];
    
    glPopMatrix();
}

在CCLayer中，负责绘制的函数是在visit函数中，所以我们需要将这个函数重写。

修改- (void) beforeDraw中glScissor函数的参数即可改变显示的区域位置

参考：http://blog.csdn.net/tangaowen/article/details/7539536