ARC下重写setter和getter方法

@synthesizeclearColor =_clearColor;

-(void)setClearColor:(GLKVector4)clearColor

{

_clearColor= clearColor;

NSAssert(self== [[selfclass]currentContext],@"Receiving context required to be current context");

glClearColor(clearColor.r, clearColor.g, clearColor.b, clearColor.a);

}

-(GLKVector4)clearColor

{

return_clearColor;

}