Making a hole on a CCRenderTexture - cocos2d-iphone

Question

I am trying to make a hole on a CCRenderTexture with Cocos2D 2.0.
More specifically I have:
a CCSprite "stars" that shows some stars repeating a png image;
on top of that I have a CCRenderTexture "dark" that completely covers the "stars" sprite.
I want to be able to cut a hole on "dark" in order to show the stars below.
I am using CCRenderTexture (as suggested in some tutorials) but the hole I manage to make is never fully transparent, so the stars visible through the hole are partially obscured.
I really hope some one can show me the light, I spent over a week on this...
This is the code:
#interface MyBackgroundLayer : CCLayerGradient {
}
#end
#implementation MyBackgroundLayer
CCRenderTexture * dark;
CCSprite * stars;
-(id) init
{
if (self=[super init]) {
CGSize size = [[CCDirector sharedDirector] winSize];
// background
stars = [CCSprite spriteWithFile:#"stars.png" rect:CGRectMake(0, 0, size.width, size.height)];
stars.anchorPoint = ccp(0,0);
ccTexParams params = {GL_LINEAR,GL_LINEAR,GL_REPEAT,GL_REPEAT};
[stars.texture setTexParameters:&params];
[self addChild:stars];
// dark layer to cover the background
dark = [CCRenderTexture renderTextureWithWidth:size.width height:size.height];
[dark clear:0 g:0 b:0 a:1.0f];
[self addChild: dark];
dark.position = ccp(size.width/2,size.height/2);
[[dark sprite] setBlendFunc: (ccBlendFunc) { GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA }];
}
return self;
}
-(void)draw
{
[super draw];
[dark beginWithClear:0 g:0 b:0 a:1];
glColorMask(0, 0, 0, 1);
// Here I am using 0.5 as alpha value, this could seems the reason why the hole is not fully transparent.
// However if I change the alpha value to 1.0f or 0.0f the hole becomes completely opaque
ccColor4F color = ccc4f(1.f, 1.f, 1.f, 0.5f);
ccDrawSolidRect(ccp(0,0), ccp(600, 600), color);
glColorMask(1,1,1,1);
[dark end];
}
#end

Answer 1

I think what you're looking for is something like this ( may need some editing).
As for your code ..i thing the problem is in the blend function. Check this out to see how they work.