Making a hole on a CCRenderTexture

Question

I am trying to make a hole on a CCRenderTexture with Cocos2D 2.0.

More specifically I have:

1. a CCSprite "stars" that shows some stars repeating a png image;
2. 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.