Add a magnifier in cocos2d games

i want to add a magnifier in cocos2d game. here is what i found online: http://coffeeshopped.com/2010/03/a-simpler-magnifying-glass-loupe-view-for-the-iphone I've change开发者_如何学运维d the code a bit:(since i don't want to let the loupe follow our touch)

- (id)initWithFrame:(CGRect)frame {
if ((self = [super initWithFrame:magnifier_rect])) {
    // make the circle-shape outline with a nice border.
    self.layer.borderColor = [[UIColor lightGrayColor] CGColor];
    self.layer.borderWidth = 3;
    self.layer.cornerRadius = 250;
    self.layer.masksToBounds = YES;
    touchPoint = CGPointMake(CGRectGetMidX(magnifier_rect), CGRectGetMidY(magnifier_rect));
}
return self;
}

Then i want to add it in one of my scene init method:

    loop = [[MagnifierView alloc] init];
    [loop setNeedsDisplay];
    loop.viewToMagnify = [CCDirector sharedDirector].openGLView;

    [[CCDirector sharedDirector].openGLView.superview addSubview:loop];

But the result is: the area inside the loupe is black. Also this loupe just magnify images with the same scale, how can i change it to magnify more near the center and less near the edge? (just like real magnifier) Thank you !!!

Here I assume that you want to magnify the center of the screen.

You have to change dynamically size attribute to your wishes according to your app needs.

CGSize size = [[CCDirector sharedDirector] winSize];

id lens = [CCLens3D actionWithPosition:ccp(size.width/2,size.height/2) radius:240 grid:ccg(15,10) duration:0.0f]; 

[self runAction:lens];

Cocos2d draws using OpenGL, not CoreAnimation/Quartz. The CALayer you are drawing is empty, so you see nothing. You will either have to use OpenGL graphics code to perform the loupe effect or sample the pixels and alter them appropriately to achieve the magnification effect, as was done in the Christmann article referenced from the article you linked to. That code also relies on CoreAnimation/Quartz, so you will need to work out another way to get your hands on the image data you wish to magnify.