How to make vignette effect on iOS?

Question

When the UIAlertViews message appears, a vignette effect is applied in the background. That is, the edges are darker and the center is lighter.

I was wondering if this vignette effect was built into Cocoa Touch. I would like to show a vignette for one of my custom views.

Answer 1

It is built into UIKit (since UIAlertView is part of UIKit), but it is not publicly available.

However, it should not be too difficult to create the same effect. This is just a radial gradient that you can use in code or in Photoshop.

: , - _UIAlertNormalizingOverlayWindow :

_UIAlertNormalizingOverlayWindow
_UIAlertOverlayWindow
UIWindow

Answer 2

- uialertview . , . ,

Answer 3

VignetteEffect UIView

-drawRect::

- (void)drawRect:(CGRect)rect
{

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGColorSpaceRef colSp = CGColorSpaceCreateDeviceRGB();

    CGGradientRef gradient = CGGradientCreateWithColors(colSp, (__bridge CFArrayRef)[NSArray arrayWithObjects:(id)[[UIColor colorWithRed:0 green:0 blue:0 alpha:0] CGColor], (id)[[UIColor colorWithRed:0 green:0 blue:0 alpha:0.5] CGColor], nil], 0);

    CGContextDrawRadialGradient(context, gradient, self.center, 0, self.center, self.frame.size.height+self.frame.size.height/4, 0);

    CGColorSpaceRelease(colSp);
    CGGradientRelease(gradient);

}

.

, . . .

Answer 4

SVProgressHud , , SVProgressHUDMaskTypeGradient.

Answer 5

I dispute the selected answer is incorrect and potentially dangerous. Here is my solution:

I copied the gradient drawing code from SVProgressHud into my fork from SSGradientView:

SSGradientView *vignette = [SSGradientView new];
vignette.frame = [UIScreen mainScreen].currentBounds;
vignette.backgroundColor = [UIColor clearColor];
vignette.direction = SSGradientViewDirectionRadial;
UIColor *startColor = // We just need the colorspace.
UIColor *endColor = // Visible vignette color.
vignette.colors = @[
[startColor colorWithAlphaComponent:0.0f], 
[endColor colorWithAlphaComponent:1.0f] ];
vignette.locations = @[ @0.4f, @1.0f ];
[view insertSubview:vignette atIndex:0]; // Or equivalent.