如何在IOS中应用部分淡入淡出? [英] How to apply partial fade in-out in IOS?
问题描述
我有2张图片。一个在另一个的后面。我想从左角开始淡出顶部图像。我怎样才能做到这一点?
I have 2 images. One is in the back of the other. I want to fade-out the top image starting from the left corner. How can I do this?
我应该使用渐变掩码吗?
Should I use gradient mask?
推荐答案
这是一种技术将从左上角到右下角淡出CALayer中的任何内容,揭示CALayer下面的任何内容。
Here's a technique that will fade out whatever's in a CALayer, from top-left to bottom-right, revealing whatever is underneath the CALayer.
假设我们将淡出图层一个 UIImageView
名为 self.fadeView
。
Let's say we're going to fade out the layer of a UIImageView
called self.fadeView
.
我们'll创建一个 CAGradientLayer
并将其用作 self.fadeView.layer.mask
。渐变将使用四个停止点从alpha = 0(透明)到alpha = 1(不透明):0,0,1,1。是,两个零,然后是两个。当我们希望 fadeView
不透明时,我们将停止位置设置为-1,-.5,0,1。这样两个alpha = 0的停止就完全了在图层边界之外。当我们希望 fadeView
是透明的时,我们将停止位置设置为0,1,1.5,2。这样两个alpha = 1的停止位置完全在图层边界。 CAGradientLayer
会自动为其停止位置设置动画,从而产生交叉渐变效果。
We'll create a CAGradientLayer
and use it as self.fadeView.layer.mask
. The gradient will go from alpha=0 (transparent) to alpha=1 (opaque) using four stops: 0, 0, 1, 1. Yes, two zeros and then two ones. When we want fadeView
to be opaque, we'll set the stop locations to -1, -.5, 0, 1. That way the two alpha=0 stops are completely outside of the layer bounds. When we want fadeView
to be transparent, we'll set the stop locations to 0, 1, 1.5, 2. That way the two alpha=1 stops are completely outside of the layer bounds. The CAGradientLayer
will automatically animate changes to its stop locations, creating a cross-fade effect.
以下是代码:
#import "ViewController.h"
@implementation ViewController
@synthesize fadeView = _fadeView;
static NSArray *locations(float a, float b, float c, float d)
{
return [NSArray arrayWithObjects:
[NSNumber numberWithFloat:a],
[NSNumber numberWithFloat:b],
[NSNumber numberWithFloat:c],
[NSNumber numberWithFloat:d],
nil];
}
// In my test project, I put a swipe gesture recognizer on fadeView in my XIB
// with direction = Up and connected it to this action.
- (IBAction)fadeIn
{
[CATransaction begin];
[CATransaction setValue:[NSNumber numberWithDouble:2.0] forKey:kCATransactionAnimationDuration];
((CAGradientLayer *)self.fadeView.layer.mask).locations = locations(-1, -.5, 0, 1);
[CATransaction commit];
}
// In my test project, I put a swipe gesture recognizer on fadeView in my XIB
// with direction = Down and connected it to this action.
- (IBAction)fadeOut
{
[CATransaction begin];
[CATransaction setValue:[NSNumber numberWithDouble:2.0] forKey:kCATransactionAnimationDuration];
((CAGradientLayer *)self.fadeView.layer.mask).locations = locations(0, 1, 1.5, 2);
[CATransaction commit];
}
- (void)viewDidLoad
{
[super viewDidLoad];
CAGradientLayer *mask = [CAGradientLayer layer];
mask.frame = self.fadeView.bounds;
mask.colors = [NSArray arrayWithObjects:
(__bridge id)[UIColor clearColor].CGColor,
(__bridge id)[UIColor clearColor].CGColor,
(__bridge id)[UIColor whiteColor].CGColor,
(__bridge id)[UIColor whiteColor].CGColor,
nil];
mask.startPoint = CGPointZero; // top left corner
mask.endPoint = CGPointMake(1, 1); // bottom right corner
self.fadeView.layer.mask = mask;
[self fadeIn]; // initialize mask.locations
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
// Return YES for supported orientations
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
}
@end
这篇关于如何在IOS中应用部分淡入淡出?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!