目录
前言
在讲述AV Foundation框架之媒体捕捉。我将用一个小案例来开始整个知识点的引导以及疏通。我就不一一赘述相关的UI实现了。关于UI搭建部分，同学们可以在本篇文章末尾拿到百度网盘分享。你就可以在这个基础上进行编码了。
创建预览视图
下图是项目的用户界面的组成图示。我们把重点放在中间层THPreview View的实现上。因为它直接包含了AV Foundation 的用户界面。
图所示的THPreview View 类提供给用户用i 个摄像头当前拍摄内容的实时预览图。我们将使用AVCaptureVideoPreviewLayer方法实现这个行为。首先我们通过认识THPreview View 的接口开始了解如何实现。
一、THPreviewView 接口
#import <AVFoundation/AVFoundation.h>
@protocol THPreviewViewDelegate <NSObject>
- (void)tappedToFocusAtPoint:(CGPoint)point;//聚焦
- (void)tappedToExposeAtPoint:(CGPoint)point;//曝光
- (void)tappedToResetFocusAndExposure;//点击重置聚焦&曝光
@end
@interface THPreviewView : UIView
//session用来关联AVCaptureVideoPreviewLayer 和 激活AVCaptureSession
@property (strong, nonatomic) AVCaptureSession *session;
@property (weak, nonatomic) id<THPreviewViewDelegate> delegate;
@property (nonatomic) BOOL tapToFocusEnabled; //是否聚焦
@property (nonatomic) BOOL tapToExposeEnabled; //是否曝光
@end
二、 THPreviewView 实现
#import "THPreviewView.h"
#import "NSTimer+Additions.h"
#define BOX_BOUNDS CGRectMake(0.0f, 0.0f, 150, 150.0f)
@interface THPreviewView ()
@property (strong, nonatomic) UIView *focusBox;
@property (strong, nonatomic) UIView *exposureBox;
@property (strong, nonatomic) NSTimer *timer;
@property (strong, nonatomic) UITapGestureRecognizer *singleTapRecognizer;
@property (strong, nonatomic) UITapGestureRecognizer *doubleTapRecognizer;
@property (strong, nonatomic) UITapGestureRecognizer *doubleDoubleTapRecognizer;
@end
@implementation THPreviewView
- (id)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
[self setupView];
}
return self;
}
- (id)initWithCoder:(NSCoder *)coder {
self = [super initWithCoder:coder];
if (self) {
[self setupView];
}
return self;
}
+ (Class)layerClass {
//在UIView 重写layerClass 类方法可以让开发者创建视图实例自定义图层了下
//重写layerClass方法并返回AVCaptureVideoPrevieLayer类对象
return [AVCaptureVideoPreviewLayer class];
}
- (AVCaptureSession*)session {
//重写session方法，返回捕捉会话
return [(AVCaptureVideoPreviewLayer*)self.layer session];
}
- (void)setSession:(AVCaptureSession *)session {
//重写session属性的访问方法，在setSession:方法中访问视图layer属性。
//AVCaptureVideoPreviewLayer 实例，并且设置AVCaptureSession 将捕捉数据直接输出到图层中，并确保与会话状态同步。
[(AVCaptureVideoPreviewLayer*)self.layer setSession:session];
}
//关于UI的实现，例如手势，单击、双击 单击聚焦、双击曝光
- (void)setupView {
[(AVCaptureVideoPreviewLayer *)self.layer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
_singleTapRecognizer =
[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleSingleTap:)];
_doubleTapRecognizer =
[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleDoubleTap:)];
_doubleTapRecognizer.numberOfTapsRequired = 2;
_doubleDoubleTapRecognizer =
[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleDoubleDoubleTap:)];
_doubleDoubleTapRecognizer.numberOfTapsRequired = 2;
_doubleDoubleTapRecognizer.numberOfTouchesRequired = 2;
[self addGestureRecognizer:_singleTapRecognizer];
[self addGestureRecognizer:_doubleTapRecognizer];
[self addGestureRecognizer:_doubleDoubleTapRecognizer];
[_singleTapRecognizer requireGestureRecognizerToFail:_doubleTapRecognizer];
_focusBox = [self viewWithColor:[UIColor colorWithRed:0.102 green:0.636 blue:1.000 alpha:1.000]];
_exposureBox = [self viewWithColor:[UIColor colorWithRed:1.000 green:0.421 blue:0.054 alpha:1.000]];
[self addSubview:_focusBox];
[self addSubview:_exposureBox];
}
- (void)handleSingleTap:(UIGestureRecognizer *)recognizer {
CGPoint point = [recognizer locationInView:self];
[self runBoxAnimationOnView:self.focusBox point:point];
if (self.delegate) {
[self.delegate tappedToFocusAtPoint:[self captureDevicePointForPoint:point]];
}
}
//私有方法 用于支持该类定义的不同触摸处理方法。 将屏幕坐标系上的触控点转换为摄像头上的坐标系点
- (CGPoint)captureDevicePointForPoint:(CGPoint)point {
AVCaptureVideoPreviewLayer *layer =
(AVCaptureVideoPreviewLayer *)self.layer;
return [layer captureDevicePointOfInterestForPoint:point];
}
- (void)handleDoubleTap:(UIGestureRecognizer *)recognizer {
CGPoint point = [recognizer locationInView:self];
[self runBoxAnimationOnView:self.exposureBox point:point];
if (self.delegate) {
[self.delegate tappedToExposeAtPoint:[self captureDevicePointForPoint:point]];
}
}
- (void)handleDoubleDoubleTap:(UIGestureRecognizer *)recognizer {
[self runResetAnimation];
if (self.delegate) {
[self.delegate tappedToResetFocusAndExposure];
}
}
- (void)runBoxAnimationOnView:(UIView *)view point:(CGPoint)point {
view.center = point;
view.hidden = NO;
[UIView animateWithDuration:0.15f
delay:0.0f
options:UIViewAnimationOptionCurveEaseInOut
animations:^{
view.layer.transform = CATransform3DMakeScale(0.5, 0.5, 1.0);
}
completion:^(BOOL complete) {
double delayInSeconds = 0.5f;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
view.hidden = YES;
view.transform = CGAffineTransformIdentity;
});
}];
}
- (void)runResetAnimation {
if (!self.tapToFocusEnabled && !self.tapToExposeEnabled) {
return;
}
AVCaptureVideoPreviewLayer *previewLayer = (AVCaptureVideoPreviewLayer *)self.layer;
CGPoint centerPoint = [previewLayer pointForCaptureDevicePointOfInterest:CGPointMake(0.5f, 0.5f)];
self.focusBox.center = centerPoint;
self.exposureBox.center = centerPoint;
self.exposureBox.transform = CGAffineTransformMakeScale(1.2f, 1.2f);
self.focusBox.hidden = NO;
self.exposureBox.hidden = NO;
[UIView animateWithDuration:0.15f
delay:0.0f
options:UIViewAnimationOptionCurveEaseInOut
animations:^{
self.focusBox.layer.transform = CATransform3DMakeScale(0.5, 0.5, 1.0);
self.exposureBox.layer.transform = CATransform3DMakeScale(0.7, 0.7, 1.0);
}
completion:^(BOOL complete) {
double delayInSeconds = 0.5f;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
self.focusBox.hidden = YES;
self.exposureBox.hidden = YES;
self.focusBox.transform = CGAffineTransformIdentity;
self.exposureBox.transform = CGAffineTransformIdentity;
});
}];
}
- (void)setTapToFocusEnabled:(BOOL)enabled {
_tapToFocusEnabled = enabled;
self.singleTapRecognizer.enabled = enabled;
}
- (void)setTapToExposeEnabled:(BOOL)enabled {
_tapToExposeEnabled = enabled;
self.doubleTapRecognizer.enabled = enabled;
}
- (UIView *)viewWithColor:(UIColor *)color {
UIView *view = [[UIView alloc] initWithFrame:BOX_BOUNDS];
view.backgroundColor = [UIColor clearColor];
view.layer.borderColor = color.CGColor;
view.layer.borderWidth = 5.0f;
view.hidden = YES;
return view;
}
@end
坐标空间转换
//私有方法 用于支持该类定义的不同触摸处理方法。 将屏幕坐标系上的触控点转换为摄像头上的坐标系点
- (CGPoint)captureDevicePointForPoint:(CGPoint)point {
AVCaptureVideoPreviewLayer *layer =
(AVCaptureVideoPreviewLayer *)self.layer;
return [layer captureDevicePointOfInterestForPoint:point];
}
当使用AV Foundation 的捕捉API时，一定要理解屏幕坐标系和捕捉设备坐标系不同。iOS6.0之前的版本，要在这2个坐标空间进行转换非常困难。要精确的将屏幕坐标点转换为摄像头坐标点。开发者必须考虑诸如视频重力、镜像、图层变换和方向等因素进行综合计算。幸运的是，AVCaptureVideoPreviewLayer现在定义了一个转换方法让这一过程变得简单多了。
AVCaptureVideoPreviewLayer定义了2个方法用于坐标系间进行转换：
captureDevicePointOfInterestForPoint:获取屏幕坐标系的CGPoint 数据，返回转换得到的设备坐标系CGPoint数据。
pointForCaptureDevicePointOfInterest:获取摄像头坐标系的CGPoint数据，返回转换得到的屏幕坐标系CGPoint 数据。
THPreview View 使用captureDevicePointOfInterestForPoint:方法将用户触点信息转换为摄像头设备坐标系的中的点。在项目中点击对焦和点击曝光功能实现会用到这个转换坐标点。
总结
学习这篇文章重点，要弄明白预览视图的创建 和 坐标空间转换的方法。
链接：此链接下的项目已经搭建好UI。同学们，可以在这个基础上进行编码；
链接:http://pan.baidu.com/s/1c1A1NDA 密码:ca7o
行者常至，为者常成！