iPhone 使用 AVCaptureVideoPreviewLayer 拍摄增强现实屏幕截图

Question

我有一个正在开发的小型增强现实应用程序，我想知道如何保存用户通过点击按钮或计时器看到的内容的屏幕截图。

该应用通过在另一个 UIView 上方叠加实时摄像头画面来工作。我可以使用电源按钮 + 主页按钮保存屏幕截图，这些将保存到相机胶卷中。但是，即使我要求窗口自行保存，Apple 也不会渲染 AVCaptureVideoPreviewLayer。它将在预览层所在的位置创建一 block 透明的 Canvas 。

增强现实应用保存屏幕截图(包括透明度和 subview )的正确方法是什么？

//displaying a live preview on one of the views
    -(void)startCapture
{
        captureSession = [[AVCaptureSession alloc] init];
        AVCaptureDevice *audioCaptureDevice = nil;

        //           AVCaptureDevice *audioCaptureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

        NSArray *videoDevices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];

        for (AVCaptureDevice *device in videoDevices) {

            if(useFrontCamera){
                if (device.position == AVCaptureDevicePositionFront) {
                    //FRONT-FACING CAMERA EXISTS
                    audioCaptureDevice = device;
                    break;
                }
            }else{
                if (device.position == AVCaptureDevicePositionBack) {
                    //Rear-FACING CAMERA EXISTS
                    audioCaptureDevice = device;
                    break;
                }
            }

        }


        NSError *error = nil;
        AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioCaptureDevice error:&error];
        if (audioInput) {
            [captureSession addInput:audioInput];
        }
        else {
            // Handle the failure.
        }


if([captureSession canAddOutput:captureOutput]){
 captureOutput = [[AVCaptureVideoDataOutput alloc] init];
    [captureOutput setAlwaysDiscardsLateVideoFrames:YES];
    [captureOutput setSampleBufferDelegate:self queue:queue];
    [captureOutput setVideoSettings:videoSettings];

    dispatch_release(queue);
}else{
//handle failure
}

        previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:captureSession];
        UIView *aView = arOverlayView;
        previewLayer.frame =CGRectMake(0,0, arOverlayView.frame.size.width,arOverlayView.frame.size.height); // Assume you want the preview layer to fill the view.

        [aView.layer addSublayer:previewLayer];
        [captureSession startRunning];


}

//ask the entire window to draw itself in a graphics context. This call will not render

//AVCaptureVideoPreviewLayer .它必须替换为 UIImageView 或基于 GL 的 View 。//请参阅以下代码以创建动态更新的 UIImageView -(void)saveScreenshot {

   UIGraphicsBeginImageContext(appDelegate.window.bounds.size);

    [appDelegate.window.layer renderInContext:UIGraphicsGetCurrentContext()];

    UIImage *screenshot = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIImageWriteToSavedPhotosAlbum(screenshot, self, 
                                   @selector(image:didFinishSavingWithError:contextInfo:), nil);


}


//image saved to camera roll callback
- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error 
  contextInfo:(void *)contextInfo
{
    // Was there an error?
    if (error != NULL)
    {
        // Show error message...
         NSLog(@"save failed");

    }
    else  // No errors
    {
         NSLog(@"save successful");
        // Show message image successfully saved
    }
}

这是创建图像的代码:

//您需要将您的 View Controller 作为委托(delegate)添加到相机输出以接收缓冲数据通知

-(void)activateCameraFeed
{
//this is the code responsible for capturing feed for still image processing
 dispatch_queue_t queue = dispatch_queue_create("com.AugmentedRealityGlamour.ImageCaptureQueue", NULL);

    captureOutput = [[AVCaptureVideoDataOutput alloc] init];
    [captureOutput setAlwaysDiscardsLateVideoFrames:YES];
    [captureOutput setSampleBufferDelegate:self queue:queue];
    [captureOutput setVideoSettings:videoSettings];

    dispatch_release(queue);

//......configure audio feed, add inputs and outputs

}

//buffer delegate callback
- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
    if ( ignoreImageStream )
        return;
       [self performImageCaptureFrom:sampleBuffer];

} 

创建一个 UIImage:

- (void) performImageCaptureFrom:(CMSampleBufferRef)sampleBuffer
{
    CVImageBufferRef imageBuffer;

    if ( CMSampleBufferGetNumSamples(sampleBuffer) != 1 )
        return;
    if ( !CMSampleBufferIsValid(sampleBuffer) )
        return;
    if ( !CMSampleBufferDataIsReady(sampleBuffer) )
        return;

    imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 

    if ( CVPixelBufferGetPixelFormatType(imageBuffer) != kCVPixelFormatType_32BGRA )
        return;

    CVPixelBufferLockBaseAddress(imageBuffer,0); 

    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer); 

    CGImageRef newImage = nil;

    if ( cameraDeviceSetting == CameraDeviceSetting640x480 )
    {
        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
        CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
        newImage = CGBitmapContextCreateImage(newContext);
        CGColorSpaceRelease( colorSpace );
        CGContextRelease(newContext);
    }
    else
    {
        uint8_t *tempAddress = malloc( 640 * 4 * 480 );
        memcpy( tempAddress, baseAddress, bytesPerRow * height );
        baseAddress = tempAddress;
        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
        CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace,  kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipFirst);
        newImage = CGBitmapContextCreateImage(newContext);
        CGContextRelease(newContext);
        newContext = CGBitmapContextCreate(baseAddress, 640, 480, 8, 640*4, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
        CGContextScaleCTM( newContext, (CGFloat)640/(CGFloat)width, (CGFloat)480/(CGFloat)height );
        CGContextDrawImage(newContext, CGRectMake(0,0,640,480), newImage);
        CGImageRelease(newImage);
        newImage = CGBitmapContextCreateImage(newContext);
        CGColorSpaceRelease( colorSpace );
        CGContextRelease(newContext);
        free( tempAddress );
    }

    if ( newImage != nil )
    {

//modified for iOS5.0 with ARC    
    tempImage =  [[UIImage alloc] initWithCGImage:newImage scale:(CGFloat)1.0 orientation:cameraImageOrientation];
    CGImageRelease(newImage);

//this call creates the illusion of a preview layer, while we are actively switching images created with this method
        [self performSelectorOnMainThread:@selector(newCameraImageNotification:) withObject:tempImage waitUntilDone:YES];
    }

    CVPixelBufferUnlockBaseAddress(imageBuffer,0);
}

用实际上可以在图形上下文中呈现的 UIView 更新界面:

- (void) newCameraImageNotification:(UIImage*)newImage
{
    if ( newImage == nil )
        return;

        [arOverlayView setImage:newImage];
//or do more advanced processing of the image
}

Answer 1

如果您想要屏幕上的快照，这就是我在我的一个相机应用程序中所做的。我已经很长时间没有碰过这段代码了，所以现在可能有更好的 5.0 方式，但它已经超过 100 万次下载。有一个用于抓取基于 UIView 的屏幕的函数和一个用于抓取 Open/GLES1 屏幕的函数:

//
//  ScreenCapture.m
//  LiveEffectsCam
//
//  Created by John Carter on 10/8/10.
//

#import "ScreenCapture.h"

#import <QuartzCore/CABase.h>
#import <QuartzCore/CATransform3D.h>
#import <QuartzCore/CALayer.h>
#import <QuartzCore/CAScrollLayer.h>

#import <OpenGLES/EAGL.h>
#import <OpenGLES/ES1/gl.h>
#import <OpenGLES/ES1/glext.h>
#import <QuartzCore/QuartzCore.h>
#import <OpenGLES/EAGLDrawable.h>


@implementation ScreenCapture

+ (UIImage *) GLViewToImage:(GLView *)glView
{
    UIImage *glImage = [GLView snapshot:glView]; // returns an autoreleased image
    return glImage;
}

+ (UIImage *) GLViewToImage:(GLView *)glView withOverlayImage:(UIImage *)overlayImage
{
    UIImage *glImage = [GLView snapshot:glView]; // returns an autoreleased image

    // Merge Image and Overlay
    //
    CGRect imageRect = CGRectMake((CGFloat)0.0, (CGFloat)0.0, glImage.size.width*glImage.scale, glImage.size.height*glImage.scale);
    CGImageRef overlayCopy = CGImageCreateCopy( overlayImage.CGImage );
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL, (int)glImage.size.width*glImage.scale, (int)glImage.size.height*glImage.scale, 8, (int)glImage.size.width*4*glImage.scale, colorSpace, kCGImageAlphaPremultipliedLast);
    CGContextDrawImage(context, imageRect, glImage.CGImage);
    CGContextDrawImage(context, imageRect, overlayCopy);
    CGImageRef newImage = CGBitmapContextCreateImage(context);
    UIImage *combinedViewImage = [[[UIImage alloc] initWithCGImage:newImage] autorelease];
    CGImageRelease(newImage);
    CGImageRelease(overlayCopy);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    return combinedViewImage;
}

+ (UIImage *) UIViewToImage:(UIView *)view withOverlayImage:(UIImage *)overlayImage
    {
    UIImage *viewImage = [ScreenCapture UIViewToImage:view]; // returns an autoreleased image

    // Merge Image and Overlay
    //
    CGRect imageRect = CGRectMake((CGFloat)0.0, (CGFloat)0.0, viewImage.size.width*viewImage.scale, viewImage.size.height*viewImage.scale);
    CGImageRef overlayCopy = CGImageCreateCopy( overlayImage.CGImage );
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL, (int)viewImage.size.width*viewImage.scale, (int)viewImage.size.height*viewImage.scale, 8, (int)viewImage.size.width*4*viewImage.scale, colorSpace, kCGImageAlphaPremultipliedLast);
    CGContextDrawImage(context, imageRect, viewImage.CGImage);
    CGContextDrawImage(context, imageRect, overlayCopy);
    CGImageRef newImage = CGBitmapContextCreateImage(context);
    UIImage *combinedViewImage = [[[UIImage alloc] initWithCGImage:newImage] autorelease];
    CGImageRelease(newImage);
    CGImageRelease(overlayCopy);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    return combinedViewImage;
}



+ (UIImage *) UIViewToImage:(UIView *)view
{
    // Create a graphics context with the target size
    // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
    // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
    //
    // CGSize imageSize = [[UIScreen mainScreen] bounds].size;
    CGSize imageSize = CGSizeMake( (CGFloat)480.0, (CGFloat)640.0 );        // camera image size

    if (NULL != UIGraphicsBeginImageContextWithOptions)
        UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
    else
        UIGraphicsBeginImageContext(imageSize);

    CGContextRef context = UIGraphicsGetCurrentContext();

    // Start with the view...
    //
    CGContextSaveGState(context);
    CGContextTranslateCTM(context, [view center].x, [view center].y);
    CGContextConcatCTM(context, [view transform]);
    CGContextTranslateCTM(context,-[view bounds].size.width * [[view layer] anchorPoint].x,-[view bounds].size.height * [[view layer] anchorPoint].y);
    [[view layer] renderInContext:context];
    CGContextRestoreGState(context);

    // ...then repeat for every subview from back to front
    //
    for (UIView *subView in [view subviews]) 
    {
        if ( [subView respondsToSelector:@selector(screen)] )
            if ( [(UIWindow *)subView screen] == [UIScreen mainScreen] )
                continue;

        CGContextSaveGState(context);
        CGContextTranslateCTM(context, [subView center].x, [subView center].y);
        CGContextConcatCTM(context, [subView transform]);
        CGContextTranslateCTM(context,-[subView bounds].size.width * [[subView layer] anchorPoint].x,-[subView bounds].size.height * [[subView layer] anchorPoint].y);
        [[subView layer] renderInContext:context];
        CGContextRestoreGState(context);
    }

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();   // autoreleased image

    UIGraphicsEndImageContext();

    return image;
}

+ (UIImage *) snapshot:(GLView *)eaglview
{
    NSInteger x = 0;
    NSInteger y = 0;
    NSInteger width = [eaglview backingWidth];
    NSInteger height = [eaglview backingHeight];
    NSInteger dataLength = width * height * 4;

    NSUInteger i;
    for ( i=0; i<100; i++ )
    {
        glFlush();
        CFRunLoopRunInMode(kCFRunLoopDefaultMode, (float)1.0/(float)60.0, FALSE);
    }

    GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));

    // Read pixel data from the framebuffer
    //
    glPixelStorei(GL_PACK_ALIGNMENT, 4);
    glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data);

    // Create a CGImage with the pixel data
    // If your OpenGL ES content is opaque, use kCGImageAlphaNoneSkipLast to ignore the alpha channel
    // otherwise, use kCGImageAlphaPremultipliedLast
    //
    CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, data, dataLength, NULL);
    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
    CGImageRef iref = CGImageCreate(width, height, 8, 32, width * 4, colorspace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast, ref, NULL, true, kCGRenderingIntentDefault);

    // OpenGL ES measures data in PIXELS
    // Create a graphics context with the target size measured in POINTS
    //
    NSInteger widthInPoints;
    NSInteger heightInPoints;

    if (NULL != UIGraphicsBeginImageContextWithOptions)
    {
        // On iOS 4 and later, use UIGraphicsBeginImageContextWithOptions to take the scale into consideration
        // Set the scale parameter to your OpenGL ES view's contentScaleFactor
        // so that you get a high-resolution snapshot when its value is greater than 1.0
        //
        CGFloat scale = eaglview.contentScaleFactor;
        widthInPoints = width / scale;
        heightInPoints = height / scale;
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(widthInPoints, heightInPoints), NO, scale);
    }
    else
    {
        // On iOS prior to 4, fall back to use UIGraphicsBeginImageContext
        //
        widthInPoints = width;
        heightInPoints = height;
        UIGraphicsBeginImageContext(CGSizeMake(widthInPoints, heightInPoints));
    }

    CGContextRef cgcontext = UIGraphicsGetCurrentContext();

    // UIKit coordinate system is upside down to GL/Quartz coordinate system
    // Flip the CGImage by rendering it to the flipped bitmap context
    // The size of the destination area is measured in POINTS
    //
    CGContextSetBlendMode(cgcontext, kCGBlendModeCopy);
    CGContextDrawImage(cgcontext, CGRectMake(0.0, 0.0, widthInPoints, heightInPoints), iref);

    // Retrieve the UIImage from the current context
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();   // autoreleased image

    UIGraphicsEndImageContext();

    // Clean up
    free(data);
    CFRelease(ref);
    CFRelease(colorspace);
    CGImageRelease(iref);

    return image;
}

@end