Cocoa class for capturing the web cam and building an image up by rows of pixels

CaptureViewController.m

//
//  CaptureViewController.m
//  TimeSmear
//
//  Created by Lee Probert on 23/02/2012.
//  Copyright (c) 2012 LyraSpace Ltd. All rights reserved.
//

#import "CaptureViewController.h"

@implementation CaptureViewController

@synthesize captureButton, imageView, captureView, captureSession, captureDeviceInput, captureDeviceOutput;

-(IBAction)captureButtonHandler:(id)sender
{
    NSLog(@"capture button pressed");
    
    ypos = 0;
    isSmearing = YES;
    
    if(!captureSession)
    {
        captureSession = [[QTCaptureSession alloc] init];
        
        QTCaptureDevice *videoDevice = [QTCaptureDevice defaultInputDeviceWithMediaType:QTMediaTypeVideo];
        
        BOOL success = NO;
        
        NSError *error;
        
        success = [videoDevice open:&error];
        
        if (!success) {
            [[NSAlert alertWithError:error] runModal];
            return;
        }
        
        captureDeviceInput = [[QTCaptureDeviceInput alloc] initWithDevice:videoDevice];
        
        [captureSession addInput:captureDeviceInput error:nil];
        
        
        // Add a decompressed video output that returns raw frames to the session
        captureDeviceOutput = [[QTCaptureDecompressedVideoOutput alloc] init];
        [captureDeviceOutput setDelegate:self];
        
        success = [captureSession addOutput:captureDeviceOutput error:&error];
        
        if (!success) {
            [[NSAlert alertWithError:error] runModal];
            return;
        }
        
        [captureView setCaptureSession:captureSession];
        
        [captureSession startRunning];
    }
}

//---------------------------------------------------------

- (void)captureOutput:(QTCaptureOutput *)captureOutput didOutputVideoFrame:(CVImageBufferRef)videoFrame withSampleBuffer:(QTSampleBuffer *)sampleBuffer fromConnection:(QTCaptureConnection *)connection
{
    // Store the latest frame
	// This must be done in a @synchronized block because this delegate method is not called on the main thread
    
    CVImageBufferRef imageBufferRef;
    
    @synchronized (self) 
    {
        imageBufferRef = videoFrame;
    }
    
    if(imageBufferRef && isSmearing)
    {
        NSCIImageRep *imageRep = [NSCIImageRep imageRepWithCIImage:[CIImage imageWithCVImageBuffer:imageBufferRef]];
        
        if(!compositeImage) compositeImage = [[NSImage alloc] initWithSize:[imageRep size]];
        
        NSImage *videoFrameImage = [[NSImage alloc] initWithSize:[imageRep size]];
        
        [videoFrameImage addRepresentation:imageRep];
        
        NSRect r = NSMakeRect(0.0f, ypos, [imageRep size].width, 1);
        
        [compositeImage lockFocus];
        
        [videoFrameImage drawAtPoint:NSMakePoint(0.0f, ypos) fromRect:r operation:NSCompositeSourceOver fraction:1.0f];
        
        [compositeImage unlockFocus];
        
        [imageView setImage:compositeImage];
        
        ypos++;
        
        [[self view] setNeedsDisplay:YES];
        
        if(ypos >= [imageRep size].height)
        {
            isSmearing = NO;
            [captureSession stopRunning];
        }
    }
}

@end