Working out how to use libfreenect in Objective-C

I’ve finally got round to starting it… working out how to use this libfreenect thing in my project. So, I’ve downloaded the libfreenect files and I’ve started looking at the .c example. It creates a window using OpenGL and displays basic Kinect data in it (RGB view and IR view).

My task now is to work out how to use it in my project. Firstly, work out how to use it in C and then see if I can also use it in Objective-C.

… lots of reverse engineering of code…

… a while later…

DONE! -ish. I have managed to reverse engineer the example program to a point where I can get my own program to find the number of Kinect devices connected, connect to the device, change the tilt and LED colour of the device and then disconnect from the device.

I have managed to recreate it in C and then I realised that it would be even easier to make it work in Objective-C! Well kinda easier for me because I’ve been using Objective-C so much recently..

So, here is my C version of the program (the main.c file) which carries out basic movement every time it connects successfully.

#include "libfreenect.h"
#include <stdio.h>

freenect_context *freenectContext;
freenect_device *freenectDevice;
int noDevicesConnected;
int error;

int main(int argc, char **argv) {
    // freenect_init initialises a freenect context. The second parameter can be NULL if not using mutliple contexts.
    // freenect_set_log_level sets the log level for the specified freenect context.
    // freenect_select_subdevices selects which subdevices to open when connecting to a new kinect device.
    freenect_init(&freenectContext, NULL);
    freenect_set_log_level(freenectContext, FREENECT_LOG_DEBUG);
    freenect_select_subdevices(freenectContext, (freenect_device_flags)(FREENECT_DEVICE_MOTOR | FREENECT_DEVICE_CAMERA));

    noDevicesConnected = freenect_num_devices(freenectContext);
    printf("Number of devices connected: %d\n", noDevicesConnected);
    // Exit the app if there are no devices connected.
    if (noDevicesConnected < 1) return 1;

    // freenect_open_device opens a Kinect device.
    error = freenect_open_device(freenectContext, &freenectDevice, 0);
    if (error < 0) {
        // Then exit the app if there was an error while connecting.
        printf("Could not open the Kinect device.");
        return 1;
    }

    freenect_set_tilt_degs(freenectDevice, 30);
    freenect_set_led(freenectDevice, LED_BLINK_RED_YELLOW);
    printf("Done Functions\n");

    freenect_close_device(freenectDevice);
    freenect_shutdown(freenectContext);
    printf("Done!\n");

    return 0;
}

And now theres my Objective-C program which gives you a GUI and allows you to manually control the tilt of the Kinect using a slider control. Here is the interface file:

#import <Foundation/Foundation.h>
#import "libfreenect.h"

@interface KinectMotorController : NSObject {
    freenect_context *kinectContext;
    freenect_device *kinectDevice;

    NSNumber *noDevicesConnected;
    NSInteger error;
}
@property (assign) IBOutlet NSTextField *numberOfDevices;
@property (assign) IBOutlet NSTextField *connectedBool;
@property (assign) IBOutlet NSSlider *tiltControl;

- (IBAction)findDevices:(id)sender;
- (IBAction)connectDevices:(id)sender;
- (IBAction)changeTilt:(id)sender;
- (IBAction)disconnectDevices:(id)sender;

@end

And now the implementation file:

#import "KinectMotorController.h"

@implementation KinectMotorController
@synthesize numberOfDevices;
@synthesize connectedBool;
@synthesize tiltControl;

- (IBAction)findDevices:(id)sender {
	// Initialise the freenect library.
	freenect_init(&kinectContext, NULL);
	freenect_set_log_level(kinectContext, FREENECT_LOG_DEBUG);
	freenect_select_subdevices(kinectContext, (freenect_device_flags)(FREENECT_DEVICE_MOTOR | FREENECT_DEVICE_CAMERA));

	// Find the devices collected and show the user the number.
	noDevicesConnected = [NSNumber numberWithInt:freenect_num_devices(kinectContext)];
	[numberOfDevices setStringValue:[noDevicesConnected stringValue]];
}

- (IBAction)connectDevices:(id)sender {
	error = freenect_open_device(kinectContext, &kinectDevice, 0);
	if (error < 0) {
		[connectedBool setStringValue:@"Failed to connect!"];
	} else {
		freenect_set_led(kinectDevice, LED_GREEN);
		[connectedBool setStringValue:@"Connected!"];
	}
}

- (IBAction)changeTilt:(id)sender {
	freenect_set_tilt_degs(kinectDevice, [tiltControl intValue]);
}

- (IBAction)disconnectDevices:(id)sender {
	freenect_set_led(kinectDevice, LED_RED);
	freenect_close_device(kinectDevice);
	freenect_shutdown(kinectContext);
	[connectedBool setStringValue:@"Disconnected."];
}
@end

So there we are 🙂 That really wasn’t as bad as I thought it would be. When I first saw the libfreenect code it looked like a bit of nightmare but at the moment its fine. We will see what happens when I try to start getting the camera data though… It might turn out to be a bit mental.