Images Example

The Ultraleap Tracking Service creates the tracking data provided in a LEAP_TRACKING_EVENT() struct by analyzing a set of stereo images taken by the Ultraleap Hand Tracking Camera.

You can subscribe to receive the images LeapC is analyzing by setting the eLeapPolicyFlag_Images policy flag. This will cause LeapC to start dispatching LEAP_IMAGE_EVENT messages through the usual message pump.

Unsubscribing is achieved by calling LeapSetPolicyFlags again with eLeapPolicyFlag_Images as the “clear” argument.

ImageSample.c

The ImageSample.c program uses the callback mechanism defined by the ExampleConnection described in the other examples. Instead of printing out frame information, though, ImageSample keeps track of the latest images that the LeapC API has provided.

LeapC allocates the memory for the images that it provides, and will not release the memory for a set of images until:

• The client has polled and received the LEAP_IMAGE_EVENT containing that image’s data

• The client has polled and received the next LEAP_IMAGE_EVENT

If the client wants access to the image after this point then they should copy the data into another, user-allocated, buffer.

The buffer size needed for a set of images is determined by the image dimensions, the image bytes-per-pixel, and the number of images in the set. Each image’s dimensions are contained in the LEAP_IMAGE_PROPERTIES structure. For a typical image from a Leap Motion Controller, this size is:

640 (width) * 240 (height) * 1 (byte-per-pixel) * 2 (images) = 307200 bytes

The full sample code is:

#include <stdio.h>
#include <stdlib.h>
#include "LeapC.h"
#include "ExampleConnection.h"

/** Callback for when the connection opens. */
static void OnConnect(void){
  printf("Connected.\n");
}

/** Callback for when a device is found. */
static void OnDevice(const LEAP_DEVICE_INFO *props){
  printf("Found device %s.\n", props->serial);
}

/** Callback for when a frame of tracking data is available. */
static void OnFrame(const LEAP_TRACKING_EVENT *frame){
  printf("Frame %lli with %i hands.\n", (long long int)frame->info.frame_id, frame->nHands);
  for(uint32_t h = 0; h < frame->nHands; h++){
    LEAP_HAND* hand = &frame->pHands[h];
    printf("    Hand id %i is a %s hand with position (%f, %f, %f).\n",
                hand->id,
                (hand->type == eLeapHandType_Left ? "left" : "right"),
                hand->palm.position.x,
                hand->palm.position.y,
                hand->palm.position.z);
  }
}

/** Callback for when an image is available. */
static void OnImage(const LEAP_IMAGE_EVENT *imageEvent){
    printf("Received image set for frame %lli with size %lli.\n",
           (long long int)imageEvent->info.frame_id,
           (long long int)imageEvent->image[0].properties.width*
           (long long int)imageEvent->image[0].properties.height*2);
}

int main(int argc, char** argv) {
  //Set callback function pointers
  ConnectionCallbacks.on_connection          = &OnConnect;
  ConnectionCallbacks.on_device_found        = &OnDevice;
  ConnectionCallbacks.on_frame               = &OnFrame;
  ConnectionCallbacks.on_image               = &OnImage;

  LEAP_CONNECTION *connection = OpenConnection();
  LeapSetPolicyFlags(*connection, eLeapPolicyFlag_Images, 0);

  printf("Press Enter to exit program.\n");
  getchar();
  CloseConnection();
  DestroyConnection();
  return 0;
}
//End-of-Sample

Note that this example does not attempt to display image data graphically.

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