Multi-threaded frame calculation for movie clip proxies

This commit implements multi-threaded calculation of frames
when building proxies. Both scaling and undistortion steps
are now threaded.

Frames and proxy resolution are still handled one-by-one,
saving files after every single step. So if HDD is not so
fast, this commit could have not so much benefit.

Internal changes:

- Added IMB_scaleImBuf_threaded which scales given image
  buffer in multiple threads and uses bilinear filtering.

- libmv's camera intrinsics now have SetThreads() method
  which is used to specify how many OpenMP threads to use
  for buffer distortion/undistortion.

  And yeah, this code is using OpenMP for threading.

- Reshuffled a bit libmv-capi calls and added function
  BKE_tracking_distortion_set_threads to specify number
  of threads used by intrinscis.

1 files changed, 4 insertions, 0 deletions

diff --git a/extern/libmv/libmv-capi.h b/extern/libmv/libmv-capi.h
index c90322c56c5..c3debe45fd1 100644
--- a/extern/libmv/libmv-capi.h
+++ b/extern/libmv/libmv-capi.h
@@ -132,6 +132,8 @@ void libmv_destroyFeatures(struct libmv_Features *libmv_features);
 /* camera intrinsics */
 struct libmv_CameraIntrinsics *libmv_ReconstructionExtractIntrinsics(struct libmv_Reconstruction *libmv_Reconstruction);
 
+struct libmv_CameraIntrinsics *libmv_CameraIntrinsicsNewEmpty(void);
+
 struct libmv_CameraIntrinsics *libmv_CameraIntrinsicsNew(libmv_cameraIntrinsicsOptions *libmv_camera_intrinsics_options);
 
 struct libmv_CameraIntrinsics *libmv_CameraIntrinsicsCopy(struct libmv_CameraIntrinsics *libmv_intrinsics);
@@ -141,6 +143,8 @@ void libmv_CameraIntrinsicsDestroy(struct libmv_CameraIntrinsics *libmv_intrinsi
 void libmv_CameraIntrinsicsUpdate(struct libmv_CameraIntrinsics *libmv_intrinsics,
                                   libmv_cameraIntrinsicsOptions *libmv_camera_intrinsics_options);
 
+void libmv_CameraIntrinsicsSetThreads(struct libmv_CameraIntrinsics *libmv_intrinsics, int threads);
+
 void libmv_CameraIntrinsicsExtract(struct libmv_CameraIntrinsics *libmv_intrinsics, double *focal_length,
 			double *principal_x, double *principal_y, double *k1, double *k2, double *k3, int *width, int *height);