hwcontext: Improve allocation in derived contexts

Use the flags argument of av_hwframe_ctx_create_derived() to pass the
mapping flags which will be used on allocation.  Also, set the format
and hardware context on the allocated frame automatically - the user
should not be required to do this themselves.

(cherry picked from commit c5714b51)

doc/APIchanges

@@ -15,6 +15,10 @@ libavutil:     2015-08-28
 
 API changes, most recent first:
 
+2017-06-14 - xxxxxxx - lavu 55.66.100 - hwcontext.h
+  av_hwframe_ctx_create_derived() now takes some AV_HWFRAME_MAP_* combination
+  as its flags argument (which was previously unused).
+
 2017-06-14 - xxxxxxx - lavc 57.99.100 - avcodec.h
   Add AV_HWACCEL_FLAG_ALLOW_PROFILE_MISMATCH.
 

libavutil/hwcontext.c

@@ -458,6 +458,11 @@ int av_hwframe_get_buffer(AVBufferRef *hwframe_ref, AVFrame *frame, int flags)
         // and map the frame immediately.
         AVFrame *src_frame;
 
+        frame->format = ctx->format;
+        frame->hw_frames_ctx = av_buffer_ref(hwframe_ref);
+        if (!frame->hw_frames_ctx)
+            return AVERROR(ENOMEM);
+
         src_frame = av_frame_alloc();
         if (!src_frame)
             return AVERROR(ENOMEM);
@@ -467,7 +472,8 @@ int av_hwframe_get_buffer(AVBufferRef *hwframe_ref, AVFrame *frame, int flags)
         if (ret < 0)
             return ret;
 
-        ret = av_hwframe_map(frame, src_frame, 0);
+        ret = av_hwframe_map(frame, src_frame,
+                             ctx->internal->source_allocation_map_flags);
         if (ret) {
             av_log(ctx, AV_LOG_ERROR, "Failed to map frame into derived "
                    "frame context: %d.\n", ret);
@@ -819,6 +825,12 @@ int av_hwframe_ctx_create_derived(AVBufferRef **derived_frame_ctx,
         goto fail;
     }
 
+    dst->internal->source_allocation_map_flags =
+        flags & (AV_HWFRAME_MAP_READ      |
+                 AV_HWFRAME_MAP_WRITE     |
+                 AV_HWFRAME_MAP_OVERWRITE |
+                 AV_HWFRAME_MAP_DIRECT);
+
     ret = AVERROR(ENOSYS);
     if (src->internal->hw_type->frames_derive_from)
         ret = src->internal->hw_type->frames_derive_from(dst, src, flags);

libavutil/hwcontext.h

@@ -566,7 +566,9 @@ int av_hwframe_map(AVFrame *dst, const AVFrame *src, int flags);
  *                           AVHWFramesContext on.
  * @param source_frame_ctx   A reference to an existing AVHWFramesContext
  *                           which will be mapped to the derived context.
- * @param flags  Currently unused; should be set to zero.
+ * @param flags  Some combination of AV_HWFRAME_MAP_* flags, defining the
+ *               mapping parameters to apply to frames which are allocated
+ *               in the derived device.
  * @return       Zero on success, negative AVERROR code on failure.
  */
 int av_hwframe_ctx_create_derived(AVBufferRef **derived_frame_ctx,

libavutil/hwcontext_internal.h

@@ -121,6 +121,11 @@ struct AVHWFramesInternal {
      * context it was derived from.
      */
     AVBufferRef *source_frames;
+    /**
+     * Flags to apply to the mapping from the source to the derived
+     * frame context when trying to allocate in the derived context.
+     */
+    int source_allocation_map_flags;
 };
 
 typedef struct HWMapDescriptor {

libavutil/version.h

@@ -80,7 +80,7 @@
 
 
 #define LIBAVUTIL_VERSION_MAJOR  55
-#define LIBAVUTIL_VERSION_MINOR  65
+#define LIBAVUTIL_VERSION_MINOR  66
 #define LIBAVUTIL_VERSION_MICRO 100
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \