vo: move DR helper code to a separate source file

So it can be reused by vo_libmpv.c, which needs to use it in a slightly
different way.

1 files changed, 130 insertions, 0 deletions

diff --git a/video/out/dr_helper.c b/video/out/dr_helper.c
new file mode 100644
index 0000000000..e826d08dc4
--- /dev/null
+++ b/video/out/dr_helper.c
@@ -0,0 +1,130 @@
+#include <stdlib.h>
+#include <assert.h>
+#include <pthread.h>
+
+#include <libavutil/buffer.h>
+
+#include "mpv_talloc.h"
+#include "misc/dispatch.h"
+#include "osdep/atomic.h"
+#include "video/mp_image.h"
+
+#include "dr_helper.h"
+
+struct dr_helper {
+    pthread_t thread;
+    struct mp_dispatch_queue *dispatch;
+    atomic_ullong dr_in_flight;
+
+    struct mp_image *(*get_image)(void *ctx, int imgfmt, int w, int h,
+                                  int stride_align);
+    void *get_image_ctx;
+};
+
+static void dr_helper_destroy(void *ptr)
+{
+    struct dr_helper *dr = ptr;
+
+    // All references must have been freed on destruction, or we'll have
+    // dangling pointers.
+    assert(atomic_load(&dr->dr_in_flight) == 0);
+}
+
+struct dr_helper *dr_helper_create(struct mp_dispatch_queue *dispatch,
+            struct mp_image *(*get_image)(void *ctx, int imgfmt, int w, int h,
+                                          int stride_align),
+            void *get_image_ctx)
+{
+    struct dr_helper *dr = talloc_ptrtype(NULL, dr);
+    talloc_set_destructor(dr, dr_helper_destroy);
+    *dr = (struct dr_helper){
+        .thread = pthread_self(),
+        .dispatch = dispatch,
+        .dr_in_flight = ATOMIC_VAR_INIT(0),
+        .get_image = get_image,
+        .get_image_ctx = get_image_ctx,
+    };
+    return dr;
+}
+
+struct free_dr_context {
+    struct dr_helper *dr;
+    AVBufferRef *ref;
+};
+
+static void dr_thread_free(void *ptr)
+{
+    struct free_dr_context *ctx = ptr;
+
+    unsigned long long v = atomic_fetch_add(&ctx->dr->dr_in_flight, -1);
+    assert(v); // value before sub is 0 - unexpected underflow.
+
+    av_buffer_unref(&ctx->ref);
+    talloc_free(ctx);
+}
+
+static void free_dr_buffer_on_dr_thread(void *opaque, uint8_t *data)
+{
+    struct free_dr_context *ctx = opaque;
+
+    // The image could be unreffed even on the DR thread. In practice, this
+    // matters most on DR destruction.
+    if (pthread_equal(ctx->dr->thread, pthread_self())) {
+        dr_thread_free(ctx);
+    } else {
+        mp_dispatch_run(ctx->dr->dispatch, dr_thread_free, ctx);
+    }
+}
+
+struct get_image_cmd {
+    struct dr_helper *dr;
+    int imgfmt, w, h, stride_align;
+    struct mp_image *res;
+};
+
+static void sync_get_image(void *ptr)
+{
+    struct get_image_cmd *cmd = ptr;
+    struct dr_helper *dr = cmd->dr;
+
+    cmd->res = dr->get_image(dr->get_image_ctx, cmd->imgfmt, cmd->w, cmd->h,
+                             cmd->stride_align);
+    if (!cmd->res)
+        return;
+
+    // We require exactly 1 AVBufferRef.
+    assert(cmd->res->bufs[0]);
+    assert(!cmd->res->bufs[1]);
+
+    // Apply some magic to get it free'd on the DR thread as well. For this to
+    // work, we create a dummy-ref that aliases the original ref, which is why
+    // the original ref must be writable in the first place. (A newly allocated
+    // image should be always writable of course.)
+    assert(mp_image_is_writeable(cmd->res));
+
+    struct free_dr_context *ctx = talloc_zero(NULL, struct free_dr_context);
+    *ctx = (struct free_dr_context){
+        .dr = dr,
+        .ref = cmd->res->bufs[0],
+    };
+
+    AVBufferRef *new_ref = av_buffer_create(ctx->ref->data, ctx->ref->size,
+                                            free_dr_buffer_on_dr_thread, ctx, 0);
+    if (!new_ref)
+        abort(); // tiny malloc OOM
+
+    cmd->res->bufs[0] = new_ref;
+
+    atomic_fetch_add(&dr->dr_in_flight, 1);
+}
+
+struct mp_image *dr_helper_get_image(struct dr_helper *dr, int imgfmt,
+                                     int w, int h, int stride_align)
+{
+    struct get_image_cmd cmd = {
+        .dr = dr,
+        .imgfmt = imgfmt, .w = w, .h = h, .stride_align = stride_align,
+    };
+    mp_dispatch_run(dr->dispatch, sync_get_image, &cmd);
+    return cmd.res;
+}