Handle frame available from screen.c

As soon as the stream is started, the video buffer could notify a new
frame available.

In order to pass this event to the screen without race condition, the
screen must be initialized before the screen is started.

app/src/decoder.c

@@ -14,17 +14,7 @@
 // set the decoded frame as ready for rendering, and notify
 static void
 push_frame(struct decoder *decoder) {
-    bool previous_frame_skipped;
-    video_buffer_offer_decoded_frame(decoder->video_buffer,
-                                     &previous_frame_skipped);
-    if (previous_frame_skipped) {
-        // the previous EVENT_NEW_FRAME will consume this frame
-        return;
-    }
-    static SDL_Event new_frame_event = {
-        .type = EVENT_NEW_FRAME,
-    };
-    SDL_PushEvent(&new_frame_event);
+    video_buffer_producer_offer_frame(decoder->video_buffer);
 }
 
 void
@@ -66,7 +56,7 @@ decoder_push(struct decoder *decoder, const AVPacket *packet) {
         return false;
     }
     ret = avcodec_receive_frame(decoder->codec_ctx,
-                                decoder->video_buffer->decoding_frame);
+                                decoder->video_buffer->producer_frame);
     if (!ret) {
         // a frame was received
         push_frame(decoder);

app/src/fps_counter.c

@@ -168,7 +168,7 @@ fps_counter_add_rendered_frame(struct fps_counter *counter) {
 }
 
 void
-fps_counter_add_skipped_frame(struct fps_counter *counter) {
+fps_counter_add_skipped_frames(struct fps_counter *counter, unsigned n) {
     if (!is_started(counter)) {
         return;
     }
@@ -176,6 +176,6 @@ fps_counter_add_skipped_frame(struct fps_counter *counter) {
     sc_mutex_lock(&counter->mutex);
     uint32_t now = SDL_GetTicks();
     check_interval_expired(counter, now);
-    ++counter->nr_skipped;
+    counter->nr_skipped += n;
     sc_mutex_unlock(&counter->mutex);
 }

app/src/fps_counter.h

@@ -54,6 +54,6 @@ void
 fps_counter_add_rendered_frame(struct fps_counter *counter);
 
 void
-fps_counter_add_skipped_frame(struct fps_counter *counter);
+fps_counter_add_skipped_frames(struct fps_counter *counter, unsigned n);
 
 #endif

app/src/input_manager.c

@@ -480,9 +480,7 @@ input_manager_process_key(struct input_manager *im,
                 return;
             case SDLK_i:
                 if (!shift && !repeat && down) {
-                    struct fps_counter *fps_counter =
-                        im->video_buffer->fps_counter;
-                    switch_fps_counter_state(fps_counter);
+                    switch_fps_counter_state(im->fps_counter);
                 }
                 return;
             case SDLK_n:

app/src/input_manager.h

@@ -16,6 +16,7 @@
 struct input_manager {
     struct controller *controller;
     struct video_buffer *video_buffer;
+    struct fps_counter *fps_counter;
     struct screen *screen;
 
     // SDL reports repeated events as a boolean, but Android expects the actual

app/src/scrcpy.c

@@ -42,6 +42,7 @@ static struct file_handler file_handler;
 static struct input_manager input_manager = {
     .controller = &controller,
     .video_buffer = &video_buffer,
+    .fps_counter = &fps_counter,
     .screen = &screen,
     .repeat = 0,
 
@@ -266,6 +267,14 @@ av_log_callback(void *avcl, int level, const char *fmt, va_list vl) {
     free(local_fmt);
 }
 
+static void
+video_buffer_on_frame_available(struct video_buffer *vb, void *userdata) {
+    (void) vb;
+    (void) userdata;
+
+    screen_on_frame_available(&screen);
+}
+
 bool
 scrcpy(const struct scrcpy_options *options) {
     if (!server_init(&server)) {
@@ -332,8 +341,12 @@ scrcpy(const struct scrcpy_options *options) {
         }
         fps_counter_initialized = true;
 
-        if (!video_buffer_init(&video_buffer, &fps_counter,
-                               options->render_expired_frames)) {
+        static const struct video_buffer_callbacks video_buffer_cbs = {
+            .on_frame_available = video_buffer_on_frame_available,
+        };
+
+        if (!video_buffer_init(&video_buffer, options->render_expired_frames,
+                               &video_buffer_cbs, NULL)) {
             goto end;
         }
         video_buffer_initialized = true;
@@ -366,13 +379,6 @@ scrcpy(const struct scrcpy_options *options) {
 
     stream_init(&stream, server.video_socket, dec, rec);
 
-    // now we consumed the header values, the socket receives the video stream
-    // start the stream
-    if (!stream_start(&stream)) {
-        goto end;
-    }
-    stream_started = true;
-
     if (options->display) {
         if (options->control) {
             if (!controller_init(&controller, server.control_socket)) {
@@ -389,7 +395,7 @@ scrcpy(const struct scrcpy_options *options) {
         const char *window_title =
             options->window_title ? options->window_title : device_name;
 
-        screen_init(&screen, &video_buffer);
+        screen_init(&screen, &video_buffer, &fps_counter);
 
         if (!screen_init_rendering(&screen, window_title, frame_size,
                                    options->always_on_top, options->window_x,
@@ -415,6 +421,13 @@ scrcpy(const struct scrcpy_options *options) {
         }
     }
 
+    // now we consumed the header values, the socket receives the video stream
+    // start the stream
+    if (!stream_start(&stream)) {
+        goto end;
+    }
+    stream_started = true;
+
     input_manager_init(&input_manager, options);
 
     ret = event_loop(options);

app/src/screen.c

@@ -192,9 +192,11 @@ screen_update_content_rect(struct screen *screen) {
 }
 
 void
-screen_init(struct screen *screen, struct video_buffer *vb) {
+screen_init(struct screen *screen, struct video_buffer *vb,
+            struct fps_counter *fps_counter) {
     *screen = (struct screen) SCREEN_INITIALIZER;
     screen->vb = vb;
+    screen->fps_counter = fps_counter;
 }
 
 static inline SDL_Texture *
@@ -452,7 +454,13 @@ update_texture(struct screen *screen, const AVFrame *frame) {
 
 static bool
 screen_update_frame(struct screen *screen) {
-    const AVFrame *frame = video_buffer_take_rendering_frame(screen->vb);
+    unsigned skipped;
+    const AVFrame *frame =
+        video_buffer_consumer_take_frame(screen->vb, &skipped);
+
+    fps_counter_add_skipped_frames(screen->fps_counter, skipped);
+    fps_counter_add_rendered_frame(screen->fps_counter);
+
     struct size new_frame_size = {frame->width, frame->height};
     if (!prepare_for_frame(screen, new_frame_size)) {
         return false;
@@ -647,3 +655,15 @@ screen_hidpi_scale_coords(struct screen *screen, int32_t *x, int32_t *y) {
     *x = (int64_t) *x * dw / ww;
     *y = (int64_t) *y * dh / wh;
 }
+
+void
+screen_on_frame_available(struct screen *screen) {
+    (void) screen;
+
+    static SDL_Event new_frame_event = {
+        .type = EVENT_NEW_FRAME,
+    };
+
+    // Post the event on the UI thread
+    SDL_PushEvent(&new_frame_event);
+}

app/src/screen.h

@@ -14,6 +14,8 @@ struct video_buffer;
 
 struct screen {
     struct video_buffer *vb;
+    struct fps_counter *fps_counter;
+
     SDL_Window *window;
     SDL_Renderer *renderer;
     SDL_Texture *texture;
@@ -39,6 +41,7 @@ struct screen {
 
 #define SCREEN_INITIALIZER { \
     .vb = NULL, \
+    .fps_counter = NULL, \
     .window = NULL, \
     .renderer = NULL, \
     .texture = NULL, \
@@ -72,7 +75,8 @@ struct screen {
 
 // initialize default values
 void
-screen_init(struct screen *screen, struct video_buffer *vb);
+screen_init(struct screen *screen, struct video_buffer *vb,
+            struct fps_counter *fps_counter);
 
 // initialize screen, create window, renderer and texture (window is hidden)
 // window_x and window_y accept SC_WINDOW_POSITION_UNDEFINED
@@ -137,4 +141,9 @@ screen_convert_drawable_to_frame_coords(struct screen *screen,
 void
 screen_hidpi_scale_coords(struct screen *screen, int32_t *x, int32_t *y);
 
+// Notify the screen that a new frame is available in the video_buffer.
+// Called from a separate thread.
+void
+screen_on_frame_available(struct screen *screen);
+
 #endif

app/src/video_buffer.c

@@ -7,12 +7,11 @@
 #include "util/log.h"
 
 bool
-video_buffer_init(struct video_buffer *vb, struct fps_counter *fps_counter,
-                  bool render_expired_frames) {
-    vb->fps_counter = fps_counter;
-
-    vb->decoding_frame = av_frame_alloc();
-    if (!vb->decoding_frame) {
+video_buffer_init(struct video_buffer *vb, bool wait_consumer,
+                  const struct video_buffer_callbacks *cbs,
+                  void *cbs_userdata) {
+    vb->producer_frame = av_frame_alloc();
+    if (!vb->producer_frame) {
         goto error_0;
     }
 
@@ -21,8 +20,8 @@ video_buffer_init(struct video_buffer *vb, struct fps_counter *fps_counter,
         goto error_1;
     }
 
-    vb->rendering_frame = av_frame_alloc();
-    if (!vb->rendering_frame) {
+    vb->consumer_frame = av_frame_alloc();
+    if (!vb->consumer_frame) {
         goto error_2;
     }
 
@@ -31,8 +30,8 @@ video_buffer_init(struct video_buffer *vb, struct fps_counter *fps_counter,
         goto error_3;
     }
 
-    vb->render_expired_frames = render_expired_frames;
-    if (render_expired_frames) {
+    vb->wait_consumer = wait_consumer;
+    if (wait_consumer) {
         ok = sc_cond_init(&vb->pending_frame_consumed_cond);
         if (!ok) {
             sc_mutex_destroy(&vb->mutex);
@@ -47,89 +46,107 @@ video_buffer_init(struct video_buffer *vb, struct fps_counter *fps_counter,
     // consumed
     vb->pending_frame_consumed = true;
 
+    vb->skipped = 0;
+
+    assert(cbs);
+    assert(cbs->on_frame_available);
+    vb->cbs = cbs;
+    vb->cbs_userdata = cbs_userdata;
+
     return true;
 
 error_3:
-    av_frame_free(&vb->rendering_frame);
+    av_frame_free(&vb->consumer_frame);
 error_2:
     av_frame_free(&vb->pending_frame);
 error_1:
-    av_frame_free(&vb->decoding_frame);
+    av_frame_free(&vb->producer_frame);
 error_0:
     return false;
 }
 
 void
 video_buffer_destroy(struct video_buffer *vb) {
-    if (vb->render_expired_frames) {
+    if (vb->wait_consumer) {
         sc_cond_destroy(&vb->pending_frame_consumed_cond);
     }
     sc_mutex_destroy(&vb->mutex);
-    av_frame_free(&vb->rendering_frame);
+    av_frame_free(&vb->consumer_frame);
     av_frame_free(&vb->pending_frame);
-    av_frame_free(&vb->decoding_frame);
+    av_frame_free(&vb->producer_frame);
 }
 
 static void
-video_buffer_swap_decoding_frame(struct video_buffer *vb) {
+video_buffer_swap_producer_frame(struct video_buffer *vb) {
     sc_mutex_assert(&vb->mutex);
-    AVFrame *tmp = vb->decoding_frame;
-    vb->decoding_frame = vb->pending_frame;
+    AVFrame *tmp = vb->producer_frame;
+    vb->producer_frame = vb->pending_frame;
     vb->pending_frame = tmp;
 }
 
 static void
-video_buffer_swap_rendering_frame(struct video_buffer *vb) {
+video_buffer_swap_consumer_frame(struct video_buffer *vb) {
     sc_mutex_assert(&vb->mutex);
-    AVFrame *tmp = vb->rendering_frame;
-    vb->rendering_frame = vb->pending_frame;
+    AVFrame *tmp = vb->consumer_frame;
+    vb->consumer_frame = vb->pending_frame;
     vb->pending_frame = tmp;
 }
 
 void
-video_buffer_offer_decoded_frame(struct video_buffer *vb,
-                                 bool *previous_frame_skipped) {
+video_buffer_producer_offer_frame(struct video_buffer *vb) {
     sc_mutex_lock(&vb->mutex);
-    if (vb->render_expired_frames) {
+    if (vb->wait_consumer) {
         // wait for the current (expired) frame to be consumed
         while (!vb->pending_frame_consumed && !vb->interrupted) {
             sc_cond_wait(&vb->pending_frame_consumed_cond, &vb->mutex);
         }
-    } else if (!vb->pending_frame_consumed) {
-        fps_counter_add_skipped_frame(vb->fps_counter);
     }
 
-    video_buffer_swap_decoding_frame(vb);
+    video_buffer_swap_producer_frame(vb);
+
+    bool skipped = !vb->pending_frame_consumed;
+    if (skipped) {
+        ++vb->skipped;
+    }
 
-    *previous_frame_skipped = !vb->pending_frame_consumed;
     vb->pending_frame_consumed = false;
 
     sc_mutex_unlock(&vb->mutex);
+
+    if (!skipped) {
+        // If skipped, then the previous call will consume this frame, the
+        // callback must not be called
+        vb->cbs->on_frame_available(vb, vb->cbs_userdata);
+    }
 }
 
 const AVFrame *
-video_buffer_take_rendering_frame(struct video_buffer *vb) {
+video_buffer_consumer_take_frame(struct video_buffer *vb, unsigned *skipped) {
     sc_mutex_lock(&vb->mutex);
     assert(!vb->pending_frame_consumed);
     vb->pending_frame_consumed = true;
 
-    fps_counter_add_rendered_frame(vb->fps_counter);
+    video_buffer_swap_consumer_frame(vb);
 
-    video_buffer_swap_rendering_frame(vb);
-
-    if (vb->render_expired_frames) {
+    if (vb->wait_consumer) {
         // unblock video_buffer_offer_decoded_frame()
         sc_cond_signal(&vb->pending_frame_consumed_cond);
     }
+
+    if (skipped) {
+        *skipped = vb->skipped;
+    }
+    vb->skipped = 0; // reset
+
     sc_mutex_unlock(&vb->mutex);
 
-    // rendering_frame is only written from this thread, no need to lock
-    return vb->rendering_frame;
+    // consumer_frame is only written from this thread, no need to lock
+    return vb->consumer_frame;
 }
 
 void
 video_buffer_interrupt(struct video_buffer *vb) {
-    if (vb->render_expired_frames) {
+    if (vb->wait_consumer) {
         sc_mutex_lock(&vb->mutex);
         vb->interrupted = true;
         sc_mutex_unlock(&vb->mutex);

app/src/video_buffer.h

@@ -13,53 +13,62 @@ typedef struct AVFrame AVFrame;
 
 /**
  * There are 3 frames in memory:
- *  - one frame is held by the decoder (decoding_frame)
- *  - one frame is held by the renderer (rendering_frame)
- *  - one frame is shared between the decoder and the renderer (pending_frame)
+ *  - one frame is held by the producer (producer_frame)
+ *  - one frame is held by the consumer (consumer_frame)
+ *  - one frame is shared between the producer and the consumer (pending_frame)
  *
- * The decoder decodes a packet into the decoding_frame (it may takes time).
+ * The producer generates a frame into the producer_frame (it may takes time).
  *
- * Once the frame is decoded, it calls video_buffer_offer_decoded_frame(),
- * which swaps the decoding and pending frames.
+ * Once the frame is produced, it calls video_buffer_producer_offer_frame(),
+ * which swaps the producer and pending frames.
  *
- * When the renderer is notified that a new frame is available, it calls
- * video_buffer_take_rendering_frame() to retrieve it, which swaps the pending
- * and rendering frames. The frame is valid until the next call, without
- * blocking the decoder.
+ * When the consumer is notified that a new frame is available, it calls
+ * video_buffer_consumer_take_frame() to retrieve it, which swaps the pending
+ * and consumer frames. The frame is valid until the next call, without
+ * blocking the producer.
  */
 
 struct video_buffer {
-    AVFrame *decoding_frame;
+    AVFrame *producer_frame;
     AVFrame *pending_frame;
-    AVFrame *rendering_frame;
+    AVFrame *consumer_frame;
 
     sc_mutex mutex;
-    bool render_expired_frames;
+    bool wait_consumer; // never overwrite a pending frame if it is not consumed
     bool interrupted;
 
     sc_cond pending_frame_consumed_cond;
     bool pending_frame_consumed;
 
-    struct fps_counter *fps_counter;
+    unsigned skipped;
+
+    const struct video_buffer_callbacks *cbs;
+    void *cbs_userdata;
+};
+
+struct video_buffer_callbacks {
+    // Called when a new frame can be consumed by
+    // video_buffer_consumer_take_frame(vb)
+    void (*on_frame_available)(struct video_buffer *vb, void *userdata);
 };
 
 bool
-video_buffer_init(struct video_buffer *vb, struct fps_counter *fps_counter,
-                  bool render_expired_frames);
+video_buffer_init(struct video_buffer *vb, bool wait_consumer,
+                  const struct video_buffer_callbacks *cbs, void *cbs_userdata);
 
 void
 video_buffer_destroy(struct video_buffer *vb);
 
-// set the decoded frame as ready for rendering
-// the output flag is set to report whether the previous frame has been skipped
+// set the producer frame as ready for consuming
 void
-video_buffer_offer_decoded_frame(struct video_buffer *vb,
-                                 bool *previous_frame_skipped);
+video_buffer_producer_offer_frame(struct video_buffer *vb);
 
-// mark the rendering frame as consumed and return it
+// mark the consumer frame as consumed and return it
 // the frame is valid until the next call to this function
+// the output parameter "skipped" indicates how many produced frames have been
+// skipped
 const AVFrame *
-video_buffer_take_rendering_frame(struct video_buffer *vb);
+video_buffer_consumer_take_frame(struct video_buffer *vb, unsigned *skipped);
 
 // wake up and avoid any blocking call
 void