From ba20aec53960f7576969b2f402dea30a71bbf6e6 Mon Sep 17 00:00:00 2001
From: Nirbheek Chauhan <nirbheek@centricular.com>
Date: Sun, 26 May 2019 17:30:12 +0200
Subject: [PATCH] compositor: Skip the background when not visible

We don't need to waste time drawing the background when one of the
pads completely covers the output and there's no alpha on the pad or
in the video format. Speedups:

I420 1080p ! compositor ! fakesink - 72% faster
I420 1080p ! compositor background=black ! fakesink - 45% faster
---
 gst/compositor/compositor.c | 78 ++++++++++++++++++++++++++++++++-------------
 1 file changed, 55 insertions(+), 23 deletions(-)

diff --git a/gst/compositor/compositor.c b/gst/compositor/compositor.c
index aeba973..fee1936 100644
--- a/gst/compositor/compositor.c
+++ b/gst/compositor/compositor.c
@@ -313,13 +313,14 @@ clamp_rectangle (gint x, gint y, gint w, gint h, gint outer_width,
 
 /* Call this with the lock taken */
 static gboolean
-_pad_obscures_rectangle (GstVideoAggregatorPad * pad, GstVideoRectangle rect)
+_pad_obscures_rectangle (GstVideoAggregator * vagg, GstVideoAggregatorPad * pad,
+    GstVideoRectangle rect)
 {
   GstVideoRectangle pad_rect;
   GstCompositorPad *cpad = GST_COMPOSITOR_PAD (pad);
 
   /* No buffer to obscure the rectangle with */
-  if (gst_video_aggregator_pad_has_current_buffer (pad))
+  if (!gst_video_aggregator_pad_has_current_buffer (pad))
     return FALSE;
 
   /* Can't obscure if it's transparent and if the format has an alpha component
@@ -349,7 +350,6 @@ gst_compositor_pad_prepare_frame (GstVideoAggregatorPad * pad,
     GstVideoAggregator * vagg, GstBuffer * buffer,
     GstVideoFrame * prepared_frame)
 {
-  GstCompositor *comp = GST_COMPOSITOR (vagg);
   GstCompositorPad *cpad = GST_COMPOSITOR_PAD (pad);
   gint width, height;
   gboolean frame_obscured = FALSE;
@@ -393,7 +393,7 @@ gst_compositor_pad_prepare_frame (GstVideoAggregatorPad * pad,
    * higher-zorder frames */
   l = g_list_find (GST_ELEMENT (vagg)->sinkpads, pad)->next;
   for (; l; l = l->next) {
-    if (_pad_obscures_rectangle (l->data, frame_rect)) {
+    if (_pad_obscures_rectangle (vagg, l->data, frame_rect)) {
       frame_obscured = TRUE;
       break;
     }
@@ -417,7 +417,6 @@ static void
 gst_compositor_pad_create_conversion_info (GstVideoAggregatorConvertPad * pad,
     GstVideoAggregator * vagg, GstVideoInfo * conversion_info)
 {
-  GstCompositor *comp = GST_COMPOSITOR (vagg);
   GstCompositorPad *cpad = GST_COMPOSITOR_PAD (pad);
   gint width, height;
 
@@ -837,33 +836,48 @@ _negotiated_caps (GstAggregator * agg, GstCaps * caps)
   return GST_AGGREGATOR_CLASS (parent_class)->negotiated_src_caps (agg, caps);
 }
 
-static GstFlowReturn
-gst_compositor_aggregate_frames (GstVideoAggregator * vagg, GstBuffer * outbuf)
+static gboolean
+_should_draw_background (GstVideoAggregator * vagg)
 {
-  GList *l;
-  GstCompositor *self = GST_COMPOSITOR (vagg);
-  BlendFunction composite;
-  GstVideoFrame out_frame, *outframe;
+  GstVideoRectangle bg_rect;
+  gboolean draw = TRUE;
+  bg_rect.x = bg_rect.y = 0;
 
-  if (!gst_video_frame_map (&out_frame, &vagg->info, outbuf, GST_MAP_WRITE)) {
-    GST_WARNING_OBJECT (vagg, "Could not map output buffer");
-    return GST_FLOW_ERROR;
+  GST_OBJECT_LOCK (vagg);
+  bg_rect.w = GST_VIDEO_INFO_WIDTH (&vagg->info);
+  bg_rect.h = GST_VIDEO_INFO_HEIGHT (&vagg->info);
+  /* Check if the background is completely obscured by a pad
+   * TODO: Also skip if it's obscured by a combination of pads */
+  for (GList * l = GST_ELEMENT (vagg)->sinkpads; l; l = l->next) {
+    if (_pad_obscures_rectangle (vagg, l->data, bg_rect)) {
+      draw = FALSE;
+      break;
+    }
   }
+  GST_OBJECT_UNLOCK (vagg);
+  return draw;
+}
 
-  outframe = &out_frame;
-  /* default to blending */
-  composite = self->blend;
-  /* TODO: If the frames to be composited completely obscure the background,
+static BlendFunction
+_draw_background (GstVideoAggregator * vagg, GstVideoFrame * outframe)
+{
+  GstCompositor *comp = GST_COMPOSITOR (vagg);
+  BlendFunction composite = comp->blend;
+
+  /* If one of the frames to be composited completely obscures the background,
    * don't bother drawing the background at all. */
-  switch (self->background) {
+  if (!_should_draw_background (vagg))
+    return composite;
+
+  switch (comp->background) {
     case COMPOSITOR_BACKGROUND_CHECKER:
-      self->fill_checker (outframe);
+      comp->fill_checker (outframe);
       break;
     case COMPOSITOR_BACKGROUND_BLACK:
-      self->fill_color (outframe, 16, 128, 128);
+      comp->fill_color (outframe, 16, 128, 128);
       break;
     case COMPOSITOR_BACKGROUND_WHITE:
-      self->fill_color (outframe, 240, 128, 128);
+      comp->fill_color (outframe, 240, 128, 128);
       break;
     case COMPOSITOR_BACKGROUND_TRANSPARENT:
     {
@@ -885,11 +899,29 @@ gst_compositor_aggregate_frames (GstVideoAggregator * vagg, GstBuffer * outbuf)
         }
       }
       /* use overlay to keep background transparent */
-      composite = self->overlay;
+      composite = comp->overlay;
       break;
     }
   }
 
+  return composite;
+}
+
+static GstFlowReturn
+gst_compositor_aggregate_frames (GstVideoAggregator * vagg, GstBuffer * outbuf)
+{
+  GList *l;
+  BlendFunction composite;
+  GstVideoFrame out_frame, *outframe;
+
+  if (!gst_video_frame_map (&out_frame, &vagg->info, outbuf, GST_MAP_WRITE)) {
+    GST_WARNING_OBJECT (vagg, "Could not map output buffer");
+    return GST_FLOW_ERROR;
+  }
+
+  outframe = &out_frame;
+  composite = _draw_background (vagg, outframe);
+
   GST_OBJECT_LOCK (vagg);
   for (l = GST_ELEMENT (vagg)->sinkpads; l; l = l->next) {
     GstVideoAggregatorPad *pad = l->data;
-- 
2.7.4