From 921417138f3c4c36b703e05f05ba69a42079bec6 Mon Sep 17 00:00:00 2001
From: Nirbheek Chauhan <nirbheek@centricular.com>
Date: Fri, 14 Jun 2019 02:32:50 +0530
Subject: [PATCH] compositor: Copy frames as-is when possible

The blend functions for alpha formats need to do more work than just
doing a memcpy, so we can do a memcpy when we know that a blend is not
actually needed.

1080p AYUV ! compositor background=transparent ! fakesink - 56% faster

Specifically, when we don't draw the background and the first pad we
draw completely covers the output frame, we can just copy it as-is.
The rest of the pads (if any) will get composited on top normally.
---
 gst/compositor/compositor.c | 44 ++++++++++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 10 deletions(-)

diff --git a/gst/compositor/compositor.c b/gst/compositor/compositor.c
index 9332bdc..09f970f 100644
--- a/gst/compositor/compositor.c
+++ b/gst/compositor/compositor.c
@@ -863,19 +863,20 @@ _should_draw_background (GstVideoAggregator * vagg, gboolean bg_transparent)
   return draw;
 }
 
-static BlendFunction
-_draw_background (GstVideoAggregator * vagg, GstVideoFrame * outframe)
+static gboolean
+_draw_background (GstVideoAggregator * vagg, GstVideoFrame * outframe,
+    BlendFunction * composite)
 {
   GstCompositor *comp = GST_COMPOSITOR (vagg);
-  BlendFunction composite = comp->blend;
 
+  *composite = comp->blend;
   /* If one of the frames to be composited completely obscures the background,
    * don't bother drawing the background at all. We can also always use the
    * 'blend' BlendFunction in that case because it only changes if we have to
    * overlay on top of a transparent background. */
   if (!_should_draw_background (vagg,
           comp->background == COMPOSITOR_BACKGROUND_TRANSPARENT))
-    return composite;
+    return FALSE;
 
   switch (comp->background) {
     case COMPOSITOR_BACKGROUND_CHECKER:
@@ -907,12 +908,24 @@ _draw_background (GstVideoAggregator * vagg, GstVideoFrame * outframe)
         }
       }
       /* use overlay to keep background transparent */
-      composite = comp->overlay;
+      *composite = comp->overlay;
       break;
     }
   }
 
-  return composite;
+  return TRUE;
+}
+
+static gboolean
+frames_can_copy (const GstVideoFrame * frame1, const GstVideoFrame * frame2)
+{
+  if (GST_VIDEO_FRAME_FORMAT (frame1) != GST_VIDEO_FRAME_FORMAT (frame2))
+    return FALSE;
+  if (GST_VIDEO_FRAME_HEIGHT (frame1) != GST_VIDEO_FRAME_HEIGHT (frame2))
+    return FALSE;
+  if (GST_VIDEO_FRAME_WIDTH (frame1) != GST_VIDEO_FRAME_WIDTH (frame2))
+    return FALSE;
+  return TRUE;
 }
 
 static GstFlowReturn
@@ -921,6 +934,8 @@ gst_compositor_aggregate_frames (GstVideoAggregator * vagg, GstBuffer * outbuf)
   GList *l;
   BlendFunction composite;
   GstVideoFrame out_frame, *outframe;
+  gboolean drew_background;
+  guint drawn_pads = 0;
 
   if (!gst_video_frame_map (&out_frame, &vagg->info, outbuf, GST_MAP_WRITE)) {
     GST_WARNING_OBJECT (vagg, "Could not map output buffer");
@@ -928,7 +943,7 @@ gst_compositor_aggregate_frames (GstVideoAggregator * vagg, GstBuffer * outbuf)
   }
 
   outframe = &out_frame;
-  composite = _draw_background (vagg, outframe);
+  drew_background = _draw_background (vagg, outframe, &composite);
 
   GST_OBJECT_LOCK (vagg);
   for (l = GST_ELEMENT (vagg)->sinkpads; l; l = l->next) {
@@ -954,9 +969,18 @@ gst_compositor_aggregate_frames (GstVideoAggregator * vagg, GstBuffer * outbuf)
     }
 
     if (prepared_frame != NULL) {
-      composite (prepared_frame,
-          compo_pad->xpos,
-          compo_pad->ypos, compo_pad->alpha, outframe, blend_mode);
+      /* If this is the first pad we're drawing, and we didn't draw the
+       * background, and @prepared_frame has the same format, height, and width
+       * as @outframe, then we can just copy it as-is. Subsequent pads (if any)
+       * will be composited on top of it. */
+      if (drawn_pads == 0 && !drew_background &&
+          frames_can_copy (prepared_frame, outframe))
+        gst_video_frame_copy (outframe, prepared_frame);
+      else
+        composite (prepared_frame,
+            compo_pad->xpos,
+            compo_pad->ypos, compo_pad->alpha, outframe, blend_mode);
+      drawn_pads++;
     }
   }
   GST_OBJECT_UNLOCK (vagg);
-- 
2.7.4