From 648739012a1518f41a663c89805ff77829a51e28 Mon Sep 17 00:00:00 2001
From: Seungha Yang <seungha@centricular.com>
Date: Tue, 18 Jan 2022 21:21:23 +0900
Subject: [PATCH] compositor: Warn when inputs are SDR/HDR mixed

Let user know that the result of mixed SDR/HDR is not guaranteed
to be a good visual quality.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1486>
---
 .../gst/compositor/compositor.c               | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/subprojects/gst-plugins-base/gst/compositor/compositor.c b/subprojects/gst-plugins-base/gst/compositor/compositor.c
index 87637802af..54a2e9dc58 100644
--- a/subprojects/gst-plugins-base/gst/compositor/compositor.c
+++ b/subprojects/gst-plugins-base/gst/compositor/compositor.c
@@ -1389,6 +1389,10 @@ _negotiated_caps (GstAggregator * agg, GstCaps * caps)
   GstVideoAggregator *vagg = GST_VIDEO_AGGREGATOR (agg);
   GstVideoInfo v_info;
   guint n_threads;
+  GList *iter;
+  guint n_sdr = 0;
+  guint n_hlg = 0;
+  guint n_pq = 0;
 
   GST_DEBUG_OBJECT (agg, "Negotiated caps %" GST_PTR_FORMAT, caps);
 
@@ -1400,6 +1404,40 @@ _negotiated_caps (GstAggregator * agg, GstCaps * caps)
     return FALSE;
   }
 
+  GST_OBJECT_LOCK (vagg);
+  for (iter = GST_ELEMENT (vagg)->sinkpads; iter; iter = g_list_next (iter)) {
+    GstVideoAggregatorPad *pad = (GstVideoAggregatorPad *) iter->data;
+
+    if (!pad->info.finfo)
+      continue;
+
+    switch (pad->info.colorimetry.transfer) {
+      case GST_VIDEO_TRANSFER_SMPTE2084:
+        n_pq++;
+        break;
+      case GST_VIDEO_TRANSFER_ARIB_STD_B67:
+        n_hlg++;
+        break;
+      default:
+        n_sdr++;
+        break;
+    }
+  }
+  GST_OBJECT_UNLOCK (vagg);
+
+  /* TODO: we don't have support for HDR tone-mapping, so mixing HDR/SDR might
+   * result in somewhat visually bad image. Needs enhancement to the
+   * video-convert or somewhere */
+  if (n_sdr > 0) {
+    if (n_hlg > 0 || n_pq > 0) {
+      GST_ELEMENT_WARNING (compositor, STREAM, NOT_IMPLEMENTED,
+          ("Mixing SDR and HDR contents would result in color loss"), (NULL));
+    }
+  } else if (n_hlg > 0 && n_pq > 0) {
+    GST_ELEMENT_WARNING (compositor, STREAM, NOT_IMPLEMENTED,
+        ("Mixing HDR10 and HLG contents would result in color loss"), (NULL));
+  }
+
   if (compositor->max_threads == 0)
     n_threads = g_get_num_processors ();
   else