[libcamera-devel] [PATCH] gstreamer: Fix usage of default size for fixation

[Nicolas Dufresne]

From: Nicolas Dufresne <nicolas.dufresne at collabora.com>

Even thought this is not formaly documented, all pipeline managers sets a
default value to StreamConfiguration::size. The original fixation code was
attempting to use it, but as it was truncating the caps to its first structure
it would never actually find a best match.

In this patch, instead of truncating, we weight various matches using the
product of the width and height delta. We also split delta from ranges
appart and prefer fixed size over them as ranges are not reliable.

This patch also removes the related todo, as it seems that libcamera core won't
go further then providing this default value and won't be sorting the format and
size lists.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>
---
 src/gstreamer/gstlibcamera-utils.cpp | 51 +++++++++++++++++++++++++---
 src/gstreamer/gstlibcamerasrc.cpp    |  4 ---
 2 files changed, 47 insertions(+), 8 deletions(-)

diff --git a/src/gstreamer/gstlibcamera-utils.cpp b/src/gstreamer/gstlibcamera-utils.cpp
index 61370d5f..007d6a64 100644
--- a/src/gstreamer/gstlibcamera-utils.cpp
+++ b/src/gstreamer/gstlibcamera-utils.cpp
@@ -136,14 +136,57 @@ gst_libcamera_configure_stream_from_caps(StreamConfiguration &stream_cfg,
 					 GstCaps *caps)
 {
 	GstVideoFormat gst_format = pixel_format_to_gst_format(stream_cfg.pixelFormat);
+	guint i;
+	gint best_fixed = -1, best_in_range = -1;
+	GstStructure *s;
+
+	/*
+	 * These are delta weight computed from:
+	 *   ABS(width - stream_cfg.size.width) * ABS(height - stream_cfg.size.height)
+	 */
+	guint best_fixed_delta = G_MAXUINT;
+	guint best_in_range_delta = G_MAXUINT;
 
 	/* First fixate the caps using default configuration value. */
 	g_assert(gst_caps_is_writable(caps));
-	caps = gst_caps_truncate(caps);
-	GstStructure *s = gst_caps_get_structure(caps, 0);
 
-	gst_structure_fixate_field_nearest_int(s, "width", stream_cfg.size.width);
-	gst_structure_fixate_field_nearest_int(s, "height", stream_cfg.size.height);
+	/* Lookup the structure for a close match to the stream_cfg.size */
+	for (i = 0; i < gst_caps_get_size(caps); i++) {
+		s = gst_caps_get_structure(caps, i);
+		gint width, height;
+		guint delta;
+
+		if (gst_structure_has_field_typed(s, "width", G_TYPE_INT) &&
+		    gst_structure_has_field_typed(s, "height", G_TYPE_INT)) {
+			gst_structure_get_int(s, "width", &width);
+			gst_structure_get_int(s, "width", &height);
+
+			delta = ABS(width - (gint)stream_cfg.size.width) * ABS(height - (gint)stream_cfg.size.height);
+
+			if (delta < best_fixed_delta) {
+				best_fixed_delta = delta;
+				best_fixed = i;
+			}
+		} else {
+			gst_structure_fixate_field_nearest_int(s, "width", stream_cfg.size.width);
+			gst_structure_fixate_field_nearest_int(s, "height", stream_cfg.size.height);
+			gst_structure_get_int(s, "width", &width);
+			gst_structure_get_int(s, "width", &height);
+
+			delta = ABS(width - (gint)stream_cfg.size.width) * ABS(height - (gint)stream_cfg.size.height);
+
+			if (delta < best_in_range_delta) {
+				best_in_range_delta = delta;
+				best_in_range = i;
+			}
+		}
+	}
+
+	/* Prefer reliable fixed value over ranges */
+	if (best_fixed >= 0)
+		s = gst_caps_get_structure(caps, best_fixed);
+	else
+		s = gst_caps_get_structure(caps, best_in_range);
 
 	if (gst_structure_has_name(s, "video/x-raw")) {
 		const gchar *format = gst_video_format_to_string(gst_format);
diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
index b243aeb3..4c7b36ae 100644
--- a/src/gstreamer/gstlibcamerasrc.cpp
+++ b/src/gstreamer/gstlibcamerasrc.cpp
@@ -25,10 +25,6 @@
  *  - Add timestamp support
  *  - Use unique names to select the camera devices
  *  - Add GstVideoMeta support (strides and offsets)
- *
- * \todo libcamera UVC drivers picks the lowest possible resolution first, this
- * should be fixed so that we get a decent resolution and framerate for the
- * role by default.
  */
 
 #include "gstlibcamerasrc.h"
-- 
2.31.1