kmssink: calculate display ratio

Get the aspect ratio given the information provided by libdrm, and with it
calculate the display ratio.

https://bugzilla.gnome.org/show_bug.cgi?id=761059

sys/kms/gstkmssink.c

@@ -381,6 +381,12 @@ gst_kms_sink_start (GstBaseSink * bsink)
   self->hdisplay = crtc->mode.hdisplay;
   self->vdisplay = crtc->mode.vdisplay;
 
+  self->mm_width = conn->mmWidth;
+  self->mm_height = conn->mmHeight;
+
+  GST_INFO_OBJECT (self, "display size: pixels = %dx%d / millimeters = %dx%d",
+      self->hdisplay, self->vdisplay, self->mm_width, self->mm_height);
+
   ret = TRUE;
 
 bail:
@@ -534,6 +540,57 @@ config_failed:
   }
 }
 
+static gboolean
+gst_kms_sink_calculate_display_ratio (GstKMSSink * self, GstVideoInfo * vinfo)
+{
+  guint dar_n, dar_d;
+  guint video_width, video_height;
+  guint video_par_n, video_par_d;
+  guint dpy_par_n, dpy_par_d;
+
+  video_width = GST_VIDEO_INFO_WIDTH (vinfo);
+  video_height = GST_VIDEO_INFO_HEIGHT (vinfo);
+  video_par_n = GST_VIDEO_INFO_PAR_N (vinfo);
+  video_par_d = GST_VIDEO_INFO_PAR_D (vinfo);
+
+  gst_video_calculate_device_ratio (self->hdisplay, self->vdisplay,
+      self->mm_width, self->mm_height, &dpy_par_n, &dpy_par_d);
+
+  if (!gst_video_calculate_display_ratio (&dar_n, &dar_d, video_width,
+          video_height, video_par_n, video_par_d, dpy_par_n, dpy_par_d))
+    return FALSE;
+
+  GST_DEBUG_OBJECT (self, "video calculated display ratio: %d/%d", dar_n,
+      dar_d);
+
+  /* now find a width x height that respects this display ratio.
+   * prefer those that have one of w/h the same as the incoming video
+   * using wd / hd = dar_n / dar_d */
+
+  /* start with same height, because of interlaced video */
+  /* check hd / dar_d is an integer scale factor, and scale wd with the PAR */
+  if (video_height % dar_d == 0) {
+    GST_DEBUG_OBJECT (self, "keeping video height");
+    GST_VIDEO_SINK_WIDTH (self) = (guint)
+        gst_util_uint64_scale_int (video_height, dar_n, dar_d);
+    GST_VIDEO_SINK_HEIGHT (self) = video_height;
+  } else if (video_width % dar_n == 0) {
+    GST_DEBUG_OBJECT (self, "keeping video width");
+    GST_VIDEO_SINK_WIDTH (self) = video_width;
+    GST_VIDEO_SINK_HEIGHT (self) = (guint)
+        gst_util_uint64_scale_int (video_width, dar_d, dar_n);
+  } else {
+    GST_DEBUG_OBJECT (self, "approximating while keeping video height");
+    GST_VIDEO_SINK_WIDTH (self) = (guint)
+        gst_util_uint64_scale_int (video_height, dar_n, dar_d);
+    GST_VIDEO_SINK_HEIGHT (self) = video_height;
+  }
+  GST_DEBUG_OBJECT (self, "scaling to %dx%d", GST_VIDEO_SINK_WIDTH (self),
+      GST_VIDEO_SINK_HEIGHT (self));
+
+  return TRUE;
+}
+
 static gboolean
 gst_kms_sink_set_caps (GstBaseSink * bsink, GstCaps * caps)
 {
@@ -546,8 +603,8 @@ gst_kms_sink_set_caps (GstBaseSink * bsink, GstCaps * caps)
   if (!gst_video_info_from_caps (&vinfo, caps))
     goto invalid_format;
 
-  GST_VIDEO_SINK_WIDTH (self) = GST_VIDEO_INFO_WIDTH (&vinfo);
+  if (!gst_kms_sink_calculate_display_ratio (self, &vinfo))
-  GST_VIDEO_SINK_HEIGHT (self) = GST_VIDEO_INFO_HEIGHT (&vinfo);
+    goto no_disp_ratio;
 
   if (GST_VIDEO_SINK_WIDTH (self) <= 0 || GST_VIDEO_SINK_HEIGHT (self) <= 0)
     goto invalid_size;
@@ -586,6 +643,13 @@ invalid_size:
         ("Invalid image size."));
     return FALSE;
   }
+
+no_disp_ratio:
+  {
+    GST_ELEMENT_ERROR (self, CORE, NEGOTIATION, (NULL),
+        ("Error calculating the output display ratio of the video."));
+    return FALSE;
+  }
 no_pool:
   {
     /* Already warned in create_pool */

sys/kms/gstkmsutils.c

@@ -121,3 +121,56 @@ gst_kms_sink_caps_template_fill (void)
   }
   return gst_caps_simplify (caps);
 }
+
+static const gint device_par_map[][2] = {
+  {1, 1},                       /* regular screen */
+  {16, 15},                     /* PAL TV */
+  {11, 10},                     /* 525 line Rec.601 video */
+  {54, 59},                     /* 625 line Rec.601 video */
+  {64, 45},                     /* 1280x1024 on 16:9 display */
+  {5, 3},                       /* 1280x1024 on 4:3 display */
+  {4, 3}                        /* 800x600 on 16:9 display */
+};
+
+#define DELTA(ratio, idx, w) \
+  (ABS(ratio - ((gdouble)device_par_map[idx][w] / device_par_map[idx][!(w)])))
+
+void
+gst_video_calculate_device_ratio (guint dev_width, guint dev_height,
+    guint dev_width_mm, guint dev_height_mm,
+    guint * dpy_par_n, guint * dpy_par_d)
+{
+  gdouble ratio, delta, cur_delta;
+  gint i, j, index, windex;
+
+  /* First, calculate the "real" ratio based on the X values; which is
+   * the "physical" w/h divided by the w/h in pixels of the display */
+  if (dev_width == 0 || dev_height == 0
+      || dev_width_mm == 0 || dev_height_mm == 0)
+    ratio = 1.0;
+  else
+    ratio = (gdouble) (dev_width_mm * dev_height) / (dev_height_mm * dev_width);
+
+  /* Now, find the one from device_par_map[][2] with the lowest delta
+   * to the real one */
+  delta = DELTA (ratio, 0, 0);
+  index = 0;
+  windex = 0;
+
+  for (i = 1; i < G_N_ELEMENTS (device_par_map); i++) {
+    for (j = 0; j < 2; j++) {
+      cur_delta = DELTA (ratio, i, j);
+      if (cur_delta < delta) {
+        index = i;
+        windex = j;
+        delta = cur_delta;
+      }
+    }
+  }
+
+  if (dpy_par_n)
+    *dpy_par_n = device_par_map[index][windex];
+
+  if (dpy_par_d)
+    *dpy_par_d = device_par_map[index][windex ^ 1];
+}

sys/kms/gstkmsutils.h

@@ -33,6 +33,12 @@ G_BEGIN_DECLS
 GstVideoFormat gst_video_format_from_drm (guint32 drmfmt);
 guint32        gst_drm_format_from_video (GstVideoFormat fmt);
 GstCaps *      gst_kms_sink_caps_template_fill (void);
+void           gst_video_calculate_device_ratio (guint dev_width,
+						 guint dev_height,
+						 guint dev_width_mm,
+						 guint dev_height_mm,
+						 guint * dpy_par_n,
+						 guint * dpy_par_d);
 
 G_END_DECLS