monitor-manager: Add support for suggested position for outputs

In recent versions of the QXL driver, it may set "suggested X|Y" connector
properties. These properties are used to indicate the position at which
multiple displays should be aligned.  If all outputs have a suggested position,
the displays are arranged according to these positions, otherwise we fall back
to the default configuration.

At the moment, we trust that the driver has chosen sane values for the
suggested position.

src/backends/meta-monitor-config.c

@@ -34,6 +34,7 @@
 
 #include "config.h"
 
+#include "boxes-private.h"
 #include "meta-monitor-config.h"
 
 #include <string.h>
@@ -1096,6 +1097,55 @@ init_config_from_preferred_mode (MetaOutputConfig *config,
   config->is_presentation = FALSE;
 }
 
+/* This function handles configuring the outputs when the driver provides a
+ * suggested layout position for each output. This is done in recent versions
+ * of qxl and allows displays to be aligned on the guest in the same order as
+ * they are aligned on the client.
+ */
+static gboolean
+make_suggested_config (MetaMonitorConfig *self,
+                       MetaOutput        *outputs,
+                       unsigned           n_outputs,
+                       int                max_width,
+                       int                max_height,
+                       MetaConfiguration *config)
+{
+  unsigned int i;
+  MetaOutput *primary;
+  GList *region = NULL;
+
+  g_return_if_fail (config != NULL);
+  primary = find_primary_output (outputs, n_outputs);
+
+  for (i = 0; i < n_outputs; i++)
+    {
+      gboolean is_primary = (&outputs[i] == primary);
+
+      if (outputs[i].suggested_x < 0 || outputs[i].suggested_y < 0)
+          return FALSE;
+
+      init_config_from_preferred_mode (&config->outputs[i], &outputs[i]);
+      config->outputs[i].is_primary = is_primary;
+
+      config->outputs[i].rect.x = outputs[i].suggested_x;
+      config->outputs[i].rect.y = outputs[i].suggested_y;
+
+      /* Reject the configuration if the suggested positions result in
+       * overlapping displays */
+      if (meta_rectangle_overlaps_with_region (region, &config->outputs[i].rect))
+        {
+          g_warning ("Overlapping outputs, rejecting suggested configuration");
+          g_list_free (region);
+          return FALSE;
+        }
+
+      region = g_list_prepend (region, &config->outputs[i].rect);
+    }
+
+  g_list_free (region);
+  return TRUE;
+}
+
 static void
 make_linear_config (MetaMonitorConfig *self,
                     MetaOutput        *outputs,
@@ -1228,6 +1278,9 @@ make_default_config (MetaMonitorConfig *self,
       return ret;
     }
 
+  if (make_suggested_config (self, outputs, n_outputs, max_width, max_height, ret))
+      return ret;
+
   if (use_stored_config &&
       extend_stored_config (self, outputs, n_outputs, max_width, max_height, ret))
       return ret;

src/backends/meta-monitor-manager.h

@@ -116,6 +116,8 @@ struct _MetaOutput
 
   /* get a new preferred mode on hotplug events, to handle dynamic guest resizing */
   gboolean hotplug_mode_update;
+  gint suggested_x;
+  gint suggested_y;
 };
 
 struct _MetaCRTC

src/backends/native/meta-monitor-manager-kms.c

@@ -415,6 +415,8 @@ meta_monitor_manager_kms_read_current (MetaMonitorManager *manager)
 	  meta_output->name = make_output_name (connector);
 	  meta_output->width_mm = connector->mmWidth;
 	  meta_output->height_mm = connector->mmHeight;
+	  meta_output->suggested_x = -1;
+	  meta_output->suggested_y = -1;
 
           switch (connector->subpixel)
             {

src/backends/x11/meta-monitor-manager-xrandr.c

@@ -139,6 +139,34 @@ meta_monitor_transform_from_xrandr_all (Rotation rotation)
   return ret;
 }
 
+static gboolean
+output_get_integer_property (MetaMonitorManagerXrandr *manager_xrandr,
+                             MetaOutput *output, const char *propname,
+                             gint *value)
+{
+  gboolean exists = FALSE;
+  Atom atom, actual_type;
+  int actual_format;
+  unsigned long nitems, bytes_after;
+  unsigned char *buffer;
+
+  atom = XInternAtom (manager_xrandr->xdisplay, propname, False);
+  XRRGetOutputProperty (manager_xrandr->xdisplay,
+                        (XID)output->winsys_id,
+                        atom,
+                        0, G_MAXLONG, False, False, XA_INTEGER,
+                        &actual_type, &actual_format,
+                        &nitems, &bytes_after, &buffer);
+
+  exists = (actual_type == XA_INTEGER && actual_format == 32 && nitems == 1);
+
+  if (exists && value != NULL)
+    *value = ((int*)buffer)[0];
+
+  XFree (buffer);
+  return exists;
+}
+
 static gboolean
 output_get_property_exists (MetaMonitorManagerXrandr *manager_xrandr,
                             MetaOutput *output, const char *propname)
@@ -356,6 +384,28 @@ output_get_hotplug_mode_update (MetaMonitorManagerXrandr *manager_xrandr,
   return output_get_property_exists (manager_xrandr, output, "hotplug_mode_update");
 }
 
+static gint
+output_get_suggested_x (MetaMonitorManagerXrandr *manager_xrandr,
+                        MetaOutput               *output)
+{
+  gint val;
+  if (output_get_integer_property (manager_xrandr, output, "suggested X", &val))
+    return val;
+
+  return -1;
+}
+
+static gint
+output_get_suggested_y (MetaMonitorManagerXrandr *manager_xrandr,
+                        MetaOutput               *output)
+{
+  gint val;
+  if (output_get_integer_property (manager_xrandr, output, "suggested Y", &val))
+    return val;
+
+  return -1;
+}
+
 static char *
 get_xmode_name (XRRModeInfo *xmode)
 {
@@ -543,6 +593,8 @@ meta_monitor_manager_xrandr_read_current (MetaMonitorManager *manager)
 	  meta_output->height_mm = output->mm_height;
 	  meta_output->subpixel_order = COGL_SUBPIXEL_ORDER_UNKNOWN;
           meta_output->hotplug_mode_update = output_get_hotplug_mode_update (manager_xrandr, meta_output);
+	  meta_output->suggested_x = output_get_suggested_x (manager_xrandr, meta_output);
+	  meta_output->suggested_y = output_get_suggested_y (manager_xrandr, meta_output);
 
 	  meta_output->n_modes = output->nmode;
 	  meta_output->modes = g_new0 (MetaMonitorMode *, meta_output->n_modes);