libsysprof-gtk: add pathological check for axis

That way we don't give values back that will not make any sense.

src/libsysprof-gtk/sysprof-axis-private.h

@@ -34,10 +34,11 @@ struct _SysprofAxisClass
 {
   GObjectClass parent_class;
 
-  void   (*get_min_value) (SysprofAxis  *axis,
-                           GValue       *min_value);
-  double (*normalize)     (SysprofAxis  *axis,
-                           const GValue *value);
+  void     (*get_min_value)   (SysprofAxis  *axis,
+                               GValue       *min_value);
+  double   (*normalize)       (SysprofAxis  *axis,
+                               const GValue *value);
+  gboolean (*is_pathological) (SysprofAxis  *axis);
 };
 
 #define SYSPROF_AXIS_GET_CLASS(obj) G_TYPE_INSTANCE_GET_CLASS(obj, SYSPROF_TYPE_AXIS, SysprofAxisClass)
@@ -56,6 +57,15 @@ _sysprof_axis_normalize (SysprofAxis  *axis,
   return SYSPROF_AXIS_GET_CLASS (axis)->normalize (axis, value);
 }
 
+static inline double
+_sysprof_axis_is_pathological (SysprofAxis *axis)
+{
+  if (SYSPROF_AXIS_GET_CLASS (axis)->is_pathological)
+    return SYSPROF_AXIS_GET_CLASS (axis)->is_pathological (axis);
+
+  return FALSE;
+}
+
 void _sysprof_axis_emit_range_changed (SysprofAxis *self);
 
 G_END_DECLS

src/libsysprof-gtk/sysprof-value-axis.c

@@ -105,6 +105,14 @@ sysprof_value_axis_normalize (SysprofAxis  *axis,
   return r;
 }
 
+static gboolean
+sysprof_value_axis_is_pathological (SysprofAxis *axis)
+{
+  SysprofValueAxis *self = SYSPROF_VALUE_AXIS (axis);
+
+  return self->min_value == self->max_value;
+}
+
 static void
 sysprof_value_axis_get_property (GObject    *object,
                                  guint       prop_id,
@@ -162,6 +170,7 @@ sysprof_value_axis_class_init (SysprofValueAxisClass *klass)
 
   axis_class->get_min_value = sysprof_value_axis_real_get_min_value;
   axis_class->normalize = sysprof_value_axis_normalize;
+  axis_class->is_pathological = sysprof_value_axis_is_pathological;
 
   properties[PROP_MIN_VALUE] =
     g_param_spec_double ("min-value", NULL, NULL,

src/libsysprof-gtk/sysprof-xy-layer.c

@@ -20,6 +20,7 @@
 
 #include "config.h"
 
+#include "sysprof-axis-private.h"
 #include "sysprof-xy-layer-private.h"
 
 enum {
@@ -192,6 +193,16 @@ _sysprof_xy_layer_get_xy (SysprofXYLayer  *self,
   g_return_if_fail (y_values != NULL);
   g_return_if_fail (n_values != NULL);
 
+  if (self->x_axis == NULL || _sysprof_axis_is_pathological (self->x_axis) ||
+      self->y_axis == NULL || _sysprof_axis_is_pathological (self->y_axis))
+    {
+      *n_values = 0;
+      *x_values = NULL;
+      *y_values = NULL;
+
+      return;
+    }
+
   *x_values = sysprof_normalized_series_get_values (self->normal_x, &n_x_values);
   *y_values = sysprof_normalized_series_get_values (self->normal_y, &n_y_values);
   *n_values = MIN (n_x_values, n_y_values);