Remove ambient-sensor tolerance check, expose and document target

brightness tolerance.

We can't rely on values from the sensor proxy - units may differ
depending on hardware. We can dampen our responses to changes by
only adjusting the backlight when it would be more than a minor
percentage adjustment.

Author: mtwebster

plugins/power/csd-power-manager.c

@@ -121,17 +121,17 @@ abs_to_percentage (int min, int max, int value)
 /* Interval between transition steps (ms). */
 #define AMBIENT_TRANSITION_STEP_MS      (AMBIENT_TRANSITION_DURATION_MS / AMBIENT_TRANSITION_STEPS)
 
-/* Relative tolerance for considering two sensor readings "equal". */
-#define AMBIENT_SENSOR_TOLERANCE        0.05
-
 /* After a transition completes, ignore sensor changes for this long (ms)
  * to let the sensor settle with the new screen brightness. */
 #define AMBIENT_POST_TRANSITION_DEAD_ZONE_MS    500
 
+/* Minimum brightness change (%) required to trigger a transition. */
+#define AMBIENT_MIN_BRIGHTNESS_CHANGE   5.0
+
 /* How much of the computed sensor-to-brightness ratio to actually apply.
  * 1.0 = full response, 0.5 = half, etc. Lower values reduce feedback from
  * screen content affecting the sensor. */
-#define AMBIENT_RESPONSE_DAMPENING      0.75
+#define AMBIENT_RESPONSE_DAMPENING      0.8
 
 #define CSD_POWER_MANAGER_GET_PRIVATE(o) (G_TYPE_INSTANCE_GET_PRIVATE ((o), CSD_TYPE_POWER_MANAGER, CsdPowerManagerPrivate))
 
@@ -3701,14 +3701,6 @@ engine_settings_key_changed_cb (GSettings *settings,
         }
 }
 
-static gboolean
-ambient_sensors_equal (gdouble a, gdouble b)
-{
-        if (a <= 0.0)
-                return FALSE;
-        return fabs (a - b) / a < AMBIENT_SENSOR_TOLERANCE;
-}
-
 static void
 ambient_cancel_timers (CsdPowerManager *manager)
 {
@@ -3805,7 +3797,7 @@ ambient_begin_transition (CsdPowerManager *manager, gdouble target_brightness)
 {
         gdouble current = manager->priv->ambient_brightness_baseline;
 
-        if (fabs (target_brightness - current) < 1.0) {
+        if (fabs (target_brightness - current) < AMBIENT_MIN_BRIGHTNESS_CHANGE) {
                 g_debug ("Ambient target %.1f%% too close to current %.1f%%, skipping",
                          target_brightness, current);
                 manager->priv->ambient_state = AMBIENT_STATE_IDLE;
@@ -3903,7 +3895,7 @@ iio_proxy_changed (CsdPowerManager *manager)
 
         switch (manager->priv->ambient_state) {
         case AMBIENT_STATE_IDLE:
-                if (ambient_sensors_equal (manager->priv->ambient_baseline_sensor, sensor_value))
+                if (sensor_value == manager->priv->ambient_baseline_sensor)
                         return;
 
                 g_debug ("Ambient: sensor changed from %f to %f, starting stabilization",
@@ -3918,14 +3910,14 @@ iio_proxy_changed (CsdPowerManager *manager)
                 break;
 
         case AMBIENT_STATE_STABILIZING:
-                if (ambient_sensors_equal (manager->priv->ambient_baseline_sensor, sensor_value)) {
+                if (sensor_value == manager->priv->ambient_baseline_sensor) {
                         g_debug ("Ambient: sensor returned to baseline, cancelling");
                         ambient_cancel_timers (manager);
                         manager->priv->ambient_state = AMBIENT_STATE_IDLE;
                         return;
                 }
 
-                if (!ambient_sensors_equal (manager->priv->ambient_pending_sensor, sensor_value)) {
+                if (sensor_value != manager->priv->ambient_pending_sensor) {
                         g_debug ("Ambient: sensor changed during stabilization (%f -> %f), restarting",
                                  manager->priv->ambient_pending_sensor, sensor_value);
                         if (manager->priv->ambient_stabilize_timer_id > 0)