[mutter/wip/tablet-protocol-v2: 50/65] backends: Add function to apply pressure sensitivity to tablet tools

[Carlos Garnacho <carlosg src gnome org>]

commit c6b3447f94cd8fd903b43031d5ab9087c6076650
Author: Carlos Garnacho <carlosg gnome org>
Date:   Wed Jun 22 15:58:33 2016 +0200

    backends: Add function to apply pressure sensitivity to tablet tools
    
    A bezier curve is created out of the 2 control points in settings, so
    the pressure is made to follow the stablished curve between 0 and 1.

 src/backends/meta-input-settings-private.h |    5 ++
 src/backends/meta-input-settings.c         |   59 ++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 0 deletions(-)
---
diff --git a/src/backends/meta-input-settings-private.h b/src/backends/meta-input-settings-private.h
index 8131086..8c8fed6 100644
--- a/src/backends/meta-input-settings-private.h
+++ b/src/backends/meta-input-settings-private.h
@@ -110,6 +110,11 @@ GDesktopStylusButtonAction meta_input_settings_get_stylus_button_action (MetaInp
                                                                          ClutterInputDeviceTool *tool,
                                                                          ClutterInputDevice     
*current_device,
                                                                          guint                   button);
+gdouble                    meta_input_settings_translate_tablet_tool_pressure (MetaInputSettings      
*input_settings,
+                                                                               ClutterInputDeviceTool *tool,
+                                                                               ClutterInputDevice     
*current_tablet,
+                                                                               gdouble                 
pressure);
+
 #ifdef HAVE_LIBWACOM
 WacomDevice * meta_input_settings_get_tablet_wacom_device (MetaInputSettings *settings,
                                                            ClutterInputDevice *device);
diff --git a/src/backends/meta-input-settings.c b/src/backends/meta-input-settings.c
index 049d1b8..0fec343 100644
--- a/src/backends/meta-input-settings.c
+++ b/src/backends/meta-input-settings.c
@@ -1243,3 +1243,62 @@ meta_input_settings_get_tablet_wacom_device (MetaInputSettings *settings,
   return info->wacom_device;
 }
 #endif /* HAVE_LIBWACOM */
+
+static gdouble
+calculate_bezier_position (gdouble pos,
+                           gdouble x1,
+                           gdouble y1,
+                           gdouble x2,
+                           gdouble y2)
+{
+  gdouble int1_y, int2_y;
+
+  pos = CLAMP (pos, 0, 1);
+
+  /* Intersection between 0,0 and x1,y1 */
+  int1_y = pos * y1;
+
+  /* Intersection between x2,y2 and 1,1 */
+  int2_y = (pos * (1 - y2)) + y2;
+
+  /* Find the new position in the line traced by the previous points */
+  return (pos * (int2_y - int1_y)) + int1_y;
+}
+
+gdouble
+meta_input_settings_translate_tablet_tool_pressure (MetaInputSettings      *input_settings,
+                                                    ClutterInputDeviceTool *tool,
+                                                    ClutterInputDevice     *current_tablet,
+                                                    gdouble                 pressure)
+{
+  GSettings *settings;
+  GVariant *variant;
+  const gint32 *curve;
+  gsize n_elems;
+
+  pressure = CLAMP (pressure, 0, 1);
+
+  g_return_val_if_fail (META_IS_INPUT_SETTINGS (input_settings), pressure);
+  g_return_val_if_fail (CLUTTER_IS_INPUT_DEVICE_TOOL (tool), pressure);
+  g_return_val_if_fail (CLUTTER_IS_INPUT_DEVICE (current_tablet), pressure);
+
+  settings = lookup_tool_settings (tool, current_tablet);
+
+  if (clutter_input_device_tool_get_tool_type (tool) == CLUTTER_INPUT_DEVICE_TOOL_ERASER)
+    variant = g_settings_get_value (settings, "eraser-pressure-curve");
+  else
+    variant = g_settings_get_value (settings, "pressure-curve");
+
+  curve = g_variant_get_fixed_array (variant, &n_elems, sizeof (gint32));
+  if (n_elems != 4)
+    return pressure;
+
+  pressure = calculate_bezier_position (pressure,
+                                        (gdouble) curve[0] / 100,
+                                        (gdouble) curve[1] / 100,
+                                        (gdouble) curve[2] / 100,
+                                        (gdouble) curve[3] / 100);
+  g_variant_unref (variant);
+
+  return pressure;
+}