[ui][input-pipeline] gestures: enable drag recognizer

Enable the drag recognizer, by adding it to the set of
recognizers instantiated by `gesture_arena::make_input_handler`.

Along the way, rename `one_finger_drag::Contender` to
`one_finger_drag::InitialContender`, to match the naming
in other recognizers.

Note: after I release the touchpad button, the selected
text is no longer highlighted. I'll file a separate bug
to improve that.

Bug: None
Test: manual

Manual test
-----------
1. Opened an article in Wikipedia.
2. Pointed at a word.
3. Pressed touchpad down with one finger.
4. Moved finger until pointer was at end of sentence.
5. Saw that the text from the initial word to the end of the
   sentence was highlighted.

Change-Id: Ic46ccef2ce6f2431078a8961e91cf1888c7b2d5b
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/707546
Fuchsia-Auto-Submit: Mukesh Agrawal <quiche@google.com>
Reviewed-by: Jianpeng Chao <chaopeng@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>

Author: gquiche

src/ui/lib/input_pipeline/src/gestures/gesture_arena.rs

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 use {
-    super::{click, motion, primary_tap, secondary_tap},
+    super::{click, motion, one_finger_drag, primary_tap, secondary_tap},
     crate::{input_device, input_handler::UnhandledInputHandler, mouse_binding, touch_binding},
     anyhow::{format_err, Error},
     async_trait::async_trait,
@@ -34,6 +34,9 @@ pub fn make_input_handler() -> std::rc::Rc<dyn crate::input_handler::InputHandle
                 max_finger_displacement_in_mm: MAX_TAP_MOVEMENT_IN_MM,
                 max_time_elapsed: TAP_TIMEOUT,
             }),
+            Box::new(one_finger_drag::InitialContender {
+                min_movement_in_mm: SPURIOUS_TO_INTENTIONAL_MOTION_THRESHOLD_MM,
+            }),
         ]
     }))
 }

src/ui/lib/input_pipeline/src/gestures/one_finger_drag.rs

@@ -19,9 +19,9 @@ use {
 
 /// The initial state of this recognizer, before a finger contact has been detected.
 #[derive(Debug)]
-struct Contender {
+pub(super) struct InitialContender {
     /// The minimum movement in millimeters on surface to recognize as a motion.
-    min_movement_in_mm: f32,
+    pub(super) min_movement_in_mm: f32,
 }
 
 /// The state when this recognizer has detected a finger pressed buttondown, before finger
@@ -47,7 +47,7 @@ struct Winner {
     last_position: Position,
 }
 
-impl Contender {
+impl InitialContender {
     fn into_button_down_contender(
         self: Box<Self>,
         initial_position: Position,
@@ -59,7 +59,7 @@ impl Contender {
     }
 }
 
-impl gesture_arena::Contender for Contender {
+impl gesture_arena::Contender for InitialContender {
     fn examine_event(self: Box<Self>, event: &TouchpadEvent) -> ExamineEventResult {
         if event.contacts.len() != 1 {
             return ExamineEventResult::Mismatch("wanted 1 contact");
@@ -286,7 +286,7 @@ mod test {
     #[fuchsia::test]
     fn initial_contender_examine_event_mismatch(event: TouchpadEvent) {
         let contender: Box<dyn gesture_arena::Contender> =
-            Box::new(Contender { min_movement_in_mm: 10.0 });
+            Box::new(InitialContender { min_movement_in_mm: 10.0 });
 
         let got = contender.examine_event(&event);
         assert_matches!(got, ExamineEventResult::Mismatch(_));
@@ -295,7 +295,7 @@ mod test {
     #[fuchsia::test]
     fn initial_contender_examine_event_button_down_contender() {
         let contender: Box<dyn gesture_arena::Contender> =
-            Box::new(Contender { min_movement_in_mm: 10.0 });
+            Box::new(InitialContender { min_movement_in_mm: 10.0 });
         let event = TouchpadEvent {
             timestamp: zx::Time::ZERO,
             pressed_buttons: vec![1],