From 138af7a4919661814184dc6ec4fb6c4070e3e1da Mon Sep 17 00:00:00 2001
From: Eric Rosenbaum <eric.rosenbaum@gmail.com>
Date: Mon, 25 Mar 2019 15:15:45 -0400
Subject: [PATCH] Stabilize facing up and facing down

---
 src/extensions/scratch3_gdx_for/index.js | 39 ++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/src/extensions/scratch3_gdx_for/index.js b/src/extensions/scratch3_gdx_for/index.js
index 9d5f77619..e201a7907 100644
--- a/src/extensions/scratch3_gdx_for/index.js
+++ b/src/extensions/scratch3_gdx_for/index.js
@@ -80,6 +80,12 @@ const SHAKEN_THRESHOLD = 30;
  */
 const FACING_THRESHOLD = 9;
 
+/**
+ * An offset for the facing threshold, used to check that we are no longer facing up.
+ * @type {number}
+ */
+const FACING_THRESHOLD_OFFSET = 5;
+
 /**
  * Threshold for acceleration magnitude, below which we are in freefall.
  * @type {number}
@@ -783,15 +789,44 @@ class Scratch3GdxForBlocks {
         case GestureValues.STARTED_FALLING:
             return this.isFreeFalling();
         case GestureValues.TURNED_FACE_UP:
-            return this._peripheral.getAccelerationZ() > FACING_THRESHOLD;
+            return this._isFacing(GestureValues.TURNED_FACE_UP);
         case GestureValues.TURNED_FACE_DOWN:
-            return this._peripheral.getAccelerationZ() < FACING_THRESHOLD * -1;
+            return this._isFacing(GestureValues.TURNED_FACE_DOWN);
         default:
             log.warn(`unknown gesture value in whenGesture: ${args.GESTURE}`);
             return false;
         }
     }
 
+    _isFacing (direction) {
+        if (typeof this._facingUp === 'undefined') {
+            this._facingUp = false;
+        }
+        if (typeof this._facingDown === 'undefined') {
+            this._facingDown = false;
+        }
+
+        // If the sensor is already facing up or down, reduce the threshold.
+        // This prevents small fluctations in acceleration while it is being
+        // turned from causing the hat block to trigger multiple times.
+        let threshold = FACING_THRESHOLD;
+        if (this._facingUp || this._facingDown) {
+            threshold -= FACING_THRESHOLD_OFFSET;
+        }
+
+        this._facingUp = this._peripheral.getAccelerationZ() > threshold;
+        this._facingDown = this._peripheral.getAccelerationZ() < threshold * -1;
+
+        switch (direction) {
+        case GestureValues.TURNED_FACE_UP:
+            return this._facingUp;
+        case GestureValues.TURNED_FACE_DOWN:
+            return this._facingDown;
+        default:
+            return false;
+        }
+    }
+
     whenTilted (args) {
         return this._isTilted(args.TILT);
     }