Dial: new module providing a circular dial

Only the drag gesture functionality provided. I intend to add a
companion module providing some relevant graphics, sharing the same
options object.

Author: thyttan

apps/modules/Dial.js

@@ -0,0 +1,89 @@
+let Dial = function(cb, options) {
+    "ram";
+    const SCREEN_W = g.getWidth();
+    const SCREEN_H = g.getHeight();
+
+    options = Object.assign(
+      { stepsPerWholeTurn : 8,
+        dialRect : {
+          x: 0,
+          y: 0,
+          x2: SCREEN_W - 1,
+          y2: SCREEN_H - 1,
+          w: SCREEN_W,
+          h: SCREEN_H,
+        },
+      }, options);
+
+    const DIAL_RECT = options.dialRect;
+
+    const CENTER = {
+      x: DIAL_RECT.x + DIAL_RECT.w / 2,
+      y: DIAL_RECT.y + DIAL_RECT.h / 2,
+    };
+
+    const BASE_SCREEN_W = 176;
+    const STEPS_PER_TURN = options.stepsPerWholeTurn;
+    const BASE_THRESHOLD = 50;
+    const THRESHOLD =
+      BASE_THRESHOLD *
+      (10 / STEPS_PER_TURN) *
+      (DIAL_RECT.w / BASE_SCREEN_W);
+
+    let cumulative = 0;
+
+    function onDrag(e) {
+      "ram";
+
+      if (
+        e.x < DIAL_RECT.x ||
+        e.x > DIAL_RECT.x2 ||
+        e.y < DIAL_RECT.y ||
+        e.y > DIAL_RECT.y2
+      ) {
+        return;
+      }
+
+      if (e.y < CENTER.y) {
+        cumulative += e.dx;
+      } else {
+        cumulative -= e.dx;
+      }
+
+      if (e.x < CENTER.x) {
+        cumulative -= e.dy;
+      } else {
+        cumulative += e.dy;
+      }
+
+      function stepHandler(step) {
+        cumulative -= THRESHOLD * step;
+        cb(step);
+      }
+
+      while (cumulative > THRESHOLD) {
+        stepHandler(1);
+      }
+      while (cumulative < -THRESHOLD) {
+        stepHandler(-1);
+      }
+
+      E.stopEventPropagation();
+    }
+
+    return onDrag;
+/*
+    if (exports.dial._handler) {
+      Bangle.removeListener("drag", dial._handler);
+    }
+
+    exports.dial._handler = onDrag;
+    Bangle.prependListener("drag", onDrag);
+    
+    Bangle.prependListener("swipe", ()=>{ 
+      E.stopEventPropagation();
+    }
+                          );*/
+  };
+
+exports = Dial;