Remove display flash every interval

Add variable to remember previous value of hidx, and check to see if it has changed before we redraw the watchface

apps/impwclock/clock-impword.js

@@ -46,6 +46,8 @@ const passivColor = 0x3186 /*grey*/ ;
 const activeColorNight = 0xF800 /*red*/ ;
 const activeColorDay = 0xFFFF /* white */;
 
+var hidxPrev;
+
 function drawWordClock() {
 
 
@@ -65,19 +67,6 @@ function drawWordClock() {
     g.setColor(passivColor);
     g.setFontAlign(0, -1, 0);
 
-    // draw allWords
-    var c;
-    var y = ys;
-    var x = xs;
-    allWords.forEach((line) => {
-        x = xs;
-        for (c in line) {
-            g.drawString(line[c], x, y);
-            x += dx;
-        }
-        y += dy;
-    });
-
 
     // Switch case isn't good for this in Js apparently so...
     if(h < 3){
@@ -125,6 +114,21 @@ function drawWordClock() {
     hidx = 10;
     }
 
+    // check whether we need to redraw the watchface
+    if (hidx !== hidxPrev) {
+      // draw allWords
+      var c;
+      var y = ys;
+      var x = xs;
+      allWords.forEach((line) => {
+          x = xs;
+          for (c in line) {
+              g.drawString(line[c], x, y);
+              x += dx;
+          }
+          y += dy;
+      });
+
       // write hour in active color
       g.setColor(activeColor);
       timeOfDay[hidx][0].split('').forEach((c, pos) => {
@@ -132,16 +136,17 @@ function drawWordClock() {
           y = ys + (timeOfDay[hidx][pos + 1] % 10) * dy;
           g.drawString(c, x, y);
       });
-
+      hidxPrev = hidx;
+    }
 
     // Display digital time while button 1 is pressed
+    g.clearRect(0, 215, 240, 240);
     if (BTN1.read()){
         g.setColor(activeColor);
-        g.clearRect(0, 215, 240, 240);
         g.drawString(time, 120, 215);
-    } else { g.clearRect(0, 215, 240, 240); }
-    
     }
+}
+
 
 Bangle.on('lcdPower', function(on) {
   if (on) drawWordClock();