Made Wavepool mode smaller in ROM. (about 300 bytes smaller)

Most of this came from replacing rand().
The rest mostly came from smaller height field calculation logic.
Also some other small changes which don't seem to make much difference visually.

src/Kaleidoscope/LED-Wavepool.cpp

@@ -21,6 +21,8 @@
 
 namespace kaleidoscope {
 
+#define MS_PER_FRAME_POW2 6  // one frame every 64 ms
+
 int8_t WavepoolEffect::surface[2][WP_WID*WP_HGT];
 uint8_t WavepoolEffect::page = 0;
 uint8_t WavepoolEffect::frames_since_event = 0;
@@ -74,11 +76,19 @@ void WavepoolEffect::raindrop(uint8_t x, uint8_t y, int8_t *page) {
   if (x < (WP_WID-1)) page[rainspot+1] = 0x60;
 }
 
+// this is a lot smaller than the standard library's rand(),
+// and still looks random-ish
+uint8_t WavepoolEffect::wp_rand() {
+    static uint16_t offset = 0x400;
+    offset = ((offset + 1) & 0x4fff) | 0x400;
+    return (millis()>>MS_PER_FRAME_POW2) + pgm_read_byte(offset);
+}
+
 void WavepoolEffect::update(void) {
 
   // limit the frame rate; one frame every 64 ms
   static uint8_t prev_time = 0;
-  uint8_t now = (millis()>>6) % 0xff;
+  uint8_t now = (millis()>>MS_PER_FRAME_POW2) % 0xff;
   if (now != prev_time) {
       prev_time = now;
   } else {
@@ -88,9 +98,6 @@ void WavepoolEffect::update(void) {
   // rotate the colors over time
   // (side note: it's weird that this is a 16-bit int instead of 8-bit,
   //  but that's what the library function wants)
-  //static uint16_t current_hue = 0;
-  //current_hue ++;
-  //current_hue &= 0xff;
   static uint8_t current_hue = 0;
   current_hue ++;
 
@@ -110,12 +117,14 @@ void WavepoolEffect::update(void) {
       raindrop(prev_x, prev_y, oldpg);
       prev_x = prev_y = -1;
     }
-    if (frames_since_event >= (frames_till_next_drop + (idle_timeout >> 6))) {
-        frames_till_next_drop = 4 + (rand() & 0x3f);
-        frames_since_event = idle_timeout >> 6;
+    if (frames_since_event
+            >= (frames_till_next_drop
+                + (idle_timeout >> MS_PER_FRAME_POW2))) {
+        frames_till_next_drop = 4 + (wp_rand() & 0x3f);
+        frames_since_event = idle_timeout >> MS_PER_FRAME_POW2;
 
-        uint8_t x = rand() % WP_WID;
-        uint8_t y = rand() % WP_HGT;
+        uint8_t x = wp_rand() % WP_WID;
+        uint8_t y = wp_rand() % WP_HGT;
         raindrop(x, y, oldpg);
 
         prev_x = x;
@@ -159,17 +168,13 @@ void WavepoolEffect::update(void) {
           offsets[7] -= 1;
           }
 
-      value = ((oldpg[offset + offsets[0]]
-               +oldpg[offset + offsets[1]]
-               +oldpg[offset + offsets[2]]
-               +oldpg[offset + offsets[3]]
-               +oldpg[offset + offsets[4]]
-               +oldpg[offset + offsets[5]]
-               +oldpg[offset + offsets[6]]
-               +oldpg[offset + offsets[7]]
-               ) >> 2)
-               - newpg[offset];
+      // add up all samples, divide, subtract prev frame's center
+      int8_t *p;
+      for(p=offsets, value=0; p<offsets+8; p++)
+          value += oldpg[offset + (*p)];
+      value = (value >> 2) - newpg[offset];
 
+      // reduce intensity gradually over time
       newpg[offset] = value - (value >> 3);
     }
   }
@@ -178,22 +183,17 @@ void WavepoolEffect::update(void) {
   for (byte r = 0; r < ROWS; r++) {
     for (byte c = 0; c < COLS; c++) {
       uint8_t offset = (r*COLS) + c;
-      int8_t value = oldpg[pgm_read_byte(rc2pos+offset)];
+      int8_t height = oldpg[pgm_read_byte(rc2pos+offset)];
 
-      uint16_t intensity;
-      intensity = abs(value) * 2;
-      if (intensity > 254) intensity = 254;
+      uint8_t intensity = abs(height) * 2;
 
       // color starts white but gets dimmer and more saturated as it fades,
       // with hue wobbling according to height map
-      int16_t hue = current_hue;
-      hue = hue + value + (value>>1);
-      hue = hue & 0xff;
+      int16_t hue = (current_hue + height + (height>>1)) & 0xff;
 
-      cRGB color;
-      color = hsvToRgb(hue,
+      cRGB color = hsvToRgb(hue,
                             0xff - intensity,
-                       intensity*2);
+                            ((uint16_t)intensity)*2);
 
       LEDControl.setCrgbAt(r, c, color);
     }

src/Kaleidoscope/LED-Wavepool.h

@@ -44,6 +44,7 @@ class WavepoolEffect : public LEDMode {
 
   static Key eventHandlerHook(Key mapped_key, byte row, byte col, uint8_t key_state);
   static void raindrop(uint8_t x, uint8_t y, int8_t *page);
+  static uint8_t wp_rand();
 };
 
 }