Improved timer handling

Instead of calculating the elapsed time every time we check the timer,
calculate the projected end-time when we start the timer, and just
compare millis() against that.

Also removes the `.configure()` method, in favour of making the
`timeOut` property public.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>

README.md

@@ -39,21 +39,23 @@ is highly recommended.
 
 The plugin provides two methods on the `HeatmapEffect` object:
 
-### `.configure(updateFrequency)`
-
-> Sets up the update frequency of the heatmap, to update every `updateFrequency`
-> milliseconds. Updating the heatmap incurs a significant performance penalty,
-> and should not be done too often. Doing it too rarely, on the other hand, make
-> it much less useful. One has to strike a reasonable balance.
->
-> Defaults to *500*.
-
 ### `.activate()`
 
 > When called, immediately activates the Heatmap effect. Mostly useful in the
 > `setup()` method of the Sketch, or in macros that are meant to switch to the
 > heatmap effect, no matter where we are in the list.
 
+### `.timeOut`
+
+> The number of milliseconds to wait between updating the heatmap. Updating the
+> heatmap incurs a significant performance penalty, and should not be done too
+> often. Doing it too rarely, on the other hand, make it much less useful. One
+> has to strike a reasonable balance.
+>
+> Not strictly a method, it is a variable one can assign a new value to.
+>
+> Defaults to *500*.
+
 ## Further reading
 
 Starting from the [example][plugin:example] is the recommended way of getting

src/Kaleidoscope/Heatmap.cpp

@@ -23,8 +23,8 @@ namespace KaleidoscopePlugins {
   uint8_t Heatmap::heatmap[ROWS][COLS];
   uint16_t Heatmap::totalKeys;
   uint8_t Heatmap::highestCount;
-  uint16_t Heatmap::updateFrequency = 500;
+  uint16_t Heatmap::updateDelay = 500;
-  uint32_t Heatmap::startTime;
+  uint32_t Heatmap::endTime;
 
   const float Heatmap::heatColors[][3] = {{0.0, 0.0, 0.0}, {0.1, 1, 0.1}, {1, 1, 0.1}, {1, 0.1, 0.1}};
 
@@ -74,11 +74,6 @@ namespace KaleidoscopePlugins {
     loop_hook_use (this->loopHook);
   }
 
-  void
-  Heatmap::configure (uint16_t updateFreq) {
-    updateFrequency = updateFreq;
-  }
-
   Key
   Heatmap::eventHook (Key mappedKey, byte row, byte col, uint8_t keyState) {
     // if it is a synthetic key, skip it.
@@ -105,10 +100,10 @@ namespace KaleidoscopePlugins {
 
   void
   Heatmap::update (void) {
-    if (startTime && (millis () - startTime) < updateFrequency)
+    if (endTime && (millis () > endTime))
       return;
 
-    startTime = millis ();
+    endTime = millis () + updateDelay;
 
     for (uint8_t r = 0; r < ROWS; r++) {
       for (uint8_t c = 0; c < COLS; c++) {

src/Kaleidoscope/Heatmap.h

@@ -28,15 +28,14 @@ namespace KaleidoscopePlugins {
 
     virtual void begin (void) final;
 
-    static void configure (uint16_t updateFrequency);
+    static uint16_t updateDelay;
 
     virtual void update (void) final;
   private:
     static uint8_t heatmap[ROWS][COLS];
     static uint16_t totalKeys;
     static uint8_t highestCount;
-    static uint16_t updateFrequency;
+    static uint32_t endTime;
-    static uint32_t startTime;
 
     static const float heatColors[][3];