Address #1689 by using a formula to define the breathing curve (#1692)

* Address #1689 by using a formula to define the breathing curve and exposing defines to control the shape of the curve.

* Tweak the behavior of breathing for clueboard

docs/feature_rgblight.md

@@ -49,8 +49,10 @@ If you have `#define RGBLIGHT_ANIMATIONS` in your `config.h` you will have a num
 | Option | Default Value | Description |
 |--------|---------------|-------------|
 | `RGBLIGHT_ANIMATIONS` | | `#define` this to enable animation modes. |
-| `RGBLIGHT_EFFECT_SNAKE_LENGTH` | 4 | The number of LEDs to light up for the "snake" mode. |
-| `RGBLIGHT_EFFECT_KNIGHT_LENGTH` | 3 | The number of LEDs to light up for the "knight" mode. |
+| `RGBLIGHT_EFFECT_BREATHE_CENTER | 1.85 | Used to calculate the curve for the breathing animation. Valid values 1.0-2.7. |
+| `RGBLIGHT_EFFECT_BREATHE_MAX | 255 | The maximum brightness for the breathing mode. Valid values 1-255. |
+| `RGBLIGHT_EFFECT_SNAKE_LENGTH` | 4 | The number of LEDs to light up for the "snake" animation. |
+| `RGBLIGHT_EFFECT_KNIGHT_LENGTH` | 3 | The number of LEDs to light up for the "knight" animation. |
 | `RGBLIGHT_EFFECT_KNIGHT_OFFSET` | 0 | Start the knight animation this many LEDs from the start of the strip. |
 | `RGBLIGHT_EFFECT_KNIGHT_LED_NUM` | RGBLED_NUM | The number of LEDs to have the "knight" animation travel. |
 | `RGBLIGHT_EFFECT_CHRISTMAS_INTERVAL` | 1000 | How long to wait between light changes for the "christmas" animation. Specified in ms. |

keyboards/clueboard_66/rev2/config.h

@@ -36,6 +36,8 @@
 #define RGBLIGHT_VAL_STEP 17
 
 #define RGBLIGHT_ANIMATIONS
+#define RGBLIGHT_EFFECT_BREATHE_CENTER 1
+#define RGBLIGHT_EFFECT_BREATHE_MAX 200
 #define RGBLIGHT_EFFECT_CHRISTMAS_INTERVAL 666*2
 #define RGBLIGHT_EFFECT_CHRISTMAS_STEP 1
 #define RGBLIGHT_EFFECT_KNIGHT_LENGTH 3   // How many LEDs wide to light up

keyboards/clueboard_66/rev3/config.h

@@ -36,6 +36,8 @@
 #define RGBLIGHT_VAL_STEP 17
 
 #define RGBLIGHT_ANIMATIONS
+#define RGBLIGHT_EFFECT_BREATHE_CENTER 1
+#define RGBLIGHT_EFFECT_BREATHE_MAX 200
 #define RGBLIGHT_EFFECT_CHRISTMAS_INTERVAL 666*2
 #define RGBLIGHT_EFFECT_CHRISTMAS_STEP 1
 #define RGBLIGHT_EFFECT_KNIGHT_LENGTH 3   // How many LEDs wide to light up

quantum/rgblight.c

@@ -13,6 +13,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
+#include <math.h>
 #include <avr/eeprom.h>
 #include <avr/interrupt.h>
 #include <util/delay.h>
@@ -465,13 +466,17 @@ void rgblight_task(void) {
 void rgblight_effect_breathing(uint8_t interval) {
   static uint8_t pos = 0;
   static uint16_t last_timer = 0;
+  float val;
 
   if (timer_elapsed(last_timer) < pgm_read_byte(&RGBLED_BREATHING_INTERVALS[interval])) {
     return;
   }
   last_timer = timer_read();
 
-  rgblight_sethsv_noeeprom(rgblight_config.hue, rgblight_config.sat, pgm_read_byte(&LED_BREATHING_TABLE[pos]));
+
+  // http://sean.voisen.org/blog/2011/10/breathing-led-with-arduino/
+  val = (exp(sin((pos/255.0)*M_PI)) - RGBLIGHT_EFFECT_BREATHE_CENTER/M_E)*(RGBLIGHT_EFFECT_BREATHE_MAX/(M_E-1/M_E));
+  rgblight_sethsv_noeeprom(rgblight_config.hue, rgblight_config.sat, val);
   pos = (pos + 1) % 256;
 }
 void rgblight_effect_rainbow_mood(uint8_t interval) {

quantum/rgblight.h

@@ -22,6 +22,14 @@
 	#define RGBLIGHT_MODES 1
 #endif
 
+#ifndef RGBLIGHT_EFFECT_BREATHE_CENTER
+#define RGBLIGHT_EFFECT_BREATHE_CENTER 1.85  // 1-2.7
+#endif
+
+#ifndef RGBLIGHT_EFFECT_BREATHE_MAX
+#define RGBLIGHT_EFFECT_BREATHE_MAX 255   // 0-255
+#endif
+
 #ifndef RGBLIGHT_EFFECT_SNAKE_LENGTH
 #define RGBLIGHT_EFFECT_SNAKE_LENGTH 4
 #endif