From 3914df55902fd661761a2da773046612b32373e8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?King=20K=C3=A9vin?= <kingkevin@cuvoodoo.info>
Date: Mon, 28 Mar 2016 16:39:11 +0200
Subject: [PATCH] add gamma correction

---
 main.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/main.c b/main.c
index 9398c91..12c046d 100644
--- a/main.c
+++ b/main.c
@@ -28,6 +28,7 @@
 #include <unistd.h> // standard streams
 #include <errno.h> // error number utilities
 #include <string.h> // string utilities
+#include <math.h> // mathematical utilities
 
 /* STM32 (including CM3) libraries */
 #include <libopencm3/stm32/rcc.h> // real-time control clock library
@@ -92,6 +93,8 @@ volatile uint32_t current_time = 0;
 char command[32] = {0};
 /** user input command index */
 uint8_t command_i = 0;
+/** gamma correction lookup table (common for all colors) */
+uint8_t gamma_correction_lut[256] = {0};
 
 int _write(int file, char *ptr, int len)
 {
@@ -248,7 +251,7 @@ static void clock_leds_set(void)
 			clock_leds_old[i*3+0] = clock_leds[i*3+0]; // memorise change
 			clock_leds_old[i*3+1] = clock_leds[i*3+1]; // memorise change
 			clock_leds_old[i*3+2] = clock_leds[i*3+2]; // memorise change
-			ws2812b_set_rgb(i,clock_leds[i*3+0],clock_leds[i*3+1],clock_leds[i*3+2]); // set new value (this costs time)
+			ws2812b_set_rgb(i,gamma_correction_lut[clock_leds[i*3+0]],gamma_correction_lut[clock_leds[i*3+1]],gamma_correction_lut[clock_leds[i*3+2]]); // set new value (this costs time)
 		}
 	}
 }
@@ -378,6 +381,11 @@ int main(void)
 	nvic_enable_irq(BUTTON_IRQ); // enable interrupt
 #endif
 
+	// generate gamma correction table (with fixed gamma value)
+	for (uint16_t i=0; i<LENGTH(gamma_correction_lut); i++) {
+		gamma_correction_lut[i] = powf((float)i / (float)LENGTH(gamma_correction_lut), 2.5)*LENGTH(gamma_correction_lut);
+	}
+
 	// setup WS2812b LEDs
 	ws2812b_setup(); // setup WS2812b LEDs
 	clock_hours(); // show hour markers
@@ -494,6 +502,7 @@ void BUTTON_ISR(void)
 #endif
 
 #if defined(SQUARE_WAVE_TIMER_IRQ) && defined(SQUARE_WAVE_TIMER_ISR)
+/** @brief timer interrupt when square wave output accumulated to a tick */
 void SQUARE_WAVE_TIMER_ISR(void)
 {
 	if (timer_get_flag(SQUARE_WAVE_TIMER, TIM_SR_UIF)) { // overflow even happened