Added a function to allow a user to set a gamma correction factor.

This will generate and apply this correction table to the led gamma setting.

Author: Robert Winslow

SConstruct

@@ -48,6 +48,7 @@ platforms = [
             ],
             'LINKFLAGS' : [
                 "-lrt",
+		"-lm",
             ],
         },
     ], 

ws2811.c

@@ -41,7 +41,7 @@
 #include <linux/types.h>
 #include <linux/spi/spidev.h>
 #include <time.h>
-
+#include <math.h>
 #include "mailbox.h"
 #include "clk.h"
 #include "gpio.h"
@@ -1282,3 +1282,23 @@ const char * ws2811_get_return_t_str(const ws2811_return_t state)
 
     return "";
 }
+
+
+void setCustomGammaFactor(ws2811_t *ws2811, double gammaFactor)
+{
+    for (int chan = 0; chan < RPI_PWM_CHANNELS; chan++)
+    {
+        ws2811_channel_t *channel = &ws2811->channel[chan];
+
+        if (channel->gamma)
+        {
+          for(int counter = 0; counter < 256; counter++)
+          {
+
+             channel->gamma[counter] = (gammaFactor > 0)? (int)(pow((float)counter / (float)255.00, gammaFactor) * 255.00 + 0.5) : counter;
+
+          }
+        }
+
+    }
+}

ws2811.h

@@ -122,6 +122,7 @@ void ws2811_fini(ws2811_t *ws2811);                                    //< Tear
 ws2811_return_t ws2811_render(ws2811_t *ws2811);                       //< Send LEDs off to hardware
 ws2811_return_t ws2811_wait(ws2811_t *ws2811);                         //< Wait for DMA completion
 const char * ws2811_get_return_t_str(const ws2811_return_t state);     //< Get string representation of the given return state
+void setCustomGammaFactor(ws2811_t *ws2811, double gammaFactor); //Set a custom Gamma correction array based on a gamma correction factor
 
 #ifdef __cplusplus
 }