Add backlight implementation

Author: facchinm

examples/backlight/SimpleBacklight/SimpleBacklight.ino

@@ -0,0 +1,20 @@
+/*
+  Changes the display backlight from very dim to 100%
+  This example code is in the public domain.
+*/
+
+#include <Arduino_GigaDisplay.h>
+
+//Create backlight object
+GigaDisplayBacklight backlight;
+
+void setup() {
+  //init library
+  backlight.begin();
+}
+
+int i = 0;
+void loop() {
+  backlight.set(i++ % 100);
+  delay(100);
+}

src/GigaDisplayRGB.h

@@ -13,4 +13,41 @@ class GigaDisplayRGB {
         void writeByte(uint8_t,uint8_t);
 };
 
+#include "mbed.h"
+using namespace std::chrono_literals;
+using namespace std::chrono;
+
+class GigaDisplayBacklight {
+    public:
+        GigaDisplayBacklight() {}
+        void begin(int target_percent = 100) {
+            pin = new mbed::DigitalOut(PB_12);
+            ticker = new mbed::Ticker();
+            ticker->attach(mbed::callback(this, &GigaDisplayBacklight::cb), 2ms);
+            set(target_percent);
+        }
+        void cb() {
+            static int counter = 0;
+            if (counter > intensity) {
+                *pin = 0;
+            } else {
+                *pin = 1;
+            }
+            counter += 10;
+            if (counter == 100) {
+                counter = 0;
+            }
+        }
+        void set(int target_percent) {
+            intensity = target_percent;
+        }
+        void off() {
+            set(0);
+        }
+    private:
+        mbed::Ticker* ticker;
+        mbed::DigitalOut* pin;
+        int intensity;
+};
+
 #endif