Add dithering

include/picoled.h

@@ -2,26 +2,25 @@
 #define PICOLED_H
 
 #include <cstddef>
+#include <cstdint>
 
 namespace picoled
 {
 
 class pixel
 {
+  friend class oled;
 public:
   pixel() :
-    pixel(false)
+    pixel(0)
   {}
 
-  pixel(bool on) :
+  pixel(uint8_t value) :
-    on(on)
+    value(value)
   {}
 
-  bool is_on() const { return on; }
-  void invert() { on = !on; }
-
 private:
-  bool on;
+  uint8_t value;
 };
 
 class oled
@@ -44,9 +43,13 @@ public:
   size_t get_width() const { return width; }
   size_t get_height() const { return height; }
 
-  virtual void update() const = 0;
+  void update() const;
 
 protected:
+  virtual void update_impl() const = 0;
+
+  bool is_on(int x, int y) const;
+
   size_t width;
   size_t height;
 

include/picoled/SSD1306.h

@@ -16,7 +16,8 @@ public:
   ssd1306(i2c_inst* i2c, uint8_t address);
   virtual ~ssd1306();
 
-  void update() const override;
+protected:
+  void update_impl() const override;
 
 private:
   void command(uint8_t cmd) const;

src/SSD1306.cpp

@@ -77,7 +77,7 @@ ssd1306::~ssd1306()
   delete[] buffer;
 }
 
-void ssd1306::update() const
+void ssd1306::update_impl() const
 {
   // clear display to zero
   memset(&buffer[1], 0, width * height * sizeof(*buffer));
@@ -86,7 +86,7 @@ void ssd1306::update() const
   {
     for (int y = 0; y < height; y++)
     {
-      if (!(*this)(x, y).is_on()) { continue; }
+      if (!is_on(x, y)) { continue; }
 
       const int index = (width - x - 1) + (y / 8) * width;
       const uint8_t bits = 1 << (y & 7);

src/picoled.cpp

@@ -1,5 +1,14 @@
 #include "picoled.h"
 
+#include <cstdlib>
+
+namespace
+{
+
+picoled::pixel DUMMY_PIXEL;
+
+}
+
 namespace picoled
 {
 
@@ -14,18 +23,29 @@ oled::~oled()
   delete[] pixels;
 }
 
+
 pixel& oled::operator()(int x, int y)
 {
-  static pixel dummy;
+  if (x < 0 || x >= width || y < 0 || y >= height) { return DUMMY_PIXEL; }
-  if (x < 0 || x >= width || y < 0 || y >= height) { return dummy; }
   return pixels[x + y * width];
 }
 
 const pixel& oled::operator()(int x, int y) const
 {
+  if (x < 0 || x >= width || y < 0 || y >= height) { return DUMMY_PIXEL; }
   return pixels[x + y * width];
 }
 
+void oled::update() const
+{
+  update_impl();
+}
+
+bool oled::is_on(int x, int y) const
+{
+  return (*this)(x, y).value > rand() % 0xFF;
+}
+
 void oled::clear()
 {
   for (int i = 0; i < width * height; i++)