Add platformio demo (#153)

examples/platformio/.gitignore

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+.pio
+.vscode/.browse.c_cpp.db*
+.vscode/c_cpp_properties.json
+.vscode/launch.json
+.vscode/ipch
+.vscode/settings.json
+lib/etl

examples/platformio/.vscode/extensions.json

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+{
+	// See http://go.microsoft.com/fwlink/?LinkId=827846
+	// for the documentation about the extensions.json format
+	"recommendations": [
+		"platformio.platformio-ide"
+	]
+}

examples/platformio/README.md

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+ETL PlatformIO demo
+===================
+
+> Template to demonstrate how to use ETL with PlatformIO.
+
+1. Open this folder in VSCode and agree if it suggests to install extension.
+2. Use `Terminal -> Run Build Task... -> PlatformIO: Build` menu to compile.
+3. Run `.pio/Build/native/program`.
+
+## Details
+
+Use `platformio.ini` for example, see comments inside.
+
+`include` folder contains config, required for `etl`. All is as transparent
+as possible. Set all additional variables via `build_flags` option in
+`platform.ini`. Currently only `PROFILE_GCC_GENERIC` set to make things work.

examples/platformio/include/etl_profile.h

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+#include "etl/profiles/etl_profile.h"

examples/platformio/platformio.ini

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+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; http://docs.platformio.org/page/projectconf.html
+
+[platformio]
+default_envs = native
+
+[env:native]
+platform = native
+build_flags =
+  ; ETL configs in `include` folder are minimalistic. Here we can set all
+  ; additional definitions to keep everything in one place and customize values
+  ; for different target platforms
+  -D PROFILE_GCC_GENERIC
+lib_deps =
+  ; Define ETL dependency for this demo. You can use versions from PIO registry,
+  ; or git repository with specific branch, tag or commit. See PIO docs for
+  ; details.
+  ;Embedded Template Library=https://github.com/ETLCPP/etl/archive/master.zip
+  Embedded Template Library@^14.31.2
+

examples/platformio/src/main.cpp

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+#include <iostream>
+
+#include "etl/observer.h"
+
+// Position data.
+struct Position
+{
+  int x;
+  int y;
+};
+
+// Button data.
+struct Button
+{
+  enum
+  {
+    Down,
+    Up
+  };
+
+  int state;
+};
+
+// Wheel data.
+struct Wheel
+{
+  int delta;
+};
+
+// Definition of a mouse observer.
+typedef etl::observer<const Position&, Button, Wheel> Mouse_Observer;
+
+// Definition of an event handler for mouse notifications.
+class Event_Handler1 : public Mouse_Observer
+{
+public:
+
+  // Handle a position notification.
+  void notification(const Position& position)
+  {
+    std::cout << "Event_Handler1 : Position = " << position.x << "," << position.y << "\n";
+  }
+
+  // Handle a button notification.
+  void notification(Button button)
+  {
+    std::cout << "Event_Handler1 : Button = " << ((button.state == Button::Up) ? "Up\n" : "Down\n");
+  }
+
+  // Handle a wheel notification.
+  void notification(Wheel wheel)
+  {
+    std::cout << "Event_Handler1 : Wheel delta = " << wheel.delta << "\n";
+  }
+};
+
+// Definition of a second event handler for mouse notifications.
+class Event_Handler2 : public Mouse_Observer
+{
+public:
+
+  // Handler a position notification.
+  void notification(const Position& position)
+  {
+    std::cout << "Event_Handler2 : Position = " << position.x << "," << position.y << "\n";
+  }
+
+  // Handle a button notification.
+  void notification(Button button)
+  {
+    std::cout << "Event_Handler2 : Button = " << ((button.state == Button::Up) ? "Up\n" : "Down\n");
+  }
+
+  // Handle a wheel notification.
+  void notification(Wheel wheel)
+  {
+    // Not interested in wheel deltas.
+  }
+};
+
+// The observable mouse driver.
+const int MAX_MOUSE_OBSERVERS = 2;
+
+class Mouse_Driver : public etl::observable<Mouse_Observer, MAX_MOUSE_OBSERVERS>
+{
+public:
+
+  // Notify observers about a position event.
+  void Position_Event()
+  {
+    Position position = { 100, 200 };
+    notify_observers(position);
+  }
+
+  // Notify observers about a button up event.
+  void Button_Event_Up()
+  {
+    Button button = { Button::Up };
+    notify_observers(button);
+  }
+
+  // Notify observers about a button down event.
+  void Button_Event_Down()
+  {
+    Button button = { Button::Down };
+    notify_observers(button);
+  }
+
+  // Notify observers about a wheel up event.
+  void Wheel_Event_Up()
+  {
+    Wheel wheel = { 50 };
+    notify_observers(wheel);
+  }
+
+  // Notify observers about a wheel down event.
+  void Wheel_Event_Down()
+  {
+    Wheel wheel = { -25 };
+    notify_observers(wheel);
+  }
+};
+
+int main()
+{
+  Mouse_Driver   mouse_driver;
+  Event_Handler1 event_handler1;
+  Event_Handler2 event_handler2;
+
+  // Tell the mouse driver about the observers.
+  mouse_driver.add_observer(event_handler1);
+  mouse_driver.add_observer(event_handler2);
+
+  // Generate some events.
+  mouse_driver.Button_Event_Down();
+  mouse_driver.Button_Event_Up();
+  mouse_driver.Position_Event();
+  mouse_driver.Wheel_Event_Down();
+  mouse_driver.Wheel_Event_Up();
+
+  return 0;
+}