rpi-rgb-led-matrix/examples-api-use/minimal-example.cc

// -*- mode: c++; c-basic-offset: 2; indent-tabs-mode: nil; -*-
// Small example how to use the library.
// For more examples, look at demo-main.cc
//
// This code is public domain
// (but note, that the led-matrix library this depends on is GPL v2)

#include "led-matrix.h"

#include <unistd.h>
#include <math.h>
#include <stdio.h>

using rgb_matrix::GPIO;
using rgb_matrix::RGBMatrix;
using rgb_matrix::Canvas;

static void DrawOnCanvas(Canvas *canvas) {
  /*
   * Let's create a simple animation. We use the canvas to draw
   * pixels. We wait between each step to have a slower animation.
   */
  canvas->Fill(0, 0, 255);

  int center_x = canvas->width() / 2;
  int center_y = canvas->height() / 2;
  float radius_max = canvas->width() / 2;
  float angle_step = 1.0 / 360;
  for (float a = 0, r = 0; r < radius_max; a += angle_step, r += angle_step) {
    float dot_x = cos(a * 2 * M_PI) * r;
    float dot_y = sin(a * 2 * M_PI) * r;
    canvas->SetPixel(center_x + dot_x, center_y + dot_y,
                     255, 0, 0);
    usleep(1 * 1000);  // wait a little to slow down things.
  }
}

int main(int argc, char *argv[]) {
  /*
   * Set up GPIO pins. This fails when not running as root.
   */
  GPIO io;
  if (!io.Init())
    return 1;
    
  /*
   * Set up the RGBMatrix. It implements a 'Canvas' interface.
   */
  int rows = 32;    // A 32x32 display. Use 16 when this is a 16x32 display.
  int chain = 1;    // Number of boards chained together.
  int parallel = 1; // Number of chains in parallel (1..3). > 1 for plus or Pi2
  Canvas *canvas = new RGBMatrix(&io, rows, chain, parallel);

  DrawOnCanvas(canvas);    // Using the canvas.

  // Animation finished. Shut down the RGB matrix.
  canvas->Clear();
  delete canvas;

  return 0;
}