#include <random>

​

void paintOctopus(float x, float y, int size_base, SkColor color, SkCanvas* canvas) {

    // Set up the paint to draw the head and legs

    SkPaint paint;

    paint.setAntiAlias(true);

    paint.setColor(color);

    int radius = 3*size_base;

    // Draw the big head

    canvas->drawCircle(x, y, radius, paint);

    // Draw 8 small legs

    for (int leg = 0; leg < 8; ++leg) {

      canvas->drawCircle(x - radius + (2*radius/7.5*leg),

                         y + radius - pow(abs(4-leg), 2), size_base/2 + 2, paint);

    }

    // Make the color a bit lighter for the eyes

    paint.setColor(SkColorSetRGB(std::min(255u, SkColorGetR(color) + 20),

                                 std::min(255u, SkColorGetG(color) + 20),

                                 std::min(255u, SkColorGetB(color) + 20)));

    // Draw the left and right eye

    canvas->drawCircle(x-size_base, y+size_base, size_base/2, paint);

    canvas->drawCircle(x+size_base, y+size_base, size_base/2, paint);

}

​

void draw(SkCanvas* canvas) {

    // This is called many times, once per frame. To keep the octopods

    // a consistent color, we depend on the RNG using the *same* seed

    // for each of calls (i.e. don't reseed it based on time or something).

    std::default_random_engine rng;

    const auto randScalar = [&rng](float min, float max) -> float {

        return std::uniform_real_distribution<float>(min, max)(rng);

    };

    const auto randInt = [&rng](int min, int max) -> int {

        return std::uniform_int_distribution<int>(min, max)(rng);

    };

    const auto randOpaqueColor = [&rng]() -> SkColor {

        return std::uniform_int_distribution<uint32_t>(0, 0xFFFFFF)(rng) | 0xFF000000;

    };

​

    // Don't make this too big or rendering will time out.

    constexpr int numOctopods = 20;

    for (int i = 0; i < numOctopods; ++i) {

      float x = randScalar(0, 256);

      float y = randScalar(0, 256);

      int s = randInt(6, 12);

      SkColor c = randOpaqueColor();

      // To make the octopods "swim" we have them move around a circle

      // of a random radius

      float radius = randScalar(0, 40);

      // frame is in range [0, 1.0], so this starts at some fraction of 2pi

      // (e.g. 1/2 pi) and goes until that fraction + 2pi (e.g. 5/2 pi)

      float angle = (randScalar(0, 1) + frame) * 6.28319;

      x += radius * cos(angle);

      y += radius * sin(angle);

      paintOctopus(x, y, s, c, canvas);

    }

}