2D Terrain Generation Sample

Terrain2D.cpp

#include <iostream>
#include <vector>
#include <random>
#include <string>
#include <cstdint>
#include <cstring>
#include <ctime>

#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"
using namespace std;

static constexpr int PixelSize = 3;
static mt19937 mt(time(nullptr));

void Paint(uint8_t* pixel, const uint8_t* color)
{
    memcpy(pixel, color, PixelSize);
}

void GenerateWorldMap(int width, int height, const char* path)
{
    if (width < 1 || height < 1)
    {
        cout << "invalid map size: (" << width << ")x(" << height << ")\n";
        return;
    }
    
    int pixelCount = width * height;
    
    const uint8_t SkyBlue[] = {0x84, 0xaa, 0xf8, 0x00};
    const uint8_t DirtBrown[] = {0x97, 0x6b, 0x4b, 0x00};
    
    vector<double> elevations(width + 1);
    
    int w = width;
    double range = 1.0;
    
    while (w > 3)
    {
        int half = w / 2;
        uniform_real_distribution<double> distribution(-range, range);
        
        for (int i = 0; i < width; i += half)
        {
            auto delta = distribution(mt);
            double low = elevations[i];
            double high = (elevations[i + half] += delta);
            double gap = high - low;
            
            for (int j = 1; j < half; ++j)
            {
                double t = double(j) / double(half - 1);
                elevations[i + j] = gap * t + low; 
            }
        }
        
        range /= 2.0;
        w = half;
    }

    vector<uint8_t> bytes(width * height * PixelSize);
    auto data = bytes.data();
    
    auto GetPixel = [=](int x, int y)
    {
        return data + (y * width + x) * PixelSize;
    };
    
    int halfHeight = height / 2;
    for (int i = 0; i < width; ++i)
    {
        int elevation = halfHeight + int(elevations[i] * double(halfHeight));
        
        for (int j = 0; j < height; ++j)
        {
            auto pixel = GetPixel(i, j);
            Paint(pixel, j > elevation ? DirtBrown : SkyBlue);
        }
    }
    
    int result = stbi_write_png(
        path,
        width,
        height,
        PixelSize,
        data,
        width * PixelSize);
    
    if (result == 0)
    {
        cout << "failed to write image to " << path << '\n';
    }
    else
    {
        cout << "successfully wrote image to " << path << '\n';
    }
}

int main(int argc, char** argv)
{
    string path;
    for (int i = 0; i < 8; ++i)
    {
        path = "world";
        path += to_string(i + 1);
        path += ".png";
        GenerateWorldMap(1024, 256, path.data());
    }
    return 0;
}