Generating images with C++

Sometimes I need to generate some images with simple shapes for a little project, but i don’t want to install some heavy libraries, and this is why I decided to creaty my own single file library for simple image generation in C++: EasyBMP.

• Source Code

Full example: A 512x512 image with two Metaballs

#include "EasyBMP.hpp"
#include <iostream>
#include <vector>
#include <cmath>
using namespace std;

struct point
{
  double x, y;
  point(double _x, double _y) : x(_x), y(_y) { }
  double distanceTo(const point& o) {
    double dx = (x - o.x);
    double dy = (y - o.y);
    return sqrt(dx * dx + dy * dy);
  }
};

int main()
{
  vector< point > centers = {
    {256, 256},
    {192, 192}
  };
  vector< double > charges = {1024.0, 2048.0};
  // R, G, B [0, 255]
  EasyBMP::RGBColor black(0, 0, 0);  
  // sizeX, sizeY, FileName, BackgroundColor
  EasyBMP::Image img(512, 512, "sample.bmp", black);

  for (int y = 0; y < 512; ++y) {
    for (int x = 0; x < 512; ++x) {
      double intensity = 0.0;
      for (int i = 0; i < 2; ++i) {
        double dist = max(centers[i].distanceTo(point(x, y)), 1.0);
        intensity += charges[i] / (dist * dist);
      }
      int final_color = min(255, int(255. * intensity));
      // PositionX, PisitionY, Color
      img.SetPixel(x, y, EasyBMP::RGBColor(final_color, final_color, 0));
    }
  }
  img.Write();
  return 0;
}

Result:

EasyBMP

EasyBMP is an easy to use library to generate BMP images with a simple structure to prototype any project with image generation requirement.

The API it’s really simple.

The namespace it’s EasyBMP. This little tutorial won’t use “using namespace”.

You have 2 classes (EasyBMP::Image, EasyBMP::RGBColor).

EasyBMP::RGBColor

---

EasyBMP::RGBColor just have 2 constructors:

EasyBMP::RGBColor(uint8_t r, uint8_t g, uint8_t b); // Just r,g,b
EasyBMP::RGBColor(); // Empty constructor, you need to assign values manually

This means that you have two ways to create an instance of EasyBMP::RGBColor:

// Using the rgb constructor:
EasyBMP::RGBColor yellow1 = EasyBMP::RGBColor(255, 255, 0);

// Or using the void constructor and set values manually using SetColor:
EasyBMP::RGBColor yellow2;
yellow2.SetColor(255, 255, 0);

EasyBMP::SetColor is defined as:

RGBColor::SetColor(uint8_t r, uint8_t g, uint8_t b);

I personally recommend to use the first option because code may have some errors if you forget to set color.

You can also acces variables using .r, .g or .b:

EasyBMP::RGBColor yellow1 = EasyBMP::RGBColor(255, 255, 0);
uint8_t yellow1_green = yellow1.g;

EasyBMP::Image

---

You have some constructors to create an instance of an EasyBMP::Image from scratch:

EasyBMP::Image(int64_t width, int64_t height);
EasyBMP::Image(int64_t width, int64_t height, string fileName);
EasyBMP::Image(int64_t width, int64_t height, RGBColor backgroundColor);
EasyBMP::Image(int64_t width, int64_t height, string fileName, RGBColor backgroundColor);

For example:

/*
This will create an image "img" with size 512x512,
on a file "sample.bmp", and the background will be yellow.
*/
EasyBMP::Image img(512, 512, "sample.bmp", EasyBMP::RGBColor(255, 255, 0));

And some others to create an instance of an EasyBMP::Image from an already existing bitmap:

EasyBMP::Image(const string& _inFileName);
EasyBMP::Image(const string& _inFileName, const string& _outFileName);

For example:

/*
This will create an image "img" by loading "input.bmp".
"img" will be written to a new file named "output.bmp".
*/
EasyBMP::Image img("input.bmp", "output.bmp");

To modify a single pixel, you can use EasyBMP::Image::SetPixel:

img.SetPixel(x, y, EasyBMP::RGBColor(r, g, b));

Defined as:

EasyBMP::Image::SetPixel(int64_t x, int64_t y, RGBColor color);

And to get a pixel value, EasyBMP::Image::GetPixel:

img.GetPixel(x, y);

Defined as:

const RGBColor& EasyBMP::Image::GetPixel(int64_t x, int64_t y) const;