A reusable C++ class for generating an image and saving it as a PNG file via lodepng.

VideoFrame.cpp

class VideoFrame
{
private:
    int width;
    int height;
    std::vector<unsigned char> buffer;

public:
    VideoFrame(int _width, int _height)
        : width(_width)
        , height(_height)
        , buffer(4 * _width * _height, 255)
        {}

    void SetPixel(int x, int y, PixelColor color)
    {
        int index = 4 * (y*width + x);
        buffer[index]   = color.red;
        buffer[index+1] = color.green;
        buffer[index+2] = color.blue;
        buffer[index+3] = color.alpha;
    }

    int SavePng(const char *outFileName)
    {
        unsigned error = lodepng::encode(outFileName, buffer, width, height);
        if (error)
        {
            fprintf(stderr, "ERROR: lodepng::encode returned %u\n", error);
            return 1;
        }
        return 0;
    }
};