Generates pretty images :-)

my-first-d-program.d

import std.stdio : File, fwrite;
import std.math : sqrt;

struct Header {
align (1):
    short bitmap = 0x4d42;
    long fileSize;
    int headerSize = this.sizeof;
    int dataOffset = 40;
    int width;
    int height;
    short planes = 1;
    short depth = 24;
    int compression = 0;
    int bitmapSize;
    int unknown4;
    int unknown5;
    int unknown6;
    int unknown7;
}

align (1) struct Pixel {
align (1):
    byte r;
    byte g;
    byte b;
}

void main(string[] args) {
    auto f = File("image.bmp", "w");

    const int width = 1024;
    const int height = 1024;
    const int centerJ = width / 2;
    const int centerI = height / 2;

    Pixel[height][width] image;

    for (int i = 0; i < height; ++i) {
        for (int j = 0; j < height; ++j) {
            const int distanceI = i - centerI;
            const int distanceJ = j - centerJ;

            const float pixelDistanceSq = distanceI * distanceI + distanceJ * distanceJ;
            const float pixelSizeSq = width * width + height * height;
            const float distance = 4 * sqrt(pixelDistanceSq) / sqrt(pixelSizeSq);

            image[height - i - 1][j].r = cast(byte) (255 * (distance + cast(float) j / width));
            image[height - i - 1][j].g = cast(byte) (255 * (distance + 1 - sqrt(cast(float) (j * j + i * i) / (width * width + height * height))));
            image[height - i - 1][j].b = cast(byte) (255 * (distance + cast(float) i / height));
        }
    }

    Header hdr = {
        fileSize : Header.sizeof + image.sizeof,
        width : width,
        height : height,
        bitmapSize: image.sizeof
    };

    fwrite(&hdr, hdr.sizeof, 1, f.getFP());
    fwrite(&image, image.sizeof, 1, f.getFP());
}