Where I started

My introduction to SameBoy came from stacksmashing’s “How to reverse engineer & patch a Game Boy ROM” video.

I’m not big on reverse engineering but I do enjoy a good GameBoy game when I see one.

and there it was

this is the type of integration I like to see from projects

but these kinds of features are almost never present on Linux be it because no one bothers or because each major DE supports a different method.

Despite that I was interested in it and started looking through the code

pretty images for pretty games

the code was simple it stored the framebuffer output in a bitmap image and composed that under the image for the cartridge case.

Seems simple

(source code)

            bitmap* pbitmap  = malloc(sizeof(bitmap));
            pbitmap->fileheader.signature[0] = 0x42;
            pbitmap->fileheader.signature[1] = 0x4D;

            pbitmap->fileheader.filesize = sizeof(pixels) + sizeof(bitmap);
            pbitmap->fileheader.fileoffset_to_pixelarray = sizeof(bitmap);
            pbitmap->bitmapinfoheader.dibheadersize = sizeof(bitmapinfoheader);
            pbitmap->bitmapinfoheader.width = 160;
            pbitmap->bitmapinfoheader.height = -144;
            pbitmap->bitmapinfoheader.planes = 1;
            pbitmap->bitmapinfoheader.bitsperpixel = 32;
            pbitmap->bitmapinfoheader.compression = 0;
            pbitmap->bitmapinfoheader.imagesize = sizeof(pixels);
            pbitmap->bitmapinfoheader.ypixelpermeter = 0;
            pbitmap->bitmapinfoheader.xpixelpermeter = 0;
            pbitmap->bitmapinfoheader.numcolorspallette = 0;
            fwrite(pbitmap, 1, sizeof(bitmap),fp);
            fwrite(pixels, 1, sizeof(pixels),fp);
            fclose(fp);
            free(pbitmap);

I actually wanted to see the images in my filemanager though so I went to see how that is done and quickly changed my mind.

The way you creat ThumbCreator plugins for KDE was way too complicated to propose to the repository so I went Freedesktop Thumbnailer standard instead

the biggest requirement was that the output format was a PNG so I started from scratch

writing my own png lib was too big of an undertaking so I simply chose to use lodepng, a free png library under zlib so it was fair to use

a simple conversion to PNG was completed and the resulting binary outputted pngs for any files you wanted

I was happy with this but it was a bit bare and having to specify the bootrom path wasn’t very user friendly so I took suggestions from max-m and embedded everything needed in the binary itself

but the image does need to be resized if a differnt resolution was desired

so I implemented a basic scaling function with things like passable sample size

(source code)

static void scale_image(const uint32_t* input, const signed input_width, const signed input_height,
                        uint32_t* output, const double multiplier, const signed samples)
{
    signed output_width = input_width * multiplier;
    uint32_t pixel;

    for (signed h = 0; h < input_height * multiplier; ++h) {
        for (signed w = 0; w < input_width * multiplier; ++w) {
            pixel = 0;

            signed h_input = h/multiplier;
            signed w_input = w/multiplier;

            signed h_input_max = (h+1)/multiplier-1;
            signed w_input_max = (w+1)/multiplier-1;

            signed h_step = h_input_max - h_input + 2;
            signed w_step = w_input_max - w_input + 2;

            for (signed xa = w_input; xa < w_input_max + 2 && xa < input_width; xa += w_step / samples)
                for (signed ya = h_input; ya < h_input_max + 2 && ya < input_width; ya += h_step / samples)
                    pixel = average(pixel, input[(signed)xa + ((signed)ya * input_width)]);

            output[w + (h * output_width)] = pixel;
        }
    }
}