How to get subimage with FreeImage

Question

As stated in the title, I am using FreeImage to load textures in my OpenGL game, but how do I get subimages?

My current code looks like this:

    FREE_IMAGE_FORMAT fif = FIF_UNKNOWN;
    FIBITMAP* dib = nullptr;
    fif = FreeImage_GetFileType(filename, 0);
    if (fif == FIF_UNKNOWN)
        fif = FreeImage_GetFIFFromFilename(filename);
    if (fif == FIF_UNKNOWN)
        return nullptr;

    if (FreeImage_FIFSupportsReading(fif))
        dib = FreeImage_Load(fif, filename);
    if (!dib)
        return nullptr;

    BYTE* pixels = FreeImage_GetBits(dib);
    *width = FreeImage_GetWidth(dib);
    *height = FreeImage_GetHeight(dib);
    *bits = FreeImage_GetBPP(dib);

    int size = *width * *height * (*bits / 8);
    BYTE* result = new BYTE[size];
    memcpy(result, pixels, size);
    FreeImage_Unload(dib);
    return result;

What would I need to change to get the subimage (for example a 32x32 area of pixels in the top left corner)?

Answer 1

You can use FreeImage_Copy() to get a subimage of a specified region. Note that FreeImage_Copy() takes left, top, right, bottom and not x, y, width, height.

FIBITMAP *image = ...;

int x = 0;
int y = 0;
int width = 32;
int height = 32;

FIBITMAP *subimage = FreeImage_Copy(image, x, y, x + width, y + height);

Remember to FreeImage_Unload(subimage) as it is a literal copy of the given image.

If needed you could then save it to a PNG by doing:

if (FreeImage_Save(FIF_PNG, subimage, "subimage.png"))
    printf("Subimage successfully saved!\n");
else
    printf("Failed saving subimage!\n");