Search code examples
c++cimagebitmapsdl

SDL embed image inside program executable

Is it possible to embed an image within a program using SDL which can be used at run time.

For example, I have a program which brings up a splash screen on startup containing the logo and copyright information. Rather than having this image in a bitmap file and using SDL_LoadBMP to load it to a SDL_Surface. I would like to have the image embedded in the program binary, to stop someone potentially changing the splash image and copyright name.

Does anyone have any suggestions on ways to do this? Example code would be great.

Solution

  • Embedding a file in an executable is easy but there are some gotchas, there are several ways to do it including some portable and non-portable ways.

    Using #embed

    This will reportedly be part of C23. It may be on track to appear in C++26 as well. Check whether your compiler supports this feature. In the future, this may be the most portable and straightforward way to embed binary data.

    static const unsigned char IMAGE_DATA[] = {
#embed "myimage.bmp
};

    See WG14 n2592 for the feature proposal.

    Advantages: simplest, easiest

    Disadvantages: your compiler probably doesn’t support this yet

    Convert the image to C code

    Write a script to convert the image to a constant array in C. The script would look something like this in Python:

    #!/usr/bin/env python3
print("static const unsigned char IMAGE_DATA[] = {{{}}};".format(
        ",".join(str(b) for b in open("myimage.bmp", "rb").read())))

    Just pipe the output to a *.h file and include that file from one other file. You can get the size of the file with sizeof(IMAGE_DATA).

    Advantages: portable

    Disadvantages: requires Python to be installed, does not work if array is too large for compiler, requires adding a custom step to the build system

    Convert the image to an object file

    This is more platform-dependent. On platforms with GNU binutils toolchains (e.g. Linux) you can use objcopy, I think bin2obj works on Microsoft toolchains.

    Advantages: works everywhere

    Disadvantages: non-portable, requires adding a custom step to the build system, the custom step might be tricky to get right

    On GNU binutils toolchains, with objcopy

    The objcopy program lets you specify binary as the input format, but then you need to specify the architecture explicitly... so you will have to modify the command for i386 and x64 versions of your executable.

    $ objcopy --input binary --output elf32-i386 --binary-architecture i386 \
    myimage.bmp myimage.o

    You can get the data from C by using the following declarations:

    // Ignore the fact that these are char...
extern char _binary_myimage_bmp_start, _binary_myimage_bmp_end;

#define MYIMAGE_DATA ((void *) &_binary_myimage_bmp_start)
#define MYIMAGE_SIZE \
    ((size_t) (&_binary_myimage_bmp_end - &_binary_myimage_bmp_start))

    Use an assembler directive

    Paradoxically, embedding a static file is fairly easy in assembler. Assemblers often have directives like .incbin (which works with GAS and YASM).

    Advantages: works everywhere

    Disadvantages: non-portable, assembler syntax is different between platforms

    (Windows) Embed the file as a resource

    On Windows, you can embed resources in an EXE and then get the resources using library calls.

    Advantages: probably easiest if you are on Windows

    Disadvantages: only works on Windows