Port of the official spine-sfml runtime to use SDL2 instead of SFML. It uses the new SDL_RenderGeometry functionality introduced in SDL2 2.0.18.

Just like spine-sfml, two different flavors are offered: one based on spine-c and one based on spine-cpp. They are in the c and cpp folders respectively.

• Spine animations exported for runtime 4.0.*
• SDL2 ≥ 2.0.18 and SDL_Image
• I also tested it with Emscripten 3.1.9.

See the c or cpp folders for examples and documentation.

1. The starting point was spine-sfml from the 4.0 branch. Since this implementation is part of the official runtimes, I tried to keep the logic unchanged.

2. I made some small improvements, such as:

   • Made getUsePremultipliedAlpha() const
   • Refactored the blend mode logic into a single switch statement. Same performance, half the lines, more readable.
   • spine-c version only:
     • Removed the manual implementation for spColorArray and used the _SP_ARRAY_IMPLEMENT_TYPE macro instead. This change required the operator== to be defined, but this is cleaner than writing the entire implementation by hand.

3. Replaced SFML with SDL2 as follows:

   • Using the _SP_ARRAY macros, I created a new array type spVertexArray based on SDL_Vertex and replaced all references to sf::VertexArray with it.
   • Defined the blend modes with SDL_ComposeCustomBlendMode using GerogeChong's code as a starting point.
   • Used SDL_SetTextureBlendMode and SDL_RenderGeometry for drawing. It's roughtly equivalent to what rmg-nik's did.
   • spine-c version only:
     • Implemented _spUtil_readFile using SDL_RWFromFile, SDL_RWread, etc.
     • Implemented _spAtlasPage_createTexture/_spAtlasPage_disposeTexture using IMG_Load and SDL_CreateTextureFromSurface.
     • Important: the previous step depends on a external function called spSDL_getRenderer that you have to implement yourself, but it's very easy: just return a pointer to the current SDL_Renderer
   • spine-cpp version only:
     • Replaced SFMLTextureLoader with a new class SDLTextureLoader implemented using IMG_Load and SDL_CreateTextureFromSurface. The constructor takes a pointer to the current SDL_Renderer (so there's no need to define an external function).

4. Modified the examples from spine-sfml to use spine-sdl:

   • Replaced the SFML loops with standard SDL loops.
   • Replaced sf::Mouse::getPosition, window.clear() and window.display() with SDL_GetMouseState, SDL_RenderClear and SDL_RenderPresent respectively.
   • Commented out the mix blends in the owl example because they don't seem to be working as intended.
   • Fixes to the c examples:
     • Leak #1: Calls to spAnimationStateData_dispose were missing.
     • Leak #2: SkeletonDrawable instances never get deleted, but we can create them on the stack like the cpp examples do.