SDL_Surface* SDL_CreateRGBSurfaceFrom(void*  pixels,
                                      int    width,
                                      int    height,
                                      int    depth,
                                      int    pitch,
                                      Uint32 Rmask,
                                      Uint32 Gmask,
                                      Uint32 Bmask,
                                      Uint32 Amask)

// This example shows how to create a SDL_Surface* with the data loaded from an image
// file with the stb_image.h library (https://github.com/nothings/stb/)

// the color format you request stb_image to output,
// use STBI_rgb if you don't want/need the alpha channel
int req_format = STBI_rgb_alpha;
int width, height, orig_format;
unsigned char* data = stbi_load("./test.png", &width, &height, &orig_format, req_format);
if(data == NULL) {
  SDL_Log("Loading image failed: %s", stbi_failure_reason());
  exit(1);
}

// Set up the pixel format color masks for RGB(A) byte arrays.
// Only STBI_rgb (3) and STBI_rgb_alpha (4) are supported here!
Uint32 rmask, gmask, bmask, amask;
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
  int shift = (req_format == STBI_rgb) ? 8 : 0;
  rmask = 0xff000000 >> shift;
  gmask = 0x00ff0000 >> shift;
  bmask = 0x0000ff00 >> shift;
  amask = 0x000000ff >> shift;
#else // little endian, like x86
  rmask = 0x000000ff;
  gmask = 0x0000ff00;
  bmask = 0x00ff0000;
  amask = (req_format == STBI_rgb) ? 0 : 0xff000000;
#endif

int depth, pitch;
if (req_format == STBI_rgb) {
  depth = 24;
  pitch = 3*width; // 3 bytes per pixel * pixels per row
} else { // STBI_rgb_alpha (RGBA)
  depth = 32;
  pitch = 4*width;
}

SDL_Surface* surf = SDL_CreateRGBSurfaceFrom((void*)data, width, height, depth, pitch,
                                             rmask, gmask, bmask, amask);

if (surf == NULL) {
  SDL_Log("Creating surface failed: %s", SDL_GetError());
  stbi_image_free(data);
  exit(1);
}

// ... do something useful with the surface ...
// ...

// when you don't need the surface anymore, free it..
SDL_FreeSurface(surf);
// .. *and* the data used by the surface!
stbi_image_free(data);