Using SDL_BlitScaled to created scaled copies of surfaces - c

Question

So I'm working on some SDL2 Wrapper stuff, and I'm trying to use SDL_BlitScaled to copy the data in a src surface into a destination surface which I've already created, like so
SDL_Surface *loaded = IMG_Load("test.png");
SDL_SetSurfaceBlendMode(loaded, SDL_BLENDMODE_NONE);
SDL_Surface *out = SDL_CreateRGBSurface(0, 100, 100, loaded->format->BitsPerPixel,
loaded->format->Rmask, loaded->format->Gmask, loaded->format->Bmask, loaded->format->Amask);
SDL_BlitScaled(loaded, NULL, out, NULL);
SDL_Texture *tex = SDL_CreateTextureFromSurface(ren, out);
SDL_Rect rec = {10, 10, 110, 110};
SDL_RenderCopy(ren, tex, NULL, &rec);
Don't worry about my renderer or window etc. I've isolated the problem to somewhere in this code. The image does not appear on the screen, however it does if I create a texture from the loaded surface. Thoughts? I imagine I'm misusing either CreateRGBSurface, or BlitScaled (I did see another question about this, however the solution was unclear).

Answer 1

For me I had to do:
SDL_SetSurfaceBlendMode(loaded , SDL_BLENDMODE_NONE);
SDL_SetSurfaceBlendMode(out, SDL_BLENDMODE_NONE);
For it to work, otherwise some strange blending happens.
The docs page for this function says:
To copy a surface to another surface (or texture) without blending with the existing data, the blendmode of the SOURCE surface should be
set to 'SDL_BLENDMODE_NONE'.
So setting loaded is probably enough.
Edit: In the end I came up with this:
struct FreeSurface_Functor
{
void operator() (SDL_Surface* pSurface) const
{
if (pSurface)
{
SDL_FreeSurface(pSurface);
}
}
};
typedef std::unique_ptr<SDL_Surface, FreeSurface_Functor> SDL_SurfacePtr;
class SDLHelpers
{
public:
SDLHelpers() = delete;
static SDL_SurfacePtr ScaledCopy(SDL_Surface* src, SDL_Rect* dstSize)
{
SDL_SurfacePtr scaledCopy(SDL_CreateRGBSurface(0,
dstSize->w, dstSize->h,
src->format->BitsPerPixel,
src->format->Rmask, src->format->Gmask, src->format->Bmask, src->format->Amask));
// Get the old mode
SDL_BlendMode oldBlendMode;
SDL_GetSurfaceBlendMode(src, &oldBlendMode);
// Set the new mode so copying the source won't change the source
SDL_SetSurfaceBlendMode(src, SDL_BLENDMODE_NONE);
// Do the copy
if (SDL_BlitScaled(src, NULL, scaledCopy.get(), dstSize) != 0)
{
scaledCopy.reset();
}
// Restore the original blending mode
SDL_SetSurfaceBlendMode(src, oldBlendMode);
return scaledCopy;
}
};