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Adding support for a RenderCopy operation flipped around the X, Y or both axes.

Add the following two definitions to SDL_render.h:

typedef enum
{
	SDL_RENDERFLIP_HORIZ = 0x00000001,
	SDL_RENDERFLIP_VERT  = 0x00000002,
	SDL_RENDERFLIP_BOTH  = 0x00000003
} SDL_RenderFlip;

...

/**
 *  \brief Copy a portion of the texture to the current rendering target, flipped
 *         around one or both axes.
 *  
 *  \param texture The source texture.
 *  \param srcrect   A pointer to the source rectangle, or NULL for the entire 
 *                   texture.
 *  \param dstrect   A pointer to the destination rectangle, or NULL for the 
 *                   entire rendering target.
 *  \param axes      Which axes to flip the image around.
 *  
 *  \return 0 on success, or -1 on error
 */
extern DECLSPEC int SDLCALL SDL_RenderCopyFlipped(SDL_Renderer * renderer,
		  SDL_Texture * texture,
		  const SDL_Rect * srcrect,
		  const SDL_Rect * dstrect,
		  SDL_RenderFlip axes);



Then replace the implementation of SDL_RenderCopy with:

SDL_bool SDL_ClipRects(SDL_Renderer * renderer, SDL_Texture * texture,
               const SDL_Rect * srcrect, const SDL_Rect * dstrect,
			   SDL_Rect * real_srcrect, SDL_Rect * real_dstrect)
{
    real_srcrect->x = 0;
    real_srcrect->y = 0;
    real_srcrect->w = texture->w;
    real_srcrect->h = texture->h;
    if (srcrect) {
        if (!SDL_IntersectRect(srcrect, real_srcrect, real_srcrect)) {
			return SDL_FALSE;
        }
    }

    real_dstrect->x = 0;
    real_dstrect->y = 0;
    real_dstrect->w = renderer->viewport.w;
    real_dstrect->h = renderer->viewport.h;
    if (dstrect) {
        if (!SDL_IntersectRect(dstrect, real_dstrect, real_dstrect)) {
            return SDL_FALSE;
        }
        /* Clip srcrect by the same amount as dstrect was clipped */
        if (dstrect->w != real_dstrect->w) {
            int deltax = (real_dstrect->x - dstrect->x);
            int deltaw = (real_dstrect->w - dstrect->w);
            real_srcrect->x += (deltax * real_srcrect->w) / dstrect->w;
            real_srcrect->w += (deltaw * real_srcrect->w) / dstrect->w;
        }
        if (dstrect->h != real_dstrect->h) {
            int deltay = (real_dstrect->y - dstrect->y);
            int deltah = (real_dstrect->h - dstrect->h);
            real_srcrect->y += (deltay * real_srcrect->h) / dstrect->h;
            real_srcrect->h += (deltah * real_srcrect->h) / dstrect->h;
        }
    }
	return SDL_TRUE;
}

int
SDL_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,
               const SDL_Rect * srcrect, const SDL_Rect * dstrect)
{
    SDL_Rect real_srcrect;
    SDL_Rect real_dstrect;

    CHECK_RENDERER_MAGIC(renderer, -1);
    CHECK_TEXTURE_MAGIC(texture, -1);

    if (renderer != texture->renderer) {
        SDL_SetError("Texture was not created with this renderer");
        return -1;
    }

	if (!SDL_ClipRects(renderer, texture, srcrect, dstrect, &real_srcrect,
		          &real_dstrect))
	  return 0;

    if (texture->native) {
        texture = texture->native;
    }

    return renderer->RenderCopy(renderer, texture, &real_srcrect,
                                &real_dstrect);
}

int
SDL_RenderCopyFlipped(SDL_Renderer * renderer, SDL_Texture * texture,
                      const SDL_Rect * srcrect, const SDL_Rect * dstrect,
					  int axes)
{
    SDL_Rect real_srcrect;
    SDL_Rect real_dstrect;

    CHECK_RENDERER_MAGIC(renderer, -1);
    CHECK_TEXTURE_MAGIC(texture, -1);

    if (renderer != texture->renderer) {
        SDL_SetError("Texture was not created with this renderer");
        return -1;
    }

	if (!SDL_ClipRects(renderer, texture, srcrect, dstrect, &real_srcrect,
		          &real_dstrect))
	  return 0;

    if (texture->native) {
        texture = texture->native;
    }

	if (axes & SDL_RENDERFLIP_HORIZ)
	{
		real_dstrect.x += real_dstrect.w;
		real_dstrect.w *= -1;
	}

	if (axes & SDL_RENDERFLIP_VERT)
	{
		real_dstrect.y += real_dstrect.h;
		real_dstrect.h *= -1;
	}

    return renderer->RenderCopy(renderer, texture, &real_srcrect,
                                &real_dstrect);
}