SDL2 messed up image with manipulating pixels and SDL_UpdateTexture() - c

Question

I'm trying to make a simple image viewer. I basically load an image into a surface and then create a texture from it.
At the end, I do the usual SDL_RenderClear(), SDL_RenderCopy() and SDL_RenderPresent() as per the migration guide.
This works fine, except that if I call SDL_UpdateTexture() before the 3 render calls above, I get a messed up image:
I am calling SDL_UpdateTexture() like this:
SDL_UpdateTexture(texture, NULL, image->pixels, image->pitch)
Where image is the surface I loaded for the image and texture is the texture I created from that. Attempts to vary the pitch result in differently messed up images. I also tried using a rect for the second parameter, but results are the same if the rect has the same dimensions as the image. If the dimensions are larger (e.g. same as the window), the update doesn't happen, but there are no errors.
The full code is available.
I would like to manipulate pixels of the surface directly via image->pixels and then call SDL_UpdateTexture(), but just calling SDL_UpdateTexture() without any tampering is enough to mess things up.

Answer 1

I think there is something wrong with the pitch or the SDL_Rect parameters,
but there is another SDL function which might help:
SDL_Texture* SDL_CreateTextureFromSurface(SDL_Renderer* renderer,
SDL_Surface* surface)

Answer 2

Could you maybe try the following. It should replace any pink (r=255,g=0,b=255) pixels to be transparent. You would simply change the pixel32 manipulation to accommodate your needs.
SDL_Surface* image = IMG_Load(filename);
SDL_Surface* imageFomatted = SDL_ConvertSurfaceFormat(image,
SDL_PIXELFORMAT_RGBA8888,
NULL);
texture = SDL_CreateTexture(renderer,
SDL_PIXELFORMAT_RGBA8888,
SDL_TEXTUREACCESS_STREAMING,
imageFomatted->w, imageFomatted->h);
void* pixels = NULL;
int pitch = 0;
SDL_LockTexture(texture, &imageFomatted->clip_rect, &pixels, &pitch);
memcpy(pixels, imageFomatted->pixels, (imageFomatted->pitch * imageFomatted->h));
int width = imageFomatted->w;
int height = imageFomatted->h;
Uint32* pixels32 = (Uint32*)pixels;
int pixelCount = (pitch / 4) * height;
Uint32 colorKey = SDL_MapRGB(imageFomatted->format, 0xFF, 0x00, 0xFF);
Uint32 transparent = SDL_MapRGBA(imageFomatted->format, 0xFF, 0x00, 0xFF, 0x00);
for (int i = 0; i < pixelCount; i++) {
if (pixels32[i] == colorKey) {
pixels32[i] = transparent;
}
}
SDL_UnlockTexture(texture);
SDL_FreeSurface(imageFormatted);
SDL_FreeSurface(image);
pixels = NULL;
pitch = 0;
width = 0;
height = 0;