How do I render to a texture loaded from a PNG file using SDL2

Question

I'm trying to create a simple 2D game using C++ and SDL2.

I thought it would be a good idea to go for a "layered" rendering model.

I would render my background first, then the world, then the constructs (things like building etc.), then the objects (NPC's etc.) and lastly a toggle-able debug-overlay.

Right now I'm just trying to render a background and a debug overlay but I've hit a wall.

I can't seem to be able to render my debug-overlay on top of my background.

I've set blending mode to SDL_BLENDMODE_NONE for the background and SDL_BLENDMODE_BLEND for the debug overlay.

The problem is however, that my background is loaded from a PNG file, but when calling SDL_CreateTextureFromSurface() the texture access is set to SDL_TEXTURE_ACCESS_STATIC. (Which can't be used as a target if I understand correctly).

My question is: How can I circumvent this issue? How can I make my background "drawable"?

EDIT: Grammar

Answer 1

You don't actually want to render your debug UI to the background texture. You want to render the background texture to the screen, and then your debug UI to the screen.

So the code flow should look something like this:

SDL_RenderClear(renderer);

// Render background
SDL_RenderCopy(renderer, backgroundTexture, NULL, NULL);

// Render debug info.
RenderText(GetCurrentFPS(), 0, 0); // Or whatever your text rendering might look like.
SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
for (BoundingBox* box : GetAllBoundingBoxes()) {
    SDL_RenderDrawRect(renderer, box->GetRect());
}

SDL_RenderPresent(renderer);