RenderCopy or RenderCopyEx

svanimpe · January 30, 2022, 5:24pm

Hi everyone,

What’s the difference between the following two calls, and is there a reason I should prefer one over the other?

SDL_RenderCopy(renderer, texture, NULL, NULL)
SDL_RenderCopyEx(renderer, texture, NULL, NULL, 0, NULL, SDL_FLIP_NONE)

I’m asking because I’m building a higher-level framework on top of SDL and I was wondering if can always just call SDL_RenderCopyEx, or if there are cases where I should prefer SDL_RenderCopy

I’ve also noticed that SDL_RenderCopyExF delegates to SDL_RenderCopyF when no transformation is required:

github.com

libsdl-org/SDL/blob/a5c610b0a3857d3138f3f3da1f6dc3172c5ea4a8/src/render/SDL_render.c#L3601

    
      
                         const SDL_Rect * srcrect, const SDL_FRect * dstrect,
                         const double angle, const SDL_FPoint *center, const SDL_RendererFlip flip)
          {
              SDL_Rect real_srcrect;
              SDL_FRect real_dstrect;
              SDL_FPoint real_center;
              int retval;
              int use_rendergeometry;
          
          
    if (flip == SDL_FLIP_NONE && (int)(angle/360) == angle/360) { /* fast path when we don't need rotation or flipping */
                  return SDL_RenderCopyF(renderer, texture, srcrect, dstrect);
              }
          
          
    CHECK_RENDERER_MAGIC(renderer, -1);
              CHECK_TEXTURE_MAGIC(texture, -1);
          
          
    if (renderer != texture->renderer) {
                  return SDL_SetError("Texture was not created with this renderer");
              }
              if (!renderer->QueueCopyEx && !renderer->QueueGeometry) {
                  return SDL_SetError("Renderer does not support RenderCopyEx");

Mason_Wheeler · January 30, 2022, 7:57pm

svanimpe:

What’s the difference between the following two calls, and is there a reason I should prefer one over the other?
SDL_RenderCopy(renderer, texture, NULL, NULL)
SDL_RenderCopyEx(renderer, texture, NULL, NULL, 0, NULL, SDL_FLIP_NONE)

The answer is right there in the question. If that’s all you’re doing, just call SDL_RenderCopy. It’s smaller and simpler. But if what you’re trying to render won’t work without non-default values for those extra parameters, well, that’s when it’s good to have a bigger API available that can take more detailed information in its input.

svanimpe · January 31, 2022, 9:22am

I’m working in Swift, so my function calls are already much cleaner and simpler. I also have no need for separate functions, as I can just use parameters with default values. So I’m left wondering whether I should differentiate between Copy and CopyEx in my implementation.

Given that the implementation of SDL_RenderCopyExF bothers to check and delegate to SDL_RenderCopyF if possible, and that there are separate QueueCopyEx and QueueCopy functions, I get the impression that there’s a difference (in performance?) between the two.