[josephg]

On the allocation point, the efficient way to handle this is to use a per-frame memory pool. Because nothing in the IMGUI can persist between frames, you can allocate a single arena of memory for any UI elements that need to store bounding boxes or callbacks or whatever. Each frame just reset your next_ptr to the start of the arena. Technically you are allocating memory, but in practice your allocations are free.

[geezerjay]

Adding a separate complex ad hoc memory allocation scheme is not what I would call free. Granted, computationally-wise it may be relatively cheap but it does add multiple forms of complexity to a problem that doesn't exist in rmguis.

[loup-vaillant]

Arenas are the simplest allocation scheme ever.

  // Start of frame
  void *arena    = malloc(LOTS_OF_MEMORY);
  void *next_ptr = arena;

  // Allocate something
  object   = *next_ptr;               // return that value
  next_ptr = object_size + alignment; // crash if out of memory
 
  // End of frame
  free(arena);

By the way, such "separate complex ad hoc" memory allocation schemes are the reason why manual memory management is faster than garbage collection. If you did everything with malloc(), it would be slower (unless the GC language allocates much more than C, which they often do).

[Keyframe]

No need to malloc each frame. Malloc at startup and memset each frame (don't even need to do that, tbh).

[maccard]

Nope, just set the pointer back to where it started from. You do need to be super careful doing this though, as anything that relies on RAII (in c++ land) will be busted. You could manually call the destructor on the object in that case, but kind of defeats the purpose of the "no allocation" goals

[geezerjay]

C++ includes it's "placement new" feature specifically to cater to the memory pool needs. There's no allocation, and only constructor and destructor calls.

[tom_]

It’s a good idea to have a mode that does malloc every frame, as that makes stale pointers much easier to find.

[brann0]

A memory arena that is reset every render loop is the simplest memory allocation possible.

[sly010]

Where do you store pointers to textures? Or do you upload textured to the GPU every frame? What about scroll positions an other non application state?