Draw growing rectangle on the same x/y.

Hello, so I’ve been creating a sandbox game, and I’ve implemented a texture creating + rendering function. I’ve setup this code:

// The 'Window' object is simply a struct to hold
// identifiers and values about the window. The
// window itself (SDL_Window* XWindow) appears
// in main().

// Code not useful here.
SDL_Rect RectID;
RectID.x = MouseID->ButtonX;
RectID.y = MouseID->ButtonY;
if (RectID.h < Window->Size.h &&
     RectID.w < Window->Size.w) {
     do {
    } while (RectID.h < Window->Size.h &&
                  Rect.ID.w < Window->Size.w &&
                  ShouldRender == true);

I’ve encountered 2 issue myself, one is that RenderCopy requires a constant (const) rectangle, the other is the loop depends on whether should it terminate based on the KeepWindowOpen value, which brings some inconsistency.

The thing I want to achieve is a growing rectangle, because I’m rendering water on a flat surface. I’m fine with using stop frames as well.

So my question is, is there a way to do the same thing but to actually make it work?
(I’m fine with using external libraries if SDL can’t provide that functionality).