Is using a width less than zero portable behaviour in SDL2 - c

Question

I am making use of what looks like a bit of a cheat of SDL2's SDL_Rect struct. In my program I wanted a rectangle to "grow" from the right to the left side of the screen. To do this I tried to decrement the width attribute of the rect below zero and, in fact, it has the correct effect. However, I am left with the question of is this correct, portable behaviour. I understand that in the real world it does not make sense to have a rectangle with a negative width. However, it seems that the SDL developers may have intended for this to be the case. In SDL1.2 the SDL_Rect structure was defined as using an unsigned integer to represent the width and height whereas in SDL2 the SDL_Rect uses signed integers. Included below is code that exhibits this "cheat", error checking omitted for brevity.
#include <stdio.h>
#include <stdbool.h>
#include <SDL2/SDL.h>
#define SCREEN_W 640
#define SCREEN_H 480
int main(int argc, char** argv)
{
SDL_Init(SDL_INIT_VIDEO)
SDL_Window* window = SDL_CreateWindow("test", 110, 110, SCREEN_W, SCREEN_H, 0);
SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_PRESENTVSYNC);
SDL_Rect rects[5];
for(int i = 0; i < 5; i++)
{
rects[i].w = 0;
rects[i].h = (SCREEN_H / 5);
rects[i].x = (i % 2) * SCREEN_W;
rects[i].y = i * (SCREEN_H / 5);
}
SDL_Event e;
bool running = true;
while(running)
{
while (SDL_PollEvent(&e)) {
if (e.type == SDL_QUIT)
{
running = false;
}
}
SDL_SetRenderDrawColor(renderer, 255, 255, 255, SDL_ALPHA_OPAQUE);
SDL_RenderClear(renderer);
SDL_SetRenderDrawColor(renderer, 0, 0, 0, SDL_ALPHA_OPAQUE);
for(int i = 0; i < 5; i++)
{
SDL_RenderFillRect(renderer, &rects[i]);
if (i % 2 == 0)
{
rects[i].w++;
}
else
{
rects[i].w--;
}
}
if (rects[0].w == SCREEN_W)
{
for(int i = 0; i < 5; i++)
{
rects[i].w = 0;
}
}
SDL_RenderPresent(renderer);
}
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return EXIT_SUCCESS;
}
I will reiterate, I do not think this invokes any undefined behaviour but I am unsure if this is portable behaviour within the context of SDL2. Should I expect my code to work on everyone's machine today and going forward?