SDL_CreateRenderer driver selection priority and fallback limits

Answer

When SDL_CreateRenderer is called with a driver index of -1, SDL proceeds as follows:

1. Check the environment variable SDL_HINT_RENDER_DRIVER. If it is set to a name that matches a compiled renderer, SDL attempts to create that renderer first.
2. If the hint is not set or the named driver fails to initialize, SDL walks through the list of render drivers that were registered during SDL_Init(SDL_VIDEO), trying each in the order they were added.
3. For each driver, SDL tests whether the driver’s capabilities satisfy the requested SDL_RendererFlags (e.g., SDL_RENDERER_ACCELERATED requires a driver that reports the SDL_RENDERER_ACCELERATED flag). The first driver that both matches the flags and can successfully create a rendering context is chosen.
4. If no driver satisfies the flags and SDL_RENDERER_SOFTWARE is allowed, the built‑in software fallback driver is used as the last resort.

Confirmed facts

• The hint SDL_HINT_RENDER_DRIVER is consulted before any other logic.
• SDL iterates over the drivers in the order they were registered during video initialization.
• The final driver can be inspected with SDL_GetRendererInfo after creation.

Likely explanation (build‑dependent)

The registration order depends on how SDL was compiled. In typical official builds:

• Windows: Direct3D → OpenGL → Metal (if available) → Vulkan → software.
• Linux/macOS: OpenGL → Vulkan → Metal → software.

When SDL_RENDERER_ACCELERATED is requested, SDL skips drivers that only expose SDL_RENDERER_SOFTWARE; the first driver that reports the accelerated flag and can create a context wins. If none succeed and the software flag is also permitted, the software driver is chosen.

Steps to verify the exact order for your build

1. Call SDL_GetNumRenderDrivers() to get N.
2. For i = 0 … N‑1, invoke SDL_GetRenderDriverInfo(i, &info) and record info.name and info.flags.
3. The sequence of info.name values reflects the registration order SDL will use when the hint is unset.
4. Optionally, set SDL_HINT_RENDER_DRIVER to each name in turn, call SDL_CreateRenderer(window, -1, desiredFlags), and observe which attempt succeeds.

Missing diagnostic detail

To give a definitive recommendation for your specific environment, please provide the output of the driver enumeration steps above (the list of driver names and their flags). Knowing which drivers are actually compiled into your SDL build determines whether the typical Direct3D‑first or OpenGL‑first order applies, and thus which driver will be selected when no hint is given.