wgpu: fix the crash on Wayland sessions

[alpakaDurumi]

Each SDL_VIDEO_DRIVER_* macro is defined for every driver SDL was built with, so on Linux X11 and Wayland can be enabled at the same time. The surface source was chosen by an #elif chain on those macros, so a session actually running on Wayland could still be compiled into the X11 branch and set up the wrong surface source. It then read SDL_SysWMinfo.info.x11 out of a union holding Wayland members, handing a wl_display* to Xlib, which crashed in XGetXCBConnection() under wgpuInstanceRequestAdapter() (observed on Arch Linux with sdl2-compat as an SDL3 wrapper).

Check SDL_SysWMinfo.subsystem and set up the surface source from the driver actually in use.

[Copilot]

🟡 Changes recommended

The fix appears incomplete (similar logic remains in another code path) and the new switch has an unhandled default/invalid-chain scenario that can lead to undefined behavior.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR addresses a WebGPU surface-creation crash on Linux Wayland sessions by selecting the SDL native window handle source based on the runtime SDL_SysWMinfo.subsystem rather than a compile-time #elif chain over SDL_VIDEO_DRIVER_* macros.

Changes:

• Replaces compile-time #elif selection with a switch (windowWMInfo.subsystem) to choose the correct WGPUSurfaceSource*.
• Introduces a union-backed surfaceNativeDesc storage to hold the platform-specific WebGPU surface source descriptor.

File summaries

File	Description
src/Example.h	Switches WebGPU surface source selection to runtime SDL subsystem to avoid union misinterpretation on Wayland/X11 dual builds.

Review details

Suppressed comments (1)

src/Example.h:504

• surfaceDesc.nextInChain is currently set by casting the whole surfaceNativeDesc union to WGPUChainedStruct*. It’s safer and clearer to pass a pointer to the active surface-source struct’s .chain (all union members start at offset 0), avoiding type-punning a union object into an unrelated type.

        // create surface
        WGPUSurfaceDescriptor surfaceDesc{};
        surfaceDesc.nextInChain = (WGPUChainedStruct*)&surfaceNativeDesc;
        surfaceDesc.label.data = "The surface";

• Files reviewed: 1/1 changed files
• Comments generated: 2
• Review effort level: Lite

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