DXMT: keep indexed draw base vertex signed

[moreaki]

Problem

The bundled DXMT indexed-draw path carries the signed D3D base vertex through two unsigned command fields:

• DXMT_DRAW_INDEXED_ARGUMENTS::BaseVertex
• wmtcmd_render_draw_indexed::base_vertex

D3D11's BaseVertexLocation and Metal's indexed-draw baseVertex argument are both signed; negative base vertices are valid.

Deterministic reproduction

Use BaseVertexLocation = -1 in DrawIndexed or DrawIndexedInstanced.

The D3D11 entry point receives signed -1, but the current intermediate fields store 0xffffffff. When the winemetal field is passed to Metal's signed baseVertex parameter, it is promoted as positive 4294967295 rather than -1.

Minimal fix

Change only the two intermediate fields from uint32_t to int32_t. Both types are 32 bits, so the command layout is unchanged while signed promotion is restored.

PR: #758

Validation

• Reproduced by following the exact source path on current origin/main (5ac81eda).
• git diff --check passes.
• kmk VBoxDxMt succeeds with LLVM 15.0.7 on top of the build prerequisite in DXMT: fix the supported LLVM 15 build #748.
• The clean integrated macOS/Arm full build completes and produces VBoxDxMt.dylib.

Signed-off-by: Roberto Nibali rnibali@gmail.com