DXMT: keep indexed draw base vertex signed

[moreaki]

Problem

The DXMT indexed draw path currently carries the indexed draw base vertex through unsigned fields.

D3D11's BaseVertexLocation is signed, and Metal's baseVertex argument is signed as well. Negative base vertices are legal. Reinterpreting the value through uint32_t can turn a valid negative base vertex into a very large positive offset before the command reaches the winemetal encoder.

Proposed fix

Keep the base vertex signed across the DXMT/winemetal command boundary:

• DXMT_DRAW_INDEXED_ARGUMENTS::BaseVertex
• wmtcmd_render_draw_indexed::base_vertex

Validation

• git diff --check passed.
• This patch was cherry-picked on top of DXMT: add LLVM build compatibility fixes #748 and kmk VBoxDxMt completed successfully on macOS/Arm with LLVM 15.0.7.

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