feat(ww3d2): add IRenderBackend Interface

[bobtista]

Summary

First PR in a planned multi-step refactor introducing an IRenderBackend interface in WW3D2. This PR adds only the scaffolding — interface, adapter, lifecycle wiring, and one isolated proof-of-concept call site. zero behavior change. The DX8 path remains the only renderer; g_renderBackend is constructed as a DX8Backend that forwards every method to the existing DX8Wrapper static facade.

What this PR adds

• IRenderBackend.h — abstract interface covering the W3D-facing subset of DX8Wrapper's public API. Only high-level methods (those taking ShaderClass/TextureBaseClass/Matrix4x4/etc.) are virtualized. D3D8-typed low-level methods stay on DX8Wrapper as DX8Backend-specific escape hatches — see the doc for the rationale.
• DX8Backend.{h,cpp} — concrete adapter that forwards every virtual method to the existing DX8Wrapper:: static functions. Pure forwarding, no new rendering logic.
• RenderBackend.{h,cpp} — exposes the global IRenderBackend* g_renderBackend. Init_Render_Backend() constructs new DX8Backend() from DX8Wrapper::Do_Onetime_Device_Dependent_Inits(); Shutdown_Render_Backend() tears it down from DX8Wrapper::Do_Onetime_Device_Dependent_Shutdowns().

Test plan

• Windows CI builds pass
• Game launches and runs a Skirmish round identically (no visual / behavioral difference)

[greptile-apps]

Greptile Summary

This PR introduces the IRenderBackend abstract interface, the DX8Backend concrete forwarding adapter, and the RenderBackend lifecycle owner as Phase 1 scaffolding for a multi-backend rendering refactor. Zero behavior changes: DX8Backend is a pure trampoline to the existing DX8Wrapper static API, and the global g_renderBackend is wired into the existing Do_Onetime_Device_Dependent_Inits/Shutdowns lifecycle hooks. The design choices (C++98 compatibility, TransformKind values mirroring D3DTS constants, opaque unsigned long shader handles) are all explicitly documented in the interface header.

Confidence Score: 5/5

Safe to merge — pure scaffolding with no behavior changes, correct lifecycle ordering, and thorough inline documentation.

All new files are clean, rule-compliant, and follow existing project conventions. No P0 or P1 findings. The interface design choices (C++98 compat, D3D-mirrored TransformKind values, opaque shader handles) are all intentional and well-documented. Lifecycle wiring into DX8Wrapper is minimal and correct.

No files require special attention.

Important Files Changed

Filename	Overview
Core/Libraries/Source/WWVegas/WW3D2/IRenderBackend.h	New abstract interface; clean forward-declaration strategy, documented C++98 constraints, #pragma once, GPL header, and nullptr-based destructor all correct.
Core/Libraries/Source/WWVegas/WW3D2/DX8Backend.h	Concrete adapter declaration; correctly inherits IRenderBackend, uses #pragma once, and mirrors the interface with virtual for C++98 compatibility.
Core/Libraries/Source/WWVegas/WW3D2/DX8Backend.cpp	Pure one-line trampolines to DX8Wrapper statics; Set_Viewport correctly converts RenderBackendViewport fields (types match D3DVIEWPORT8 exactly), shader handle casts to DWORD are safe on Windows.
Core/Libraries/Source/WWVegas/WW3D2/RenderBackend.h	Minimal accessor header; extern IRenderBackend * g_renderBackend declaration and two lifecycle function prototypes are correct, #pragma once and GPL header present.
Core/Libraries/Source/WWVegas/WW3D2/RenderBackend.cpp	Lifecycle management is correct; double-init guard and null-check on shutdown are both sound, nullptr used throughout.
Core/Libraries/Source/WWVegas/WW3D2/dx8wrapper.cpp	Adds Init_Render_Backend() at end of Do_Onetime_Device_Dependent_Inits and Shutdown_Render_Backend() at top of Do_Onetime_Device_Dependent_Shutdowns; ordering is correct to ensure backend is torn down before D3D device release.
Core/Libraries/Source/WWVegas/WW3D2/CMakeLists.txt	Adds all five new source/header files to WW3D2_SRC in alphabetically consistent positions.

Class Diagram

%%{init: {'theme': 'neutral'}}%%
classDiagram
    class IRenderBackend {
        <<abstract>>
        +Is_Device_Lost() bool
        +Has_Stencil() bool
        +Get_Back_Buffer_Format() WW3DFormat
        +Begin_Scene() void
        +End_Scene(flip_frame) void
        +Clear(...) void
        +Set_Viewport(viewport) void
        +Set_Shader(shader) void
        +Set_Texture(stage, texture) void
        +Set_Transform(kind, m) void
        +Set_Light(index, light) void
        +Draw_Triangles(...) void
        +Set_Vertex_Shader(vs) void
        +Create_Render_Target(...) TextureClass*
        +~IRenderBackend() void
    }

    class DX8Backend {
        +DX8Backend()
        +~DX8Backend()
        ... all IRenderBackend methods
    }

    class DX8Wrapper {
        <<static facade>>
        +Do_Onetime_Device_Dependent_Inits()$
        +Do_Onetime_Device_Dependent_Shutdowns()$
    }

    class RenderBackend {
        <<global owner>>
        +g_renderBackend IRenderBackend*
        +Init_Render_Backend() void
        +Shutdown_Render_Backend() void
    }

    IRenderBackend <|-- DX8Backend : implements
    DX8Backend --> DX8Wrapper : forwards all calls
    RenderBackend --> DX8Backend : constructs / owns
    DX8Wrapper --> RenderBackend : Init/Shutdown calls

Loading

_{Reviews (3): Last reviewed commit: "fix(ww3d2): Update copyright headers to ..." | Re-trigger Greptile}