Add the renderer process

The renderer becomes two programs: the adapter (t5deRenderEngine.dll, 32-bit, in IMVU's process) and a 64-bit renderer process (t5de-renderer.exe) drawing with Diligent Engine, fetched with FetchContent and pinned. For now a spike: the adapter starts the renderer process for each engine and signals each frame through a shared memory channel, and the renderer process draws a box into a child window in the client's 3D view.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

adapter/plugin.cpp

@@ -0,0 +1,59 @@
+// The renderer plugin's entry points, which SceneWindow.dll's createDLLRenderer looks up by name (exported
+// undecorated by plugin.def). For now the renderer is the pass-through: IMVU's Direct3D engine, wrapped.
+
+#include <windows.h>
+
+#include <exception>
+
+#include "log.hpp"
+#include "passthrough_engine.hpp"
+#include "renderer_process.hpp"
+#include "t5de/imvu/render_engine.hpp"
+
+namespace {
+
+using namespace t5de;
+
+// IMVU's Direct3D 9 engine, made by SceneWindow.dll (already loaded: it's what loads this plugin). Direct3D
+// rather than IMVU's OpenGL engine, which needs a real graphics driver: Direct3D also works on Windows' basic
+// display driver (virtual machines), and it's what most players use.
+imvu::SharedPtr<imvu::PiRenderEngine> create_imvu_engine(imvu::SharedPtr<imvu::INativeWindow> window)
+{
+    HMODULE scene_window = GetModuleHandleW(L"SceneWindow.dll");
+    auto create = scene_window == nullptr
+                      ? nullptr
+                      : reinterpret_cast<imvu::CreateRenderer>(GetProcAddress(scene_window, imvu::createRendererName));
+    if (create == nullptr) {
+        log::info("SceneWindow.dll's createRenderer not found");
+        return {};
+    }
+    return create(std::move(window), imvu::RendererType::Direct3D);
+}
+
+} // namespace
+
+extern "C" int __cdecl isRenderEngineSupported() { return 1; }
+
+// Returns a C++ object from a C-linkage function: fine here, the caller is C++ built for the same ABI.
+#pragma warning(suppress : 4190)
+extern "C" imvu::SharedPtr<imvu::PiRenderEngine> __cdecl createRenderEngine(imvu::SharedPtr<imvu::INativeWindow> window)
+{
+    try {
+        log::info("createRenderEngine: window {}", static_cast<void*>(window.get()));
+        HWND hwnd = window ? window->getPlatformWindow() : nullptr;
+        auto inner = create_imvu_engine(std::move(window));
+        if (!inner) {
+            return {};
+        }
+        auto renderer = hwnd != nullptr ? RendererProcess::start(hwnd) : nullptr;
+        return imvu::SharedPtr<imvu::PiRenderEngine>(
+            std::make_unique<PassthroughEngine>(std::move(inner), std::move(renderer)));
+    } catch (const std::exception& e) {
+        // Exceptions mustn't cross into IMVU's code (a different C++ runtime).
+        log::info("createRenderEngine failed: {}", e.what());
+        return {};
+    } catch (...) {
+        log::info("createRenderEngine failed");
+        return {};
+    }
+}