Move Win32 async context ownership and trim canvas draw setup

src/platform_windows/windows_platform_services.cpp

@@ -26,6 +26,84 @@ void win32_update_stylus(float dt);
 void win32_save_window_state();
 bool win32_vr_start();
 void win32_vr_stop();
+std::string GetLastErrorAsString();
+
+namespace pp::platform::windows {
+
+namespace {
+
+struct RetainedWin32AsyncRenderContextState final {
+    HDC hdc{};
+    HGLRC hrc{};
+    std::mutex gl_mutex;
+    std::thread::id gl_thread{};
+    int gl_count = 0;
+};
+
+[[nodiscard]] RetainedWin32AsyncRenderContextState& retained_win32_async_render_context_state()
+{
+    static RetainedWin32AsyncRenderContextState state;
+    return state;
+}
+
+}
+
+void set_async_render_context(HDC hdc, HGLRC hrc)
+{
+    auto& state = retained_win32_async_render_context_state();
+    state.hdc = hdc;
+    state.hrc = hrc;
+    state.gl_thread = {};
+    state.gl_count = 0;
+}
+
+void lock_async_render_context()
+{
+    auto& state = retained_win32_async_render_context_state();
+    if (state.gl_count == 0 || state.gl_thread != std::this_thread::get_id())
+    {
+        state.gl_mutex.lock();
+        const bool ret = wglMakeCurrent(state.hdc, state.hrc);
+        if (!ret)
+            LOG("FAILED wglMakeCurrent: %s", GetLastErrorAsString().c_str());
+        state.gl_thread = std::this_thread::get_id();
+    }
+    state.gl_count++;
+}
+
+bool try_lock_async_render_context()
+{
+    auto& state = retained_win32_async_render_context_state();
+    if (state.gl_count == 0 || state.gl_thread != std::this_thread::get_id())
+    {
+        if (!state.gl_mutex.try_lock())
+            return false;
+        const bool ret = wglMakeCurrent(state.hdc, state.hrc);
+        if (!ret)
+            LOG("FAILED wglMakeCurrent: %s", GetLastErrorAsString().c_str());
+        state.gl_thread = std::this_thread::get_id();
+    }
+    state.gl_count++;
+    return true;
+}
+
+void unlock_async_render_context()
+{
+    auto& state = retained_win32_async_render_context_state();
+    state.gl_count--;
+    if (state.gl_count == 0)
+    {
+        wglMakeCurrent(0, 0);
+        state.gl_mutex.unlock();
+    }
+}
+
+void swap_async_render_context()
+{
+    SwapBuffers(retained_win32_async_render_context_state().hdc);
+}
+
+}
 
 namespace {