Draw the whole 3D view in place of the client's renderer

The full view is now the default. While the renderer process covers the whole
view (Channel::covering, set after each frame it presents), the adapter skips
the client's renderer's clears and draws, decided per frame; the client's
renderer still gets state and resources, and draws again as soon as the
renderer process stops covering the view.

The client's window no longer gets WS_CLIPCHILDREN: the client draws when its
window gets WM_PAINT, which a window entirely covered by clipped children never
gets (it fell to about one frame a second). The flip model swap chain shows
above the client's drawing anyway.

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

renderer/main.cpp

@@ -290,14 +290,17 @@ int WINAPI wWinMain(HINSTANCE, HINSTANCE, PWSTR, int)
                 info("drawing {}x{} at {} in the client's 3D view, its scene from {}", width, height, place.left, offset);
             } else {
                 ShowWindow(window, SW_HIDE);
+                channel->covering = 0;
                 info("hidden");
             }
         }
         reload_shaders(scene);
         LARGE_INTEGER start, end;
         QueryPerformanceCounter(&start);
+        const bool covers = current_view(channel->view) == View::Full && width > 0 && height > 0;
         if (scene.execute(std::span(frame).first(complete), offset, width > 0 && height > 0)) {
             swapChain->Present(0);
+            channel->covering = covers ? 1 : 0; // the client's renderer can stop drawing (or must start again)
             QueryPerformanceCounter(&end);
             drawTime += static_cast<double>(end.QuadPart - start.QuadPart) / static_cast<double>(frequency.QuadPart);
             latency += static_cast<double>(end.QuadPart - static_cast<LONGLONG>(scene.lastSentAt())) /
@@ -315,6 +318,7 @@ int WINAPI wWinMain(HINSTANCE, HINSTANCE, PWSTR, int)
         frame.erase(frame.begin(), frame.begin() + static_cast<std::ptrdiff_t>(complete));
     }
 
+    channel->covering = 0;
     info("exiting");
     DestroyWindow(window);
     return 0;