Note the full view's speed on real hardware

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

.gitea/scripts/release.py

@@ -0,0 +1,152 @@
+"""Publish the renderer's programs. Run by ci.yml.
+
+    release.py version         print version and channel
+    release.py publish <dir>   publish the programs in dir: a release for a vX.Y.Z tag, else the rolling nightly
+
+A vX.Y.Z tag is release X.Y.Z. Other builds are nightlies, "X.Y.Z-nightly.N+commit": N commits after the last
+release tag (0.0.0 before the first). The nightly pre-release (tag `nightly`) is replaced on every push to main.
+The same scheme as T5DE's own releases (t5de's .gitea/scripts/release.py).
+"""
+
+import hashlib
+import json
+import os
+import re
+import subprocess
+import sys
+import urllib.error
+import urllib.request
+import uuid
+from pathlib import Path
+
+ASSETS = ("t5deRenderEngine.dll", "t5de-renderer.exe")
+NIGHTLY_TAG = "nightly"
+USER_AGENT = "t5de-release (https://git.t5de.dev/t5de/t5de-renderer, 1)"
+RELEASE_TAG = re.compile(r"v(\d+)\.(\d+)\.(\d+)")
+
+
+def git(*args: str) -> str:
+    return subprocess.run(["git", *args], capture_output=True, text=True, check=True).stdout.strip()
+
+
+def version() -> dict[str, str]:
+    ref_name = os.environ.get("GITHUB_REF_NAME", "")
+    if os.environ.get("GITHUB_REF_TYPE") == "tag" and RELEASE_TAG.fullmatch(ref_name):
+        return {"version": ref_name[1:], "channel": "release", "tag": ref_name}
+    try:
+        last = git("describe", "--tags", "--abbrev=0", "--match", "v[0-9]*.[0-9]*.[0-9]*")
+        count = int(git("rev-list", "--count", f"{last}..HEAD"))
+        base = last[1:]
+    except subprocess.CalledProcessError:  # no release yet
+        count, base = int(git("rev-list", "--count", "HEAD")), "0.0.0"
+    commit = git("rev-parse", "--short=7", "HEAD")
+    return {"version": f"{base}-nightly.{count}+{commit}", "channel": "nightly", "tag": NIGHTLY_TAG}
+
+
+class Gitea:
+    def __init__(self):
+        self.api = f"{os.environ['GITHUB_SERVER_URL']}/api/v1/repos/{os.environ['GITHUB_REPOSITORY']}"
+        self.token = os.environ["GITEA_TOKEN"]
+
+    def request(self, method: str, path: str, body: dict | None = None, data: bytes | None = None,
+                content_type: str = "application/json"):
+        if body is not None:
+            data = json.dumps(body).encode()
+        req = urllib.request.Request(self.api + path, method=method, data=data,
+                                     # Cloudflare in front of the server refuses Python's default User-Agent.
+                                     headers={"Authorization": f"token {self.token}", "Content-Type": content_type,
+                                              "User-Agent": USER_AGENT})
+        try:
+            with urllib.request.urlopen(req, timeout=120) as response:
+                text = response.read()
+                return json.loads(text) if text else None
+        except urllib.error.HTTPError as e:
+            if e.code == 404 and method in ("GET", "DELETE"):
+                return None
+            raise SystemExit(f"{method} {path}: {e.code} {e.read().decode(errors='replace')}")
+
+    def upload(self, release_id: int, name: str, content: bytes):
+        boundary = uuid.uuid4().hex
+        data = (f"--{boundary}\r\nContent-Disposition: form-data; name=\"attachment\"; filename=\"{name}\"\r\n"
+                f"Content-Type: application/octet-stream\r\n\r\n").encode() + content + f"\r\n--{boundary}--\r\n".encode()
+        return self.request("POST", f"/releases/{release_id}/assets?name={name}", data=data,
+                            content_type=f"multipart/form-data; boundary={boundary}")
+
+
+def notes(info: dict[str, str], files: dict[str, bytes]) -> str:
+    nightly = ("A nightly build of the latest commit, for testing; it's replaced by the next one.\n\n"
+               if info["channel"] == "nightly" else "")
+    hashes = "\n".join(f"`{name}` sha256: `{hashlib.sha256(content).hexdigest()}`" for name, content in files.items())
+    return f"""{nightly}T5DE's renderer for IMVU Classic: copy both files into a T5DE install's folder, and choose OpenGL
+in the client's Settings > Advanced (with T5DE's renderer patch).
+
+Unofficial: not made by or affiliated with IMVU. Use at your own risk.
+
+Version {info['version']} · commit {os.environ.get('GITHUB_SHA', git('rev-parse', 'HEAD'))}
+{hashes}
+"""
+
+
+def publish(folder: str):
+    info = version()
+    files = {name: (Path(folder) / name).read_bytes() for name in ASSETS}
+    gitea = Gitea()
+    previous = None
+    if info["channel"] == "nightly":
+        old = gitea.request("GET", f"/releases/tags/{NIGHTLY_TAG}")
+        if old:
+            previous = old["target_commitish"]
+            gitea.request("DELETE", f"/releases/{old['id']}")
+        gitea.request("DELETE", f"/tags/{NIGHTLY_TAG}")
+        release = gitea.request("POST", "/releases", {
+            "tag_name": NIGHTLY_TAG, "target_commitish": os.environ["GITHUB_SHA"],
+            "name": f"Nightly {info['version']}", "body": notes(info, files), "prerelease": True})
+    else:
+        release = gitea.request("GET", f"/releases/tags/{info['tag']}")
+        fields = {"name": f"T5DE Renderer {info['version']}", "body": notes(info, files), "prerelease": False}
+        if release:  # a rerun: refresh it
+            release = gitea.request("PATCH", f"/releases/{release['id']}", fields)
+            for asset in release.get("assets") or []:
+                if asset["name"] in files:
+                    gitea.request("DELETE", f"/releases/{release['id']}/assets/{asset['id']}")
+        else:
+            release = gitea.request("POST", "/releases", {"tag_name": info["tag"], **fields})
+    for name, content in files.items():
+        gitea.upload(release["id"], name, content)
+    print(f"Published {release['html_url']}")
+    if info["channel"] == "nightly" and os.environ.get("DISCORD_NIGHTLY_WEBHOOK"):
+        announce(os.environ["DISCORD_NIGHTLY_WEBHOOK"], info, release, previous)
+
+
+def announce(webhook: str, info: dict[str, str], release: dict, previous: str | None):
+    """Post the release to a Discord channel. Failing to doesn't fail the release."""
+    commits = []
+    if previous:
+        try:
+            commits = git("log", "--format=%h %s", "--no-merges", f"{previous}..HEAD").splitlines()
+        except subprocess.CalledProcessError:  # the previous nightly's commit is gone (history rewritten)
+            pass
+    shown = commits[:10] + ([f"and {len(commits) - 10} more"] if len(commits) > 10 else [])
+    description = f"[Download]({release['html_url']})"
+    if shown:
+        description += "\n\n" + "\n".join(f"• {line}" for line in shown)
+    body = {"embeds": [{"title": f"Renderer Nightly {info['version']}", "url": release["html_url"],
+                        "description": description[:4000], "color": 0xFFD200}]}
+    req = urllib.request.Request(webhook, method="POST", data=json.dumps(body).encode(),
+                                 headers={"Content-Type": "application/json",
+                                          "User-Agent": USER_AGENT})
+    try:
+        urllib.request.urlopen(req, timeout=30).close()
+        print("Announced on Discord")
+    except (urllib.error.URLError, TimeoutError) as e:
+        print(f"warning: couldn't post to Discord: {e}")
+
+
+if __name__ == "__main__":
+    if sys.argv[1:] == ["version"]:
+        for key, value in version().items():
+            print(f"{key}={value}")
+    elif len(sys.argv) == 3 and sys.argv[1] == "publish":
+        publish(sys.argv[2])
+    else:
+        raise SystemExit(__doc__)

.gitea/workflows/ci.yml

@@ -0,0 +1,59 @@
+# Builds the adapter (32-bit) and the renderer process (64-bit), runs the tests, and publishes both programs: pushes to
+# main replace the nightly pre-release, vX.Y.Z tags make release X.Y.Z (.gitea/scripts/release.py).
+#
+# Runs on T5DE's Windows runner (label `windows`, jobs run directly on the machine: it needs Visual Studio's
+# compiler). The checkout lives in a fixed folder there ($T5DE_BUILD_ROOT, set in the runner's config), so Diligent
+# Engine is fetched and built once, not on every run. Never on pull requests: their code would run on that machine.
+name: CI
+
+on:
+  push:
+    branches: [main]
+    tags: ["v*"]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: windows
+    defaults:
+      run:
+        # Steps run as script files, which Windows' default execution policy refuses.
+        shell: powershell -NoProfile -ExecutionPolicy Bypass -Command ". '{0}'"
+    steps:
+      - name: Check out
+        env:
+          TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          function git { & git.exe -c "http.extraHeader=Authorization: token $env:TOKEN" @args; if ($LASTEXITCODE) { exit $LASTEXITCODE } }
+          $root = if ($env:T5DE_BUILD_ROOT) { $env:T5DE_BUILD_ROOT } else { $env:GITHUB_WORKSPACE }
+          $src = Join-Path $root ($env:GITHUB_REPOSITORY -replace '/', '-')
+          if (-not (Test-Path (Join-Path $src .git))) { git init -q $src }
+          Set-Location $src
+          git fetch -q --force --tags "$env:GITHUB_SERVER_URL/$env:GITHUB_REPOSITORY" "+${env:GITHUB_REF}:refs/remotes/ci/head"
+          git checkout -q --force --detach $env:GITHUB_SHA
+          git clean -q -ffdx -e /build/
+          "T5DE_SRC=$src" | Out-File -Append -Encoding utf8 $env:GITHUB_ENV
+
+      - name: Build and test the adapter
+        working-directory: ${{ env.T5DE_SRC }}
+        run: cmake --workflow --preset adapter
+
+      - name: Build the renderer process
+        working-directory: ${{ env.T5DE_SRC }}
+        run: cmake --workflow --preset renderer
+
+      - name: Collect the programs
+        working-directory: ${{ env.T5DE_SRC }}
+        run: |
+          cmake --install build/windows-x86 --config Release --prefix dist
+          if ($LASTEXITCODE) { exit $LASTEXITCODE }
+          cmake --install build/windows-x64 --config Release --prefix dist
+
+      - name: Publish the release
+        if: github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/v')
+        working-directory: ${{ env.T5DE_SRC }}
+        env:
+          GITEA_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          # Optional: a Discord webhook URL that nightlies are announced on.
+          DISCORD_NIGHTLY_WEBHOOK: ${{ secrets.DISCORD_NIGHTLY_WEBHOOK }}
+        run: python .gitea/scripts/release.py publish dist

adapter/engine.cpp

@@ -47,7 +47,9 @@ void Engine::enable2dFrameBuffer() { inner_->enable2dFrameBuffer(); }
 
 void Engine::clear(std::uint32_t flags, imvu::Color color)
 {
+    if (innerDraws()) {
         inner_->clear(flags, color);
+    }
     recorder_->add(Op::Clear, protocol::Clear{flags, color});
 }
 
@@ -242,6 +244,13 @@ imvu::SharedPtr<imvu::PiTextureRenderTarget> Engine::newTextureRenderTarget(imvu
 void Engine::beginRendering(imvu::PiRenderTarget* target)
 {
     inner_->beginRendering(target);
+    // Decided per frame: frames into render targets, and frames while the renderer process doesn't cover the view, are
+    // drawn by the client's renderer.
+    const bool takenOver = target == nullptr && recorder_->covering();
+    if (takenOver != takenOver_ && target == nullptr) {
+        log::info("engine: frame {}: {}", frames_, takenOver ? "drawn by the renderer process" : "drawn by the client's renderer");
+    }
+    takenOver_ = takenOver;
     if (target != nullptr && foreignLogged_ < 20) {
         ++foreignLogged_;
         log::info("engine: frame {}: drawing into a render target ({})", frames_, static_cast<void*>(target));
@@ -271,7 +280,9 @@ void Engine::drawTriangles(imvu::PiInternalIndexBuffer* indices, imvu::PiInterna
                            imvu::PiInternalVertexBuffer* normals, imvu::PiInternalVertexBuffer* texCoords,
                            imvu::PiInternalVertexBuffer* colors)
 {
+    if (innerDraws()) {
         inner_->drawTriangles(inner(indices), inner(positions), inner(normals), inner(texCoords), inner(colors));
+    }
     ++(id(indices) != 0 && id(positions) != 0 ? stats_.triangles : stats_.foreignTriangles);
     recorder_->add(Op::DrawTriangles,
                    protocol::DrawTriangles{id(indices), id(positions), id(normals), id(texCoords), id(colors)});
@@ -279,13 +290,17 @@ void Engine::drawTriangles(imvu::PiInternalIndexBuffer* indices, imvu::PiInterna
 
 void Engine::drawLine(imvu::Vec3f from, imvu::Vec3f to, imvu::Color color)
 {
+    if (innerDraws()) {
         inner_->drawLine(from, to, color);
+    }
     ++stats_.lines;
 }
 
 void Engine::drawPointSprites(const imvu::PointSpriteVector& sprites)
 {
+    if (innerDraws()) {
         inner_->drawPointSprites(sprites);
+    }
     ++stats_.sprites;
     if (sprites.first == nullptr || sprites.last <= sprites.first) {
         return;
@@ -304,7 +319,9 @@ void Engine::drawTrianglesFromMemory(std::uint32_t vertexCount, std::uint32_t in
                                      const imvu::VertexAttributeArray<imvu::Vec2f>& texCoords,
                                      const imvu::VertexAttributeArray<imvu::Color>& colors)
 {
+    if (innerDraws()) {
         inner_->drawTrianglesFromMemory(vertexCount, indexCount, indices, positions, normals, texCoords, colors);
+    }
     ++(indices != nullptr ? stats_.indexed : stats_.unindexed);
     if (positions.data == nullptr || vertexCount == 0) {
         return;

adapter/engine.hpp

@@ -1,7 +1,10 @@
 #pragma once
-// The adapter's engine: what the client draws with. Everything goes to the client's own Direct3D renderer, which
-// still draws the whole 3D view, and is recorded for the renderer process, which draws its part on top (the right
-// half for now, to compare). If the renderer process fails, the client's renderer carries on alone.
+// The adapter's engine: what the client draws with. Everything is recorded for the renderer process, which draws the
+// 3D view. The client's own Direct3D renderer gets everything too (state and resources: it still draws into render
+// targets and reads textures back, which the renderer process doesn't yet), but while the renderer process covers the
+// whole view, the client's renderer skips its frames' clears and draws. When the renderer process doesn't cover it
+// (it failed, or shows only part of the view, for comparing) the client's renderer draws everything, from the next
+// frame on.
 
 #include <cstdint>
 #include <memory>
@@ -63,10 +66,13 @@ public:
 
 private:
     void setState(protocol::State state, std::uint32_t value);
+    // Whether the client's renderer should draw this frame's clears and draws.
+    [[nodiscard]] bool innerDraws() const { return !takenOver_; }
 
     imvu::SharedPtr<imvu::PiRenderEngine> inner_;
     std::shared_ptr<Recorder> recorder_;
     std::uint64_t frames_ = 0;
+    bool takenOver_ = false; // this frame is drawn by the renderer process only
     int foreignLogged_ = 0; // diagnostics: textures the client renderer made, render targets
 
     // Diagnostics: what the client draws, summed over 300 frames and logged (the first few times).

adapter/plugin.cpp

@@ -33,7 +33,7 @@ imvu::SharedPtr<imvu::PiRenderEngine> create_imvu_engine(imvu::SharedPtr<imvu::I
     return create(std::move(window), imvu::RendererType::Direct3D);
 }
 
-// What the renderer process draws: T5DE_RENDERER_VIEW=off, split (the default: the right half), full or compare.
+// What the renderer process draws: T5DE_RENDERER_VIEW=off, split (the right half), full (the default) or compare.
 // (The renderer process can also be switched while it runs: renderer/main.cpp.)
 protocol::View view()
 {
@@ -41,9 +41,9 @@ protocol::View view()
     GetEnvironmentVariableW(L"T5DE_RENDERER_VIEW", value, 16);
     const std::wstring_view setting = value;
     return setting == L"off"       ? protocol::View::Off
-           : setting == L"full"    ? protocol::View::Full
+           : setting == L"split"   ? protocol::View::Split
            : setting == L"compare" ? protocol::View::Compare
-                                   : protocol::View::Split;
+                                   : protocol::View::Full;
 }
 
 } // namespace

adapter/recorder.hpp

@@ -18,6 +18,9 @@ public:
 
     [[nodiscard]] bool active() const { return process_ && process_->alive(); }
 
+    // Whether the renderer process draws the whole 3D view, so the client's renderer needn't.
+    [[nodiscard]] bool covering() const { return process_ && process_->covering(); }
+
     // Records a command (if active); returns its payload to fill, or null.
     template <class Body>
     std::byte* add(protocol::Op op, const Body& body, std::size_t payloadSize = 0)

adapter/renderer_process.cpp

@@ -84,11 +84,15 @@ std::unique_ptr<RendererProcess> RendererProcess::start(HWND window, protocol::V
                            .view = view,
                            .capacity = protocol::channelCapacity,
                            .chunkSize = 0,
-                           .chunkFlags = 0};
-
-    // The renderer's window goes on top of the client's 3D view: keep the client's drawing out of it.
-    SetWindowLongW(window, GWL_STYLE, GetWindowLongW(window, GWL_STYLE) | WS_CLIPCHILDREN);
+                           .chunkFlags = 0,
+                           .covering = 0,
+                           .reserved = 0};
 
+    // The renderer's window goes on top of the client's 3D view, as a child window. The client's window mustn't clip
+    // its children (WS_CLIPCHILDREN, which the client creates it with): the client draws a frame when its window gets
+    // WM_PAINT, which a window entirely covered by clipped children never gets (it then drew about once a second). The
+    // renderer's swap chain is a flip model one, which the compositor shows above the client's drawing anyway.
+    SetWindowLongW(window, GWL_STYLE, GetWindowLongW(window, GWL_STYLE) & ~WS_CLIPCHILDREN);
     const auto exe = running_copy(module_folder() / L"t5de-renderer.exe");
     std::wstring command = std::format(L"\"{}\" --channel {} --parent {}", exe.wstring(), name, GetCurrentProcessId());
     STARTUPINFOW startup{.cb = sizeof(STARTUPINFOW)};

adapter/renderer_process.hpp

@@ -27,6 +27,9 @@ public:
 
     [[nodiscard]] bool alive() const { return alive_; }
 
+    // Whether the renderer process covers the whole 3D view (protocol::Channel::covering).
+    [[nodiscard]] bool covering() const { return alive_ && channel_->covering != 0; }
+
 private:
     RendererProcess() = default;
 

docs/architecture.md

@@ -29,19 +29,26 @@ creates (each 3D view, and again on room changes), the adapter:
 
 The renderer process draws into a child window it creates inside the client's window: window handles are valid in
 every process, and Windows allows child windows across processes (Chrome's GPU process works this way). The child
-is disabled so mouse input goes to the client's window under it, and the adapter gives the client's window
-`WS_CLIPCHILDREN` so the client's own drawing stays out of it. The process exits when the engine is destroyed or the
-client exits.
+is disabled so mouse input goes to the client's window under it. Its swap chain is a flip model one, which the
+compositor shows above the client's own drawing. The client's window must not clip its children (`WS_CLIPCHILDREN`,
+which the client creates it with, so the adapter clears it):
+the client draws a frame when its window gets `WM_PAINT` (`SceneWindow.dll` invalidates it, and draws on the paint),
+and a window entirely covered by clipped children never gets one, so the client fell to about one frame a second.
+The process exits when the engine is destroyed or the client exits.
 
 ## Status
 
-The renderer process draws the client's whole scene, over the right half of the 3D view, beside the client's own
-Direct3D renderer on the left (the adapter still forwards everything to it). Checked in rooms with screenshots of
-both renderers side by side (the compare view): they match, particles and the 2D overlay (name tags) included.
+The renderer process draws the whole 3D view in place of the client's renderer (the full view, the default). The
+adapter still forwards everything to the client's Direct3D renderer (state and resources: it draws render targets and
+reads textures back, which the renderer process doesn't yet), but while the renderer process covers the whole view
+(`Channel::covering`, set after each frame it presents) the client's renderer skips its clears and draws, decided per
+frame; it draws again as soon as the renderer process stops covering the view (the view changes, or the process
+fails). Checked in rooms with screenshots of both renderers side by side (the compare view): they match, particles
+and the 2D overlay (name tags) included.
 
 For comparing while the client runs (development):
 
-- Views: `T5DE_RENDERER_VIEW` (off, split, full or compare) when the client starts, or
+- Views: `T5DE_RENDERER_VIEW` (off, split, full (the default) or compare) when the client starts, or
   `%TEMP%\t5de-renderer-view.txt` holding one of those at any time. Compare draws the left half's scene over the
   right half, so both renderers show the same thing side by side.
 - `%TEMP%\t5de-renderer-shaders\fixed_function.hlsl`, if present, replaces the built-in shaders and is reloaded
@@ -57,14 +64,14 @@ For comparing while the client runs (development):
   be taken, and gives up on a renderer process that stops taking them (the client's renderer carries on).
 - The renderer process reproduces IMVU's Direct3D 9 setup (`renderer/shaders/fixed_function.hlsl`), particles
   included (point sprites, drawn as instanced squares), with a pipeline per combination of states.
-- Speed: on the development VM (software rendering) a room frame takes 8 to 60 ms to draw; the time from the
-  client finishing a frame to ours being presented averages about 60 ms. The renderer process draws only the
-  newest frame when it falls behind, and keeps at most one frame queued. Over Remote Desktop, the half drawn by the
-  renderer process (another process's window, composited by Windows) visibly trails the client's half by more
-  than that; that delay comes after presenting, and is to be checked on a real graphics card and display.
+- Speed: on a PC with a graphics card, drawing the whole view (3440x1059, a room of some 220 draws) takes 1.3 to
+  3.8 ms a frame, and the time from the client finishing a frame to ours being presented is the same (frames don't
+  queue, none skipped). Earlier, in the split view, the halves couldn't be told apart, even while the camera moved. On the development VM (software rendering, over Remote Desktop) drawing takes 8 to 60 ms, and
+  the right half visibly trails, mostly from compositing another process's window over Remote Desktop. The
+  renderer process draws only the newest frame when it falls behind, and keeps at most one frame queued.
 
-Next: render targets (offscreen frames are skipped), the renderer process drawing the whole view in place of the
-client's renderer, and one renderer process for all of a client's views.
+Next: render targets (offscreen frames are skipped, and drawn by the client's renderer), and one renderer process for
+all of a client's views.
 
 ## Building
 

include/t5de/protocol/channel.hpp

@@ -7,9 +7,10 @@
 
 namespace t5de::protocol {
 
-inline constexpr std::uint32_t version = 2;
+inline constexpr std::uint32_t version = 3;
 
-// Which part of the client's 3D view the renderer process draws (the client's own renderer draws all of it, under).
+// Which part of the client's 3D view the renderer process draws. Full is the default; the others are for comparing
+// with the client's renderer, which then draws the whole view under the renderer process's window.
 enum class View : std::uint32_t {
     Off,     // none
     Split,   // the right half, to compare with the client's renderer on the left
@@ -30,9 +31,13 @@ struct Channel {
     std::uint32_t capacity;
     std::uint32_t chunkSize;
     std::uint32_t chunkFlags; // chunkEndsFrame
+    // Set by the renderer process while its window covers the whole 3D view and it's presenting frames: the client's
+    // renderer then needn't draw (the adapter skips its draws; it draws again as soon as this is cleared).
+    std::uint32_t covering;
+    std::uint32_t reserved;
 };
 
-static_assert(sizeof(Channel) == 40, "same layout in 32-bit and 64-bit builds");
+static_assert(sizeof(Channel) == 48, "same layout in 32-bit and 64-bit builds");
 
 inline constexpr std::uint32_t chunkEndsFrame = 1;
 inline constexpr std::uint32_t channelCapacity = 16 * 1024 * 1024;

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;