Add an "offscreen" mode that allows users to render studio to a texture

then uses SDL to blit the texture into the window.

PiperOrigin-RevId: 861697047
Change-Id: Ib949b4ade0c79d867ba74ce013bc2b6fa2571f56

src/experimental/studio/app.cc

@@ -46,17 +46,16 @@
 
 namespace mujoco::studio {
 
-static constexpr platform::Window::Config kWindowConfig = {
+static constexpr platform::Window::RenderConfig kRenderConfig =
 #if defined(__EMSCRIPTEN__)
-    .render_config = platform::Window::RenderConfig::kFilamentWebGL,
+  platform::Window::RenderConfig::kFilamentWebGL;
 #elif defined(USE_FILAMENT_VULKAN)
-    .render_config = platform::Window::RenderConfig::kFilamentVulkan,
+  platform::Window::RenderConfig::kFilamentVulkan;
 #elif defined(USE_FILAMENT_OPENGL)
-    .render_config = platform::Window::RenderConfig::kFilamentOpenGL,
+  platform::Window::RenderConfig::kFilamentOpenGL;
 #elif defined(USE_CLASSIC_OPENGL)
-    .render_config = platform::Window::RenderConfig::kClassicOpenGL,
+  platform::Window::RenderConfig::kClassicOpenGL;
 #endif
-};
 
 static void ToggleFlag(mjtByte& flag) { flag = flag ? 0 : 1; }
 
@@ -113,10 +112,13 @@ static constexpr std::array<const char*, 31> kPercentRealTime = {
 };
 // clang-format on
 
-App::App(int width, int height, std::string ini_path)
-    : ini_path_(std::move(ini_path)) {
-  window_ = std::make_unique<platform::Window>("MuJoCo Studio", width, height,
-                                               kWindowConfig);
+App::App(Config config)
+    : ini_path_(std::move(config.ini_path)) {
+  platform::Window::Config window_config;
+  window_config.render_config = kRenderConfig;
+  window_config.offscreen_mode = config.offscreen_mode;
+  window_ = std::make_unique<platform::Window>("MuJoCo Studio", config.width,
+                                               config.height, window_config);
   renderer_ =
       std::make_unique<platform::Renderer>(window_->GetNativeWindowHandle());
 
@@ -428,11 +430,16 @@ void App::Render() {
   const float height = window_->GetHeight();
   const float scale = window_->GetScale();
 
+  if (window_->IsOffscreenMode()) {
+    pixels_.resize(width * height * 3);
+  } else {
+    pixels_.clear();
+  }
   renderer_->Render(model_, data_, &perturb_, &camera_, &vis_options_,
-                    width * scale, height * scale);
+                    width * scale, height * scale, pixels_);
 
   window_->EndFrame();
-  window_->Present();
+  window_->Present(pixels_);
 
   if (data_) {
     for (int i = 0; i < mjNTIMER; i++) {

src/experimental/studio/app.h

@@ -39,7 +39,22 @@ namespace mujoco::studio {
 // Owns, updates, and renders a MuJoCo simulation.
 class App {
  public:
-  App(int width, int height, std::string ini_path);
+  // Configuration/initialization options for the application.
+  struct Config {
+    // The original width and height of the window.
+    int width = 0;
+    int height = 0;
+
+    // The path to the ini file containing the user settings.
+    std::string ini_path;
+
+    // By default, we render directly to the window surface. However, in some
+    // cases, we may want to render to an (offscreen) texture and blit the
+    // texture to the window surface.
+    bool offscreen_mode = false;
+  };
+
+  explicit App(Config config);
 
   // Loads an empty mjModel.
   void InitEmptyModel();
@@ -211,6 +226,7 @@ class App {
   mjSpec* spec_ = nullptr;
   mjModel* model_ = nullptr;
   mjData* data_ = nullptr;
+  std::vector<std::byte> pixels_;
 
   mjvCamera camera_;
   mjvPerturb perturb_;

src/experimental/studio/main.cc

@@ -31,6 +31,7 @@
 ABSL_FLAG(int, window_width, 1400, "Window width");
 ABSL_FLAG(int, window_height, 720, "Window height");
 ABSL_FLAG(std::string, model_file, "", "MuJoCo model file.");
+ABSL_FLAG(bool, offscreen_mode, false, "Offscreen mode");
 
 std::string Resolve(std::string_view path) {
   std::string_view subpath = path.substr(path.find(':') + 1);
@@ -100,7 +101,13 @@ int main(int argc, char** argv, char** envp) {
 
   const int width = absl::GetFlag(FLAGS_window_width);
   const int height = absl::GetFlag(FLAGS_window_height);
-  mujoco::studio::App app(width, height, ini_path);
+  const bool offscreen_mode = absl::GetFlag(FLAGS_offscreen_mode);
+  mujoco::studio::App app({
+    .width = width,
+    .height = height,
+    .ini_path = ini_path,
+    .offscreen_mode = offscreen_mode,
+  });
 
   // If the model file is not specified, try to load it from the first argument
   std::string model_file = absl::GetFlag(FLAGS_model_file);

src/experimental/studio/wasm.cc

@@ -91,7 +91,11 @@ void Init() {
   resource_provider.prefix = "filament";
   mjp_registerResourceProvider(&resource_provider);
 
-  g_app = new mujoco::studio::App(width, height, ini_path);
+  g_app = new mujoco::studio::App({
+    .width = width,
+    .height = height,
+    .ini_path = ini_path,
+  });
   g_app->InitEmptyModel();
 }