Use runtime enum for the renderer backend instead of preprocessor macros.

TESTED:
  studio:vulkan
  studio:vulkan --offscreen_mode=true
  studio:opengl
  studio:opengl_egl
  studio:classic
  studio:classic --offscreen_mode=true
  studio:server
  robot_sim/frontend:debug_server
  pyviewer:example
  pyviewer:example --define=mujoco_gl=vulkan
PiperOrigin-RevId: 864768322
Change-Id: I4478e0115b3807060d60d98b4ddfd63da9389aac

src/experimental/platform/CMakeLists.txt

@@ -18,13 +18,13 @@ set(MUJOCO_PLATFORM_TARGET_NAME mujoco_platform)
 
 # Determine the render configuration and dependencies based options.
 if(MUJOCO_USE_FILAMENT AND MUJOCO_USE_FILAMENT_VULKAN)
-    set(MUJOCO_PLATFORM_RENDER_CONFIG "USE_FILAMENT_VULKAN")
+    set(MUJOCO_PLATFORM_RENDER_CONFIG "MUJOCO_RENDERER_FILAMENT_VULKAN")
     set(MUJOCO_PLATFORM_RENDER_DEPS "mujoco::filament")
 elseif(MUJOCO_USE_FILAMENT)
-    set(MUJOCO_PLATFORM_RENDER_CONFIG "USE_FILAMENT_OPENGL")
+    set(MUJOCO_PLATFORM_RENDER_CONFIG "MUJOCO_RENDERER_FILAMENT_OPENGL")
     set(MUJOCO_PLATFORM_RENDER_DEPS "mujoco::filament")
 else()
-    set(MUJOCO_PLATFORM_RENDER_CONFIG "USE_CLASSIC_OPENGL")
+    set(MUJOCO_PLATFORM_RENDER_CONFIG "MUJOCO_RENDERER_CLASSIC_OPENGL")
     set(MUJOCO_PLATFORM_RENDER_DEPS "dear_imgui_OpenGL3")
 endif()
 
@@ -52,6 +52,7 @@ target_sources(${MUJOCO_PLATFORM_TARGET_NAME}
         plugin.h
         renderer.cc
         renderer.h
+        renderer_backend.h
         sim_history.cc
         sim_history.h
         sim_profiler.cc

src/experimental/platform/renderer.cc

@@ -18,21 +18,20 @@
 #include <span>
 
 #include <mujoco/mujoco.h>
+#include "experimental/platform/renderer_backend.h"
 
-#if defined(USE_FILAMENT_OPENGL) || defined(USE_FILAMENT_VULKAN)
-#include "experimental/filament/render_context_filament.h"
-#include "experimental/platform/plugin.h"
-#elif defined(USE_CLASSIC_OPENGL)
+#if defined(MUJOCO_RENDERER_CLASSIC_OPENGL)
 #include <imgui.h>
 #include <backends/imgui_impl_opengl3.h>
 #else
-#error No rendering mode defined.
+#include "experimental/filament/render_context_filament.h"
+#include "experimental/platform/plugin.h"
 #endif
 
 namespace mujoco::platform {
 
 Renderer::Renderer(void* native_window) : native_window_(native_window) {
-#ifdef USE_CLASSIC_OPENGL
+#ifdef MUJOCO_RENDERER_CLASSIC_OPENGL
   ImGui_ImplOpenGL3_Init();
 #endif
 }
@@ -44,16 +43,18 @@ void Renderer::Init(const mjModel* model) {
   if (model) {
     mjr_defaultContext(&render_context_);
 
-#if defined(USE_CLASSIC_OPENGL)
+#if defined(MUJOCO_RENDERER_CLASSIC_OPENGL)
     mjr_makeContext(model, &render_context_, mjFONTSCALE_150);
 #else
     mjrFilamentConfig render_config;
     mjr_defaultFilamentConfig(&render_config);
     render_config.native_window = native_window_;
     render_config.enable_gui = true;
-#if defined(USE_FILAMENT_OPENGL)
+#if defined(MUJOCO_RENDERER_FILAMENT_OPENGL)
     render_config.graphics_api = mjGFX_OPENGL;
-#elif defined(USE_FILAMENT_VULKAN)
+#elif defined(MUJOCO_RENDERER_FILAMENT_OPENGL_HEADLESS)
+    render_config.graphics_api = mjGFX_OPENGL;
+#elif defined(MUJOCO_RENDERER_FILAMENT_VULKAN)
     render_config.graphics_api = mjGFX_VULKAN;
 #endif
     mjr_makeFilamentContext(model, &render_context_, &render_config);
@@ -92,7 +93,7 @@ void Renderer::Render(const mjModel* model, mjData* data,
                 width * height * 3);
     }
 
-    #ifdef USE_CLASSIC_OPENGL
+    #ifdef MUJOCO_RENDERER_CLASSIC_OPENGL
       mjr_resizeOffscreen(width, height, &render_context_);
       mjr_setBuffer(mjFB_OFFSCREEN, &render_context_);
     #else
@@ -108,7 +109,7 @@ void Renderer::Render(const mjModel* model, mjData* data,
 
   // The filament backend knows how to renders the ImGui draw data. For the
   // classic backend, we need to render the ImGui draw data ourselves.
-  #ifdef USE_CLASSIC_OPENGL
+  #ifdef MUJOCO_RENDERER_CLASSIC_OPENGL
     ImGui_ImplOpenGL3_NewFrame();
     ImGui::Render();
     ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
@@ -141,7 +142,7 @@ void Renderer::RenderToTexture(const mjModel* model, mjData* data,
 
 int Renderer::UploadImage(int texture_id, const std::byte* pixels, int width,
                           int height, int bpp) {
-#if defined(USE_CLASSIC_OPENGL)
+#if defined(MUJOCO_RENDERER_CLASSIC_OPENGL)
   return 0;
 #else
   return mjr_uploadGuiImage(texture_id,
@@ -153,7 +154,7 @@ int Renderer::UploadImage(int texture_id, const std::byte* pixels, int width,
 double Renderer::GetFps() { return fps_; }
 
 void Renderer::UpdateFps() {
-#ifdef USE_CLASSIC_OPENGL
+#ifdef MUJOCO_RENDERER_CLASSIC_OPENGL
   TimePoint now = std::chrono::steady_clock::now();
   TimePoint::duration delta_time = now - last_fps_update_;
   const double interval = std::chrono::duration<double>(delta_time).count();
@@ -168,9 +169,25 @@ void Renderer::UpdateFps() {
 #endif
 }
 
+RendererBackend Renderer::GetBackend() {
+#if defined(MUJOCO_RENDERER_FILAMENT_OPENGL_HEADLESS)
+  return RendererBackend::FilamentOpenGlHeadless;
+#elif defined(MUJOCO_RENDERER_FILAMENT_OPENGL)
+  return RendererBackend::FilamentOpenGl;
+#elif defined(MUJOCO_RENDERER_FILAMENT_VULKAN)
+  return RendererBackend::FilamentVulkan;
+#elif defined(MUJOCO_RENDERER_FILAMENT_WEBGL)
+  return RendererBackend::FilamentWebGl;
+#elif defined(MUJOCO_RENDERER_CLASSIC_OPENGL)
+  return RendererBackend::ClassicOpenGl;
+#else
+  #error "Unsupported renderer backend."
+#endif
+}
+
 }  // namespace mujoco::platform
 
-#if !defined(USE_CLASSIC_OPENGL)
+#if !defined(MUJOCO_RENDERER_CLASSIC_OPENGL)
 mjPLUGIN_LIB_INIT {
   mujoco::platform::GuiPlugin plugin;
   plugin.name = "Filament";

src/experimental/platform/renderer.h

@@ -21,11 +21,33 @@
 #include <span>
 
 #include <mujoco/mujoco.h>
+#include "experimental/platform/renderer_backend.h"
 
 namespace mujoco::platform {
 
-// Renders the mujoco simulation and the imgui state into the active window
-// using the filament rendering backend.
+// Renders the mujoco simulation and the imgui state.
+//
+// The Renderer is built around a specific backend configuration
+// (see renderer_backend.h).
+//
+// Currently we support two rendering engines: the Classic MuJoCo OpenGL
+// renderer and a Filament-based renderer.
+//
+// The Classic renderer is implemented using the OpenGL 2.0 fixed function
+// pipeline. It assumes that the caller has correctly initialized the OpenGL
+// context (e.g. using EGL).
+//
+// The Filament renderer is a modern physically-based renderer that supports
+// OpenGL 3.0, Vulkan, and WebGL (as well as other graphics libraries). Unlike
+// the Classic renderer, the Filament engine itself will manage its graphics
+// context. If rendering to a window surface (e.g. x11), it requires a pointer
+// to the native window to do so.
+//
+// For OpenGL, two different Filament configurations are available: normal and
+// headless. Normal rendering assumes that we will be rendering to an x11
+// window and therefore will use a x11-based context. Headless assumes that we
+// will be rendering to a texture and will use an EGL context. Vulkan and WebGL
+// have no need for such a distinction.
 class Renderer {
  public:
   using Clock = std::chrono::steady_clock;
@@ -66,6 +88,10 @@ class Renderer {
   // Returns the current frame rate.
   double GetFps();
 
+  // Returns the statically-defined backend for which this renderer is
+  // configured.
+  static RendererBackend GetBackend();
+
  private:
   // Resets the renderer; no rendering will occur until Init() is called again.
   void Deinit();

src/experimental/platform/renderer_backend.h

@@ -0,0 +1,47 @@
+// Copyright 2026 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef MUJOCO_SRC_EXPERIMENTAL_PLATFORM_RENDERER_BACKEND_H_
+#define MUJOCO_SRC_EXPERIMENTAL_PLATFORM_RENDERER_BACKEND_H_
+
+namespace mujoco::platform {
+
+// Describes the configuration of the renderer backend.
+//
+// This is generally a combination of two things. The first describes the
+// high-level rendering engine that sits behind the MuJoCo API (e.g.
+// mjr_render). The second describes the low-level graphics engine that is
+// powering the rendering (e.g. OpenGL, Vulkan, etc.).
+//
+// More details about the backends can be found in renderer.h.
+enum class RendererBackend {
+  // The classic MuJoCo OpenGL renderer.
+  ClassicOpenGl,
+
+  // The Filament-based renderer running on OpenGL.
+  FilamentOpenGl,
+
+  // The Filament-based renderer running on Vulkan.
+  FilamentVulkan,
+
+  // The Filament-based renderer running on WebGL.
+  FilamentWebGl,
+
+  // Similar to FilamentOpenGl, but assumes "headless" rendering.
+  FilamentOpenGlHeadless,
+};
+
+}  // namespace mujoco::platform
+
+#endif  // MUJOCO_SRC_EXPERIMENTAL_PLATFORM_RENDERER_BACKEND_H_

src/experimental/platform/window.cc

@@ -36,6 +36,7 @@
 #include <backends/imgui_impl_sdl2.h>
 #include <imgui.h>
 #include <mujoco/mujoco.h>
+#include "experimental/platform/renderer_backend.h"
 #include "user/user_resource.h"
 
 // Because X11/Xlib.h defines Status.
@@ -98,7 +99,11 @@ static void InitImGui(SDL_Window* window, float content_scale, bool load_fonts,
 
 Window::Window(std::string_view title, int width, int height, Config config)
     : width_(width), height_(height), config_(config) {
-  const RenderConfig render_config = config_.render_config;
+  const RendererBackend renderer_backend = config_.renderer_backend;
+  if (renderer_backend == RendererBackend::FilamentOpenGlHeadless) {
+    config_.offscreen_mode = true;
+  }
+
   if (config_.offscreen_mode) {
     SDL_SetHint(SDL_HINT_RENDER_DRIVER, "software");
     SDL_SetHint(SDL_HINT_FRAMEBUFFER_ACCELERATION, "0");
@@ -118,20 +123,21 @@ Window::Window(std::string_view title, int width, int height, Config config)
   }
 
   int window_flags = SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI;
-  if (render_config == kFilamentVulkan) {
+  if (renderer_backend == RendererBackend::FilamentVulkan) {
     window_flags |= SDL_WINDOW_VULKAN;
-  } else if (render_config == kFilamentWebGL) {
+  } else if (renderer_backend == RendererBackend::FilamentWebGl) {
     window_flags |= SDL_WINDOW_OPENGL;
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
-  } else if (render_config == kClassicOpenGL ||
-             render_config == kFilamentOpenGL) {
+  } else if (renderer_backend == RendererBackend::ClassicOpenGl ||
+             renderer_backend == RendererBackend::FilamentOpenGl ||
+             renderer_backend == RendererBackend::FilamentOpenGlHeadless) {
     window_flags |= SDL_WINDOW_OPENGL;
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
     SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0);
   } else {
-    mju_error("Unsupported window config: %d", render_config);
+    mju_error("Unsupported window config: %d", renderer_backend);
   }
 
   const float content_scale = ImGui_ImplSDL2_GetContentScaleForDisplay(0);
@@ -143,17 +149,18 @@ Window::Window(std::string_view title, int width, int height, Config config)
   }
 
   InitImGui(sdl_window_, content_scale, config.load_fonts,
-            (render_config != kClassicOpenGL));
+            (renderer_backend != RendererBackend::ClassicOpenGl));
 
-  if (render_config == kFilamentWebGL ||
-      (render_config == kClassicOpenGL && !config.offscreen_mode)) {
+  if (renderer_backend == RendererBackend::FilamentWebGl ||
+      (renderer_backend == RendererBackend::ClassicOpenGl &&
+       !config.offscreen_mode)) {
     SDL_GLContext gl_context = SDL_GL_CreateContext(sdl_window_);
     SDL_GL_MakeCurrent(sdl_window_, gl_context);
   }
 
-  if (config.offscreen_mode) {
+  if (config_.offscreen_mode) {
     sdl_renderer_ = SDL_CreateRenderer(sdl_window_, -1, SDL_RENDERER_SOFTWARE);
-    if (config.render_config == kClassicOpenGL) {
+    if (renderer_backend == RendererBackend::ClassicOpenGl) {
       InitOffscreenEglContext();
     }
   }
@@ -162,7 +169,7 @@ Window::Window(std::string_view title, int width, int height, Config config)
   SDL_VERSION(&wmi.version);
   SDL_GetWindowWMInfo(sdl_window_, &wmi);
 
-  if (!config.offscreen_mode) {
+  if (!config_.offscreen_mode) {
     #if defined(__linux__)
       native_window_ = reinterpret_cast<void*>(wmi.info.x11.window);
     #elif defined(__WIN32__)
@@ -270,7 +277,7 @@ void Window::Present(std::span<const std::byte> pixels) {
       }
     }
 
-    if (config_.render_config == kClassicOpenGL) {
+    if (config_.renderer_backend == RendererBackend::ClassicOpenGl) {
       dst = static_cast<unsigned char*>(surface->pixels);
       for (int r = 0; r < height_ / 2; ++r) {
         unsigned char* top_row = &dst[4 * width_ * r];
@@ -280,8 +287,8 @@ void Window::Present(std::span<const std::byte> pixels) {
     }
 
     SDL_RenderPresent(sdl_renderer_);
-  } else if (config_.render_config != kFilamentVulkan
-     && config_.render_config != kFilamentOpenGL) {
+  } else if (config_.renderer_backend != RendererBackend::FilamentVulkan
+     && config_.renderer_backend != RendererBackend::FilamentOpenGl) {
     SDL_GL_SwapWindow(sdl_window_);
   }
 }

src/experimental/platform/window.h

@@ -20,6 +20,8 @@
 #include <string>
 #include <string_view>
 
+#include "experimental/platform/renderer_backend.h"
+
 #if __has_include("third_party/GL/gl/include/EGL/egl.h")
 #define MUJOCO_STUDIO_EGL_SUPPORTED 1
 #include "third_party/GL/gl/include/EGL/egl.h"
@@ -35,16 +37,8 @@ namespace mujoco::platform {
 // handles events from the window.
 class Window {
  public:
-  // Configures the window for the specified rendering backend.
-  enum RenderConfig {
-    kClassicOpenGL,
-    kFilamentVulkan,
-    kFilamentOpenGL,
-    kFilamentWebGL,
-  };
-
   struct Config {
-    RenderConfig render_config = kClassicOpenGL;
+    RendererBackend renderer_backend = RendererBackend::ClassicOpenGl;
     bool enable_keyboard = true;
     bool load_fonts = true;
     bool offscreen_mode = false;

src/experimental/studio/app.cc

@@ -46,17 +46,6 @@
 
 namespace mujoco::studio {
 
-static constexpr platform::Window::RenderConfig kRenderConfig =
-#if defined(__EMSCRIPTEN__)
-  platform::Window::RenderConfig::kFilamentWebGL;
-#elif defined(USE_FILAMENT_VULKAN)
-  platform::Window::RenderConfig::kFilamentVulkan;
-#elif defined(USE_FILAMENT_OPENGL)
-  platform::Window::RenderConfig::kFilamentOpenGL;
-#elif defined(USE_CLASSIC_OPENGL)
-  platform::Window::RenderConfig::kClassicOpenGL;
-#endif
-
 static void ToggleFlag(mjtByte& flag) { flag = flag ? 0 : 1; }
 
 static void ToggleWindow(bool& window) {
@@ -115,7 +104,7 @@ static constexpr std::array<const char*, 31> kPercentRealTime = {
 App::App(Config config)
     : ini_path_(std::move(config.ini_path)) {
   platform::Window::Config window_config;
-  window_config.render_config = kRenderConfig;
+  window_config.renderer_backend = platform::Renderer::GetBackend();
   window_config.offscreen_mode = config.offscreen_mode;
   window_ = std::make_unique<platform::Window>("MuJoCo Studio", config.width,
                                                config.height, window_config);