Use mjResourceProvider instead of custom LoadAsset callbacks.

PiperOrigin-RevId: 853172824
Change-Id: I60ef1207611c4da119cc3f0a7819088cffca6e4f

src/experimental/studio/main.cc

@@ -15,43 +15,88 @@
 // Main entry point for the Filament-based MuJoCo renderer.
 
 #include <cstddef>
-#include <cstdint>
 #include <cstdlib>
 #include <fstream>
+#include <ios>
+#include <iosfwd>
+#include <optional>
 #include <string>
 #include <string_view>
 #include <vector>
 
 #include <absl/flags/flag.h>
+#include <mujoco/mujoco.h>
 #include "experimental/studio/app.h"
 
 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.");
 
-static std::vector<std::byte> LoadAsset(std::string_view path) {
-  std::string fullpath = std::string("assets/") + std::string(path);
-  std::ifstream file(fullpath, std::ios::binary | std::ios::ate);
-  if (!file.is_open()) {
-    return {};
-  }
-  std::streampos file_size = file.tellg();
-  file.seekg(0, std::ios::beg);
-  std::vector<std::byte> buffer(file_size);
-  if (!file.read(reinterpret_cast<char*>(buffer.data()), file_size)) {
-    return {};
-  }
-  return buffer;
+std::string Resolve(std::string_view path) {
+  return std::string("assets/") + std::string(path);
 }
 
+class FileResource {
+ public:
+  explicit FileResource(const std::string& path)
+      : file_(path, std::ios::binary | std::ios::ate) {
+    if (!file_.is_open()) {
+      mju_warning("Cannot open file %s", path.c_str());
+      return;
+    }
+
+    size_ = file_.tellg();
+    file_.seekg(0, std::ios::beg);
+  }
+
+  int Read(const void** buffer) {
+    buffer_.resize(size_);
+    if (!file_.read(reinterpret_cast<char*>(buffer_.data()), size_)) {
+      return 0;
+    }
+    *buffer = buffer_.data();
+    return size_;
+  }
+
+  int Size() const { return size_; }
+
+  FileResource(const FileResource&) = delete;
+  FileResource& operator=(const FileResource&) = delete;
+
+ private:
+  std::ifstream file_;
+  std::vector<char> buffer_;
+  int size_ = 0;
+};
+
 int main(int argc, char** argv, char** envp) {
 
   const char* home = getenv("HOME");
   const std::string ini_path = std::string(home ? home : ".") + "/.mujoco.ini";
 
+  mjpResourceProvider resource_provider;
+  resource_provider.open = [](mjResource* resource) {
+    const std::string resolved_path = Resolve(resource->name);
+    FileResource* f = new FileResource(resolved_path);
+    resource->data = f;
+    return f->Size();
+  };
+  resource_provider.read = [](mjResource* resource, const void** buffer) {
+    FileResource* f = static_cast<FileResource*>(resource->data);
+    return f->Read(buffer);
+  };
+  resource_provider.close = [](mjResource* resource) {
+    delete static_cast<FileResource*>(resource->data);
+  };
+
+  resource_provider.prefix = "font";
+  mjp_registerResourceProvider(&resource_provider);
+  resource_provider.prefix = "filament";
+  mjp_registerResourceProvider(&resource_provider);
+
   const int width = absl::GetFlag(FLAGS_window_width);
   const int height = absl::GetFlag(FLAGS_window_height);
-  mujoco::studio::App app(width, height, ini_path, LoadAsset);
+  mujoco::studio::App app(width, height, ini_path);
 
   // If the model file is not specified, try to load it from the first argument
   std::string model_file = absl::GetFlag(FLAGS_model_file);