feat(examples): add support for custom fonts directory via JSAR_SYSTEM_FONTS_DIR (#255)

Author: Copilot

src/common/font/cache.hpp

@@ -5,6 +5,7 @@
 #include <iostream>
 #include <unordered_map>
 #include <filesystem>
+#include <cstdlib>
 #include <assert.h>
 
 #include <skia/include/core/SkData.h>
@@ -288,6 +289,18 @@ namespace font
 #elif __ANDROID__
       addFontsAt("/system/fonts");
 #endif
+
+      // Check for custom system fonts directory from environment variable
+      const char *customFontsDir = std::getenv("JSAR_SYSTEM_FONTS_DIR");
+      if (customFontsDir != nullptr)
+      {
+        std::string fontPath(customFontsDir);
+        if (std::filesystem::exists(fontPath) && std::filesystem::is_directory(fontPath))
+        {
+          addFontsAt(fontPath);
+        }
+      }
+
       fontCollection_->setDefaultFontManager(fontMgr_);
       printSummary();
     }

src/examples/desktop_opengl.cpp

@@ -152,6 +152,7 @@ namespace jsar::example
       printf("                            singlepass - Single rendering pass\n");
       printf("  --env-map <path>        Specify environment map directory path\n");
       printf("  --no-env-map            Disable environment map rendering\n");
+      printf("  --system-fonts-dir <dir> Set custom system fonts directory\n");
       printf("  --help                  Show this help\n");
       printf("\n");
       printf("Examples:\n");
@@ -161,6 +162,7 @@ namespace jsar::example
       printf("  %s --stereo singlepass\n", programName);
       printf("  %s --env-map /path/to/cubemap  # Use custom environment map\n", programName);
       printf("  %s --no-env-map             # Disable environment map\n", programName);
+      printf("  %s --system-fonts-dir /usr/share/fonts  # Use custom font directory\n", programName);
     }
 
     bool init(int argc, char **argv)
@@ -279,6 +281,21 @@ namespace jsar::example
           if (samples < 0 || samples > 16)
             samples = 4;
         }
+        else if (arg == "--system-fonts-dir")
+        {
+          if (i + 1 >= argc)
+          {
+            printf("Error: --system-fonts-dir requires a directory path argument\n");
+            help(argv[0]);
+            return false;
+          }
+          string fontsDir = argv[++i];
+          if (setenv("JSAR_SYSTEM_FONTS_DIR", fontsDir.c_str(), 1) != 0)
+          {
+            printf("Error: Failed to set JSAR_SYSTEM_FONTS_DIR environment variable\n");
+            return false;
+          }
+        }
         else if (arg[0] != '-')
         {
           // This is the URL argument