From b0dd56659d79417cc522874dd3c5dcc2db28bb75 Mon Sep 17 00:00:00 2001
From: HoofedEar <1261392+HoofedEar@users.noreply.github.com>
Date: Wed, 3 Dec 2025 17:57:26 -0800
Subject: [PATCH] a working baseline for Emscripten builds

---
 3rdParty/Lua/CMakeLists.txt |  4 ++++
 CMake/emscripten_pre.js     | 45 +++++++++++++++++++++++++++++++++++++
 CMakeLists.txt              | 18 +++++++++++----
 Source/diablo.cpp           |  4 ++++
 Source/engine/dx.cpp        |  9 ++++++++
 5 files changed, 76 insertions(+), 4 deletions(-)
 create mode 100644 CMake/emscripten_pre.js

diff --git a/3rdParty/Lua/CMakeLists.txt b/3rdParty/Lua/CMakeLists.txt
index 04147a54d..a031ffca4 100644
--- a/3rdParty/Lua/CMakeLists.txt
+++ b/3rdParty/Lua/CMakeLists.txt
@@ -26,6 +26,10 @@ if(CMAKE_SYSTEM_NAME MATCHES "Darwin" AND DARWIN_MAJOR_VERSION VERSION_EQUAL 8)
   # localtime_r gmtime_r
   find_package(MacportsLegacySupport REQUIRED)
   target_link_libraries(lua_static PRIVATE MacportsLegacySupport::MacportsLegacySupport)
+elseif(EMSCRIPTEN)
+  # Enable pthread support for Emscripten to match SDL2's USE_PTHREADS=1
+  target_compile_options(lua_static PUBLIC -pthread)
+  target_link_options(lua_static PUBLIC -pthread)
 elseif(TARGET_PLATFORM STREQUAL "dos")
   target_compile_definitions(lua_static PUBLIC -DLUA_USE_C89)
 elseif(ANDROID AND ("${ANDROID_ABI}" STREQUAL "armeabi-v7a" OR "${ANDROID_ABI}" STREQUAL "x86"))
diff --git a/CMake/emscripten_pre.js b/CMake/emscripten_pre.js
new file mode 100644
index 000000000..ba9cf6177
--- /dev/null
+++ b/CMake/emscripten_pre.js
@@ -0,0 +1,45 @@
+// Pre-load MPQ files from the server directory into Emscripten virtual filesystem
+Module['preRun'] = Module['preRun'] || [];
+Module['preRun'].push(function() {
+  // List of MPQ files to try loading (in priority order)
+  var mpqFiles = [
+    'diabdat.mpq',
+    'DIABDAT.MPQ',
+    'spawn.mpq',
+    'hellfire.mpq',
+    'hfmonk.mpq',
+    'hfmusic.mpq',
+    'hfvoice.mpq',
+    'hfbard.mpq',
+    'hfbarb.mpq'
+  ];
+
+  // Create a promise-based loading system
+  var loadPromises = mpqFiles.map(function(filename) {
+    return new Promise(function(resolve) {
+      fetch(filename)
+        .then(function(response) {
+          if (response.ok) {
+            return response.arrayBuffer();
+          }
+          throw new Error('File not found');
+        })
+        .then(function(data) {
+          console.log('Loading ' + filename + ' into virtual filesystem...');
+          FS.writeFile('/' + filename, new Uint8Array(data));
+          console.log('Successfully loaded ' + filename);
+          resolve();
+        })
+        .catch(function() {
+          // File doesn't exist, skip silently
+          resolve();
+        });
+    });
+  });
+
+  // Wait for all MPQ files to load before continuing
+  Module.addRunDependency('loadMPQs');
+  Promise.all(loadPromises).then(function() {
+    Module.removeRunDependency('loadMPQs');
+  });
+});
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 08767a37e..9d6bc4652 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -271,7 +271,10 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang" AND NOT PS4)
   if(APPLE)
     add_link_options("$<$<NOT:$<CONFIG:Debug>>:LINKER:-dead_strip>")
   else()
-    add_link_options("$<$<NOT:$<CONFIG:Debug>>:LINKER:--gc-sections,--as-needed>")
+    add_link_options("$<$<NOT:$<CONFIG:Debug>>:LINKER:--gc-sections>")
+    if(NOT EMSCRIPTEN)
+      add_link_options("$<$<NOT:$<CONFIG:Debug>>:LINKER:--as-needed>")
+    endif()
   endif()
 endif()
 
@@ -301,7 +304,7 @@ endif()
 
 # Not a genexp because CMake doesn't support it
 # https://gitlab.kitware.com/cmake/cmake/-/issues/20546
-if(NOT DISABLE_LTO)
+if(NOT DISABLE_LTO AND NOT EMSCRIPTEN)
   # LTO if supported:
   include(CheckIPOSupported)
   check_ipo_supported(RESULT is_ipo_supported OUTPUT lto_error)
@@ -369,7 +372,7 @@ else()
     Packaging/windows/devilutionx.rc
     Packaging/apple/LaunchScreen.storyboard)
 
-    if(CMAKE_STRIP AND NOT DEVILUTIONX_DISABLE_STRIP)
+    if(CMAKE_STRIP AND NOT DEVILUTIONX_DISABLE_STRIP AND NOT EMSCRIPTEN)
       add_custom_command(
         TARGET ${BIN_TARGET} POST_BUILD
         COMMAND $<$<OR:$<CONFIG:Release>,$<CONFIG:MinSizeRel>>:${CMAKE_STRIP}>
@@ -398,7 +401,14 @@ include(Assets)
 include(Mods)
 
 if(EMSCRIPTEN)
-  target_link_options(${BIN_TARGET} PRIVATE --preload-file assets)
+  target_link_options(${BIN_TARGET} PRIVATE
+    --preload-file assets
+    -sFORCE_FILESYSTEM=1
+    -sALLOW_MEMORY_GROWTH=1
+    -sASYNCIFY
+  )
+  # Add JavaScript to load MPQ files from the server directory at runtime
+  target_link_options(${BIN_TARGET} PRIVATE --pre-js ${CMAKE_CURRENT_SOURCE_DIR}/CMake/emscripten_pre.js)
 endif()
 
 if(NOT USE_SDL1 AND NOT UWP_LIB)
diff --git a/Source/diablo.cpp b/Source/diablo.cpp
index 4f51b7a76..da35c39ed 100644
--- a/Source/diablo.cpp
+++ b/Source/diablo.cpp
@@ -168,7 +168,11 @@ bool gbGameLoopStartup;
 bool forceSpawn;
 bool forceDiablo;
 int sgnTimeoutCurs;
+#ifdef __EMSCRIPTEN__
+bool gbShowIntro = false; // Skip intro videos in browser for performance
+#else
 bool gbShowIntro = true;
+#endif
 /** To know if these things have been done when we get to the diablo_deinit() function */
 bool was_archives_init = false;
 /** To know if surfaces have been initialized or not */
diff --git a/Source/engine/dx.cpp b/Source/engine/dx.cpp
index 60c792ec8..d7a77acf5 100644
--- a/Source/engine/dx.cpp
+++ b/Source/engine/dx.cpp
@@ -17,6 +17,10 @@
 #include <SDL.h>
 #endif
 
+#ifdef __EMSCRIPTEN__
+#include <emscripten.h>
+#endif
+
 #include "controls/control_mode.hpp"
 #include "controls/plrctrls.h"
 #include "engine/render/primitive_render.hpp"
@@ -259,6 +263,11 @@ void RenderPresent()
 		}
 		SDL_RenderPresent(renderer);
 
+#ifdef __EMSCRIPTEN__
+		// Yield to browser to allow rendering
+		emscripten_sleep(1);
+#endif
+
 		if (*GetOptions().Graphics.frameRateControl != FrameRateControl::VerticalSync) {
 			LimitFrameRate();
 		}