Support examples with Emterpreter

Examples can be compiled for web with no code change at all! Usually
examples need to be refactored for web... using emscripten code
interpreter (emterpreter), it can manage synchronous while() loops
internally... as a downside, execution is very slow...

examples/Makefile

@@ -117,13 +117,13 @@ endif
 
 ifeq ($(PLATFORM),PLATFORM_WEB)
     # Emscripten required variables
-    EMSDK_PATH = C:/emsdk
-    EMSCRIPTEN_VERSION = 1.37.28
-    CLANG_VERSION=e1.37.28_64bit
-    PYTHON_VERSION=2.7.5.3_64bit
-    NODE_VERSION=4.1.1_64bit
-    export PATH=$(EMSDK_PATH);$(EMSDK_PATH)\clang\$(CLANG_VERSION);$(EMSDK_PATH)\node\$(NODE_VERSION)\bin;$(EMSDK_PATH)\python\$(PYTHON_VERSION);$(EMSDK_PATH)\emscripten\$(EMSCRIPTEN_VERSION);C:\raylib\MinGW\bin:$$(PATH)
-    EMSCRIPTEN=$(EMSDK_PATH)\emscripten\$(EMSCRIPTEN_VERSION)
+    EMSDK_PATH          = C:/emsdk
+    EMSCRIPTEN_VERSION  = 1.38.8
+    CLANG_VERSION       = e1.38.8_64bit
+    PYTHON_VERSION      = 2.7.13.1_64bit\python-2.7.13.amd64
+    NODE_VERSION        = 8.9.1_64bit
+    export PATH         = $(EMSDK_PATH);$(EMSDK_PATH)\clang\$(CLANG_VERSION);$(EMSDK_PATH)\node\$(NODE_VERSION)\bin;$(EMSDK_PATH)\python\$(PYTHON_VERSION);$(EMSDK_PATH)\emscripten\$(EMSCRIPTEN_VERSION);C:\raylib\MinGW\bin:$$(PATH)
+    EMSCRIPTEN          = $(EMSDK_PATH)\emscripten\$(EMSCRIPTEN_VERSION)
 endif
 
 # Define raylib release directory for compiled library.
@@ -236,14 +236,23 @@ ifeq ($(PLATFORM),PLATFORM_RPI)
     CFLAGS += -std=gnu99
 endif
 ifeq ($(PLATFORM),PLATFORM_WEB)
-    # -O2                        # if used, also set --memory-init-file 0
+    # -Os                        # size optimization
+    # -O2                        # optimization level 2, if used, also set --memory-init-file 0
     # --memory-init-file 0       # to avoid an external memory initialization code file (.mem)
     # -s ALLOW_MEMORY_GROWTH=1   # to allow memory resizing
     # -s TOTAL_MEMORY=16777216   # to specify heap memory size (default = 16MB)
     # -s USE_PTHREADS=1          # multithreading support
     # -s WASM=1                  # support Web Assembly (https://github.com/kripken/emscripten/wiki/WebAssembly)
+    # -s EMTERPRETIFY=1          # enable emscripten code interpreter (very slow)
+    # -s EMTERPRETIFY_ASYNC=1    # support synchronous loops by emterpreter
+    # --profiling                # include information for code profiling
     # --preload-file resources   # specify a resources folder for data compilation
-    CFLAGS += -s USE_GLFW=3 -s ASSERTIONS=1 -s WASM=1 --profiling --preload-file resources
+    CFLAGS += -Os -s USE_GLFW=3 -s ASSERTIONS=1 -s WASM=1 -s EMTERPRETIFY=1 -s EMTERPRETIFY_ASYNC=1
+    
+    # NOTE: Simple raylib examples are compiled to be interpreter by emterpreter, that way,
+    # we can compile same code for ALL platforms with no change required, but, working on bigger
+    # projects, code needs to be refactored to avoid a blocking while() loop, moving Update and Draw
+    # logic to a self contained function: UpdateDrawFrame(), check core_basic_window_web.c for reference.
 
     # Define a custom shell .html and output extension
     CFLAGS += --shell-file $(RAYLIB_PATH)\templates\web_shell\shell.html

src/core.c

@@ -141,6 +141,9 @@
 #endif
 
 #if defined(PLATFORM_DESKTOP) || defined(PLATFORM_WEB)
+    #if defined(PLATFORM_WEB)
+        #define GLFW_INCLUDE_ES2
+    #endif
     //#define GLFW_INCLUDE_NONE     // Disable the standard OpenGL header inclusion on GLFW3
     #include <GLFW/glfw3.h>         // GLFW3 library: Windows, OpenGL context and Input management
                                     // NOTE: GLFW3 already includes gl.h (OpenGL) headers
@@ -634,7 +637,17 @@ bool IsWindowReady(void)
 // Check if KEY_ESCAPE pressed or Close icon pressed
 bool WindowShouldClose(void)
 {
-#if defined(PLATFORM_DESKTOP) || defined(PLATFORM_WEB)
+#if defined(PLATFORM_WEB)
+    // Emterpreter-Async required to run sync code
+    // https://github.com/kripken/emscripten/wiki/Emterpreter#emterpreter-async-run-synchronous-code
+    // By default, this function is never called on a web-ready raylib example because we encapsulate
+    // frame code in a UpdateDrawFrame() function, to allow browser manage execution asynchronously
+    // but now emscripten allows sync code to be executed in an interpreted way, using emterpreter!
+    emscripten_sleep(16);
+    return false;
+#endif
+    
+#if defined(PLATFORM_DESKTOP)
     if (windowReady)
     {
         // While window minimized, stop loop execution