Add emscripten async bitmap

src/bitmap.cpp

@@ -44,6 +44,10 @@
 #include "font.h"
 #include "eventthread.h"
 
+#ifdef __EMSCRIPTEN__
+#include <emscripten.h>
+#endif
+
 #define GUARD_MEGA \
 	{ \
 		if (p->megaSurface) \
@@ -233,6 +237,39 @@ struct BitmapPrivate
 	}
 };
 
+#ifdef __EMSCRIPTEN__
+EM_JS(void, load_file_async, (const char* fullPathC), {
+	Asyncify.handleSleep(function(wakeUp) {
+		const fullPath = UTF8ToString(fullPathC);
+
+		// Make cache object
+		if (!window.fileAsyncCache) window.fileAsyncCache = {};
+
+		// Check if already loaded
+		if (window.fileAsyncCache.hasOwnProperty(fullPath)) return wakeUp();
+
+		// Get full destination
+		const file = "game/" + fullPath;
+
+		// Get path and filename
+		const path = "/" + file.substring(0, file.lastIndexOf("/"));
+		const filename = file.substring(file.lastIndexOf("/") + 1);
+
+		// Get target URL
+		const iurl = "gameasync/" + fullPath;
+
+		// Delete original file
+		FS.unlink(path + "/" + filename);
+
+		// Get the new file
+		FS.createPreloadedFile(path, filename, iurl, true, true, function() {
+			window.fileAsyncCache[fullPath] = 1;
+			wakeUp();
+		}, console.error);
+	});
+});
+#endif;
+
 struct BitmapOpenHandler : FileSystem::OpenHandler
 {
 	SDL_Surface *surf;
@@ -244,6 +281,7 @@ struct BitmapOpenHandler : FileSystem::OpenHandler
 	bool tryRead(SDL_RWops &ops, const char *ext, const char * fullPath)
 	{
 #ifdef __EMSCRIPTEN__
+		load_file_async(fullPath);
 		surf = IMG_Load(fullPath);
 #else
 		surf = IMG_LoadTyped_RW(&ops, 1, ext);