Wasmfs: Support SDL2_image (#19560)

To do that we need to implement

emscripten_get_preloaded_image_data_from_FILE

This is implemented in JS in the old FS, which then does FS.getStream() etc.,
which is more than we want to support in the WasmFS JS API. Instead, just
implement that function in a simple way in wasm, which is much more
straightforward anyhow.

(That implementation is trivial aside from a new getPath() helper, but that
helper is useful anyhow - I've been using that code to debug locally.)

This also removes an SDL_Quit - removing that allows the test to actually
show the image that was loaded (otherwise we quit before the render
happens, which confused me as I was debugging).

Author: kripken

src/library_browser.js

@@ -1300,6 +1300,7 @@ var LibraryBrowser = {
     return 0;
   },
 
+#if !WASMFS // WasmFS implements this in wasm
   emscripten_get_preloaded_image_data_from_FILE__deps: ['emscripten_get_preloaded_image_data', 'fileno'],
   emscripten_get_preloaded_image_data_from_FILE__proxy: 'sync',
   emscripten_get_preloaded_image_data_from_FILE: function(file, w, h) {
@@ -1311,6 +1312,7 @@ var LibraryBrowser = {
 
     return 0;
   }
+#endif
 };
 
 autoAddDeps(LibraryBrowser, '$Browser');

system/lib/wasmfs/emscripten.cpp

@@ -0,0 +1,67 @@
+// Copyright 2023 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+//
+// This file contains implementations of emscripten APIs that are compatible
+// with WasmFS. These replace APIs in src/library*js, and basically do things
+// in a simpler manner for the situation where the FS is in wasm and not JS
+// (in particular, these implemenations avoid calling from JS to wasm, and
+// dependency issues that arise from that).
+//
+
+#include <emscripten.h>
+#include <stdio.h>
+
+#include <string>
+
+#include "file.h"
+#include "file_table.h"
+#include "wasmfs.h"
+
+namespace wasmfs {
+
+// Given an fd, returns the string path that the fd refers to.
+// TODO: full error handling
+// TODO: maybe make this a public API, as it is useful for debugging
+std::string getPath(int fd) {
+  auto fileTable = wasmfs::wasmFS.getFileTable().locked();
+
+  auto openFile = fileTable.getEntry(fd);
+  if (!openFile) {
+    return "!";
+  }
+
+  auto curr = openFile->locked().getFile();
+  std::string result = "";
+  while (curr != wasmfs::wasmFS.getRootDirectory()) {
+    auto parent = curr->locked().getParent();
+    // Check if the parent exists. The parent may not exist if curr was
+    // unlinked.
+    if (!parent) {
+      return "?/" + result;
+    }
+
+    auto parentDir = parent->dynCast<wasmfs::Directory>();
+    auto name = parentDir->locked().getName(curr);
+    result = '/' + name + result;
+    curr = parentDir;
+  }
+  return result;
+}
+
+} // namespace wasmfs
+
+extern "C"
+char *emscripten_get_preloaded_image_data_from_FILE(FILE *file,
+                                                    int *w,
+                                                    int *h) {
+  auto fd = fileno(file);
+  if (fd < 0) {
+    return 0;
+  }
+
+  auto path = wasmfs::getPath(fd);
+  return emscripten_get_preloaded_image_data(path.c_str(), w, h);
+}

test/browser/test_sdl2_image.c

@@ -74,8 +74,5 @@ int main() {
 
   printf("you should see an image.\n");
 
-  SDL_Quit();
-
   return result;
 }
-

test/test_browser.py

@@ -2945,6 +2945,7 @@ def test_sdl2_image_jpeg(self):
       '-sUSE_SDL=2', '-sUSE_SDL_IMAGE=2', '--use-preload-plugins'
     ])
 
+  @also_with_wasmfs
   @requires_graphics_hardware
   def test_sdl2_image_formats(self):
     shutil.copyfile(test_file('screenshot.png'), 'screenshot.png')

tools/system_libs.py

@@ -1857,6 +1857,7 @@ def get_files(self):
         filenames=['file.cpp',
                    'file_table.cpp',
                    'js_api.cpp',
+                   'emscripten.cpp',
                    'paths.cpp',
                    'special_files.cpp',
                    'support.cpp',