Add support for progress feedback (#63)

CHANGELOG.md

@@ -8,6 +8,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 Uses libvips v8.15.1, compiled with Emscripten v3.1.52.
 
+### Added
+
+- Add `image.onProgress` callback for progress feedback.
+  [#63](https://github.com/kleisauke/wasm-vips/issues/63)
+
 ## [v0.0.7] - 2023-11-12
 
 Uses libvips v8.15.0, compiled with Emscripten v3.1.48.

build/preamble_vips.d.ts

@@ -506,6 +506,21 @@ declare module Vips {
          */
         readonly filename: string;
 
+        /**
+         * Attach progress feedback.
+         *
+         * This method can update user-interfaces with progress feedback,
+         * for example:
+         * ```js
+         * const image = vips.Image.newFromFile('huge.jpg');
+         * image.onProgress = (percent) =>
+         *   console.log(`${percent}% complete`);
+         * image.writeToFile('x.png');
+         * ```
+         * @param percent Percent complete.
+         */
+        onProgress: (percent: number) => void;
+
         //#region Constructor functions
 
         /**

src/bindings/image.cpp

@@ -93,6 +93,26 @@ void Image::call(const char *operation_name, Option *args,
     Image::call(operation_name, nullptr, args, kwargs, this);
 }
 
+void Image::eval_handler(VipsImage *image, VipsProgress *progress, void *user) {
+    Image *self = reinterpret_cast<Image *>(user);
+    if (self->progress_callback == nullptr)
+        return;
+
+    // Ensure that we call the JS function on the main thread, see:
+    // https://github.com/emscripten-core/emscripten/issues/11317
+    emscripten_sync_run_in_main_runtime_thread(
+        EM_FUNC_SIG_VI, self->progress_callback, progress->percent);
+}
+
+void Image::set_progress_callback(emscripten::val js_func) {
+    emscripten::val ptr = emscripten::val::module_property("addFunction")(
+        js_func, emscripten::val("vi"));
+    progress_callback = reinterpret_cast<void (*)(int)>(ptr.as<int>());
+
+    vips_image_set_progress(get_image(), 1);
+    g_signal_connect(get_image(), "eval", G_CALLBACK(eval_handler), this);
+}
+
 Image Image::new_memory() {
     return Image(vips_image_new_memory());
 }

src/bindings/image.h

@@ -11,6 +11,7 @@
 #include <vector>
 
 #include <emscripten/val.h>
+#include <emscripten/threading.h>
 
 namespace vips {
 
@@ -81,6 +82,15 @@ class Image : public Object {
         return vips_image_get_filename(get_image());
     }
 
+    static void eval_handler(VipsImage *image, VipsProgress *progress,
+                             void *user);
+
+    void set_progress_callback(emscripten::val js_func);
+
+    emscripten::val stub_getter() const {
+        return emscripten::val::null();
+    }
+
     const void *data() const {
         return vips_image_get_data(get_image());
     }
@@ -612,6 +622,10 @@ class Image : public Object {
 
         return out;
     }
+
+ private:
+    // sig = vi
+    void (*progress_callback)(int percent) = nullptr;
 };
 
 }  // namespace vips

src/vips-emscripten.cpp

@@ -1104,6 +1104,9 @@ EMSCRIPTEN_BINDINGS(my_module) {
         .property("xres", &Image::xres)
         .property("yres", &Image::yres)
         .property("filename", &Image::filename)
+        // Handwritten setters
+        .property("onProgress", &Image::stub_getter,
+                  &Image::set_progress_callback)
         // Auto-generated (class-)functions
         .class_function("analyzeload", &Image::analyzeload)
         .class_function("analyzeload", optional_override([](const std::string &filename) {