feat: add capture() function and expose viewportDimensions on ThermionViewer (allows easier saving of captured images to PNG)

thermion_dart/native/src/FilamentViewer.cpp

@@ -1186,6 +1186,49 @@ namespace thermion_filament
     #endif
   }
 
+  void FilamentViewer::capture(uint8_t *out, void (*onComplete)()) {
+      
+      Viewport const &vp = _view->getViewport();
+      size_t pixelBufferSize = vp.width * vp.height * 4;
+      auto *pixelBuffer = new uint8_t[pixelBufferSize];
+      auto callback = [](void *buf, size_t size, void *data)
+      {
+
+        auto frameCallbackData = (std::vector<void*>*)data;
+        uint8_t *out = (uint8_t *)(frameCallbackData->at(0));
+        void* callbackPtr = frameCallbackData->at(1);
+
+        void (*callback)(void) = (void (*)(void))callbackPtr;
+        memcpy(out, buf, size);
+        delete frameCallbackData;
+        callback();
+      };
+
+      auto userData = new std::vector<void*> { out, (void*)onComplete } ;
+
+      auto pbd = Texture::PixelBufferDescriptor(
+          pixelBuffer, pixelBufferSize,
+          Texture::Format::RGBA,
+          Texture::Type::UBYTE, nullptr, callback, userData);
+      _renderer->beginFrame(_swapChain, 0);
+      
+      _renderer->render(_view);
+
+      if(_rt) {
+        _renderer->readPixels(_rt, 0, 0, vp.width, vp.height, std::move(pbd));
+      } else { 
+        _renderer->readPixels(0, 0, vp.width, vp.height, std::move(pbd));
+      }
+      _renderer->endFrame();
+
+      #ifdef __EMSCRIPTEN__
+        _engine->execute();
+        emscripten_webgl_commit_frame();
+      #endif
+    }
+
+
+
   void FilamentViewer::savePng(void *buf, size_t size, int frameNumber)
   {
     // std::lock_guard lock(_recordingMutex);

thermion_dart/native/src/ThermionDartApi.cpp

@@ -329,6 +329,13 @@ extern "C"
         ((FilamentViewer *)viewer)->render(frameTimeInNanos, pixelBuffer, callback, data);
     }
 
+    EMSCRIPTEN_KEEPALIVE void capture(
+		const void *const viewer,
+		uint8_t *pixelBuffer,
+		void (*callback)(void)) {
+            ((FilamentViewer *)viewer)->capture(pixelBuffer, callback);
+        };
+
     EMSCRIPTEN_KEEPALIVE void set_frame_interval(
         const void *const viewer,
         float frameInterval)

thermion_dart/native/src/ThermionDartFFIApi.cpp

@@ -373,6 +373,12 @@ extern "C"
     auto fut = _rl->add_task(lambda);
   }
 
+  EMSCRIPTEN_KEEPALIVE void capture_ffi(void *const viewer, uint8_t* pixelBuffer, void (*onComplete)()) {
+    std::packaged_task<void()> lambda([=]() mutable
+                                      { capture(viewer, pixelBuffer, onComplete); });
+    auto fut = _rl->add_task(lambda);
+  }
+
   EMSCRIPTEN_KEEPALIVE void
   set_background_color_ffi(void *const viewer, const float r, const float g,
                            const float b, const float a)