Changelog (2.0.0-beta.2)

Changes since 2.0.0-beta.1.

Last updated: October 2nd, 2026

📘 See the full changelog for 2.0.0

These are the changes since 2.0.0-beta.1 (released August 28th, 2026). For all changes since v1.4, see the 2.0.0 changelog.

#Highlights

• Linux x64 support. The beta SDK now ships for Linux x64, alongside Windows x64 and macOS arm64. It needs glibc 2.31 or newer and an X11 desktop (Wayland desktops work through XWayland, native Wayland support coming soon). Apps need GCC 11 or later, or a C++20 clang.
• Less work per frame. Each frame repaints only what changed (better damage-tracking support in the compositor). On the CPU renderer, scrolling now moves existing pixels instead of repainting the page (much better scroll performance).
• Smoother animation. Each frame, the animation clock (CSS animations, rAF, scroll, etc.) is now timed to the physical display's future refresh timestamp for smoother animations and better latency.
• Final bridge APIs. The JavaScript bridge, DOM API, and data bindings API have changed (more consistent API naming, ownership rules, and error handling). Most apps that use them need changes; see "Upgrading from beta.1".
• Developer mode. Config::diagnostics turns on bridge warnings and sets the minimum log level in one place.
• No white flash at startup. Window::ShowWhenReady() shows a window once its pages are ready.
• Pixel-art scaling. CSS image-rendering: pixelated and canvas imageSmoothingEnabled now work on both renderers.

#Upgrading from beta.1

Recompile everything against the beta.2 headers. Then check the two lists below.

#Changes the compiler won't catch

Some of the API behavior has changed, make sure to be aware of the following changes:

Object lifetimes:

• A View no longer keeps your JS/DOM/data-binding bridge objects alive. When you destroy the last js::API, dom::Triggers, or dom::data::Context, the bridge object detaches from every View. Keep these objects alive for as long as pages should use them.
• Destroying a dom::EventListener no longer removes the listener. Call Remove() on it, or add it with a dom::AbortController signal.
• C API: these functions now return handles you must destroy:
  • ulDOMEventGetTarget() and the other event target getters;
  • ulDOMDataBindingGetContext();
  • ulJSAPIGetDiagnosticsAPI().
• C API: when a call that takes a destroy_user_data callback fails, the library now calls destroy_user_data for you. Don't free user_data yourself after a failed call.

Logging and diagnostics:

• Bridge diagnostics are off unless you set Config::diagnostics.developer_mode = true.
• LogLevel (and the C ULLogLevel) now starts with Fatal and ends with Debug, so the numeric values of Error, Warning, and Info went up by one. Update any code that stores or compares these numbers.
• Every log message now starts with a category tag such as [render] or [net]. Debug messages are not sent to your Logger unless you lower Config::diagnostics.min_log_level.
• AppCore's error dialog now appears only for Fatal messages, not for every Error.

Custom surfaces:

• The CPU renderer now repaints only the area that changed. A custom Surface must keep its pixels from one frame to the next.
• Surface::set_dirty_bounds() now adds to the dirty area instead of replacing it.
• The library now destroys Surfaces through SurfaceFactory::DestroySurface(). Before, it deleted them directly.

JavaScript:

• Value::To<int>() (and other integer conversions) now return an error for a non-integer or out-of-range number instead of truncating it.
• JSValueGetType() and ulJSValueGetType() return a new BigInt type for a BigInt, where they used to return the object type.

AppCore:

• Hidden windows are no longer painted, so pages in a hidden window don't finish loading until the window is shown. Use Window::ShowWhenReady() to show a window once its pages are ready.
• requestAnimationFrame() timestamps now point to future timestamps (when the frame will reach the physical screen), slightly ahead of performance.now(). Set Settings::sync_animations_to_present = false to keep the old timing.

Data bindings:

• Context::PostTask() with a callable that takes no dom::Document now runs once, not once per View.
• ul-attr: no longer sets class, style, or on* attributes. Use ul-class-* and ul-style-*.
• ul-on:submit now always prevents the form from submitting.
• {{path}} is no longer filled in inside <script>, <style>, or <textarea>. Use ul-value for a textarea.
• C API: a string length of 0 now means an empty string. Before, the library called strlen().

#Changes the compiler will catch

When you rebuild the compiler should flag each of these changes. In the tables below, the left column is beta.1 code and the right column is the equivalent in beta.2.

View:

• Injection filter callbacks now receive one request struct instead of five arguments. The struct has the same values as before: view, the API or triggers handle, origin, is_main_frame, and rules_allow.

JavaScript (ultralight::js):

• On the left, ctx is a raw ULJSContext. On the right, context is a js::Context: create one from a View (js::Context context(view)), or use info.context() inside a binding.
• An operation on an empty handle now fails with error.is_empty(), not is_page_gone().
• Value::type() returns the new js::Type enum instead of ULJSType.
• On C++23, js::Result is no longer std::expected. Use js::Unexpected instead of std::unexpected.

DOM (ultralight::dom):

These members changed type:

• Calls that can fail, such as querySelector(), appendChild(), and matches(), now return their value directly, as they do in JavaScript. To get the dom::Result<T> back, pass dom::Checked as the last argument: el.querySelector(sel, dom::Checked).
• dom::Event can't be copied. Take const dom::Event& in your own functions.

Data bindings (ultralight::dom::data):

• Field names in Schema() must be identifiers: "max_hp" works and "max-hp" doesn't.
• OnChange and OnAction handlers must take the field's exact type. For example, a float parameter for an int field no longer compiles.
• A field with a validator must be dd::Editable.

C API:

• ulViewAttachDOMDataContext() now takes (view, context, flags, origin_rules, num_origin_rules) and returns bool.
• ULCursor, ULMessageSource, and ULMessageLevel moved to CAPI_View.h. Code that includes <Ultralight/CAPI.h> is unaffected.

Platform interfaces:

• Surface has a new required method, Scroll(). Most implementations can call Surface::ShiftPixels() on their pixel buffer. In the C API, the scroll callback is optional.
• FontFile has a new required method, face_index(). This only matters if you subclass FontFile directly.
• Renderer::RenderOnly() is deprecated. Use Render(), and hide a View with View::set_visible(false).
• If you copied code from the SDK's platform/ folder (GPU drivers, clipboards, audio outputs), replace it with the beta.2 copies. The beta.2 copies need the beta.2 library, and the shaders changed.

#What's New

Rendering:

• Repaint only what changed each frame, and skip frames with no changes, on both renderers
• Scroll on the CPU renderer by moving pixels instead of repainting
• Redraw only the changed area on the GPU when a custom driver sets GPUDeviceCaps::supports_partial_redraw (all reference drivers set it)
• Add CSS image-rendering: pixelated / crisp-edges and canvas imageSmoothingEnabled / imageSmoothingQuality
• Time animations, requestAnimationFrame(), and smooth scrolling to the display's refresh
• Add Renderer::RefreshDisplay(display_id, target_timestamp), SetDisplayRefreshRate(), and SetDisplayUsesCustomClock() for apps that drive their own frame timing
• Load the requested face of a .ttc font collection instead of the first face

APIs:

• Add Config::diagnostics: developer mode, JavaScript and DOM warning levels, and the minimum log level
• Add Surface::dirty_rect() / dirty_rect_count() so a custom surface can copy only the regions that changed
• Add ViewConfig::allow_universal_access_from_file_urls (on by default, as in beta.1)
• DOM: dom::AbortController, listener options (once, passive, signal), dom::NodeList, text and comment nodes, append() / before() / remove(), form validation, element offsets and scrolling, and camelCase style names (el.style.fontSize)
• JavaScript: js::Or() for reading a value with a fallback, error locations (stack(), line(), column()), and API::DumpSchema()
• Data bindings: Binding::IsAlive(), Context::DumpSchema(), and the ul-on:<event>.prevent modifier

AppCore:

• Add Window::ShowWhenReady()
• Add App::monitor_count() and App::monitor()
• On Linux: OpenGL rendering, CPU-only windows with no GPU (Settings::force_cpu_renderer), PulseAudio media output, clipboard, and IME

SDK:

• Ship the data-binding mockup tools (gen-mock-data.py, ul-mock.js) and gen-typescript.py in tools/scripts/. gen-typescript.py replaces generate_dts.py
• Update the API documentation in most public headers

#Notable Fixes

• Fix position: fixed and sticky elements shaking at fractional display scales
• Fix overlay scrollbars showing through elements stacked above them
• Fix window.close(), View::CancelDownload(), and OnUpdateHistory(), which did nothing in beta.1
• Fix right-click not firing contextmenu, Ctrl- and Shift-click modifiers, and wheelDelta values
• Fix in-memory Sessions saving localStorage to disk
• Fix a second ULView handle for the same View turning off the first handle's callbacks
• Fix ulCreateRenderer() returning a handle when it failed (it now returns NULL)
• Fix ultralight_copy_runtime_files() putting resources in the wrong folder of a macOS app bundle
• Fix the public headers failing to compile with GCC or after X11 headers

#Known Issues

• On Windows, App::monitor_count() always returns 1 (monitor enumeration works on macOS and Linux)