Remove Window::open_as_if_parented #153
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Engid
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Dec 12, 2023
The open_as_if_parented method was intended to support the use case of Audio Unit plugin views. However, the Audio Unit API differs in important ways from other plugin APIs (such as VST 3 and CLAP) with regard to the lifetime management of the plugin's NSView, and trying to support both lifetime management patterns simultaneously has been the source of complexity and bugs. Thus, rather than implementing Audio Unit NSView management directly in Baseview, it will be the responsibility of plugin frameworks to implement a compatibility layer between the Audio Unit API and the Baseview API.
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Instead of trying to detect when to clean up the window based on the `NSView`'s retain count, require window cleanup to be initiated explicitly via `Window::close`, `WindowHandle::close`, or `[NSWindowDelegate windowShouldClose:]` (in non-parented mode; called when the user clicks the "X" button). This fixes the leaks and use-after-frees that can be caused by the inherent unreliability of the retain count logic. As discussed in #153, this change essentially means that the `NSView` created by Baseview will not be suitable as the top-level view for an Audio Unit, since the Baseview API now requires that child windows be cleaned up by an explicit call to `WindowHandle::close`, and the only reliable signal for cleaning up an Audio Unit view is a call to `[NSView dealloc]`. However, this does not mean that Baseview cannot be used in the context of an Audio Unit; it just means that plugin frameworks must implement a compatibility layer with a wrapper `NSView` (which is the approach taken by JUCE). In order to implement this change: - `WindowState` is stored in an `Rc` rather than a `Box`. - `WindowHandle` holds an `Rc<WindowState>` so that `WindowHandle::close` can directly invoke window cleanup logic. - Since the window can be closed during an event handler, `WindowState::from_view` now returns a clone of the `Rc<WindowState>` held by the `NSView` to ensure that it lives until the end of an event handler. - In the non-parented case, the `NSView` is set as the window delegate, which allows it to receive the `windowShouldClose:` call when the user clicks the "X" button, upon which it will dispatch the `WillClose` event and initiate window cleanup logic. - `Window::open_parented` and `open_blocking` no longer `release` the `NSView` immediately after attaching it. Instead, the `NSView` is released as part of the cleanup logic in `WindowInner::close`. - `Window::resize` now checks if the window is open to avoid using the `NSView` after releasing it. - The overridden `release` method, the `retain_count_after_build` field, the `ParentHandle` struct, and the `close_requested` flag have all been removed.
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The open_as_if_parented method was intended to support the use case of Audio Unit plugin views. However, the Audio Unit API differs in important ways from other plugin APIs (such as VST 3 and CLAP) with regard to the lifetime management of the plugin's NSView, and trying to support both lifetime management patterns simultaneously has been the source of complexity and bugs. Thus, rather than implementing Audio Unit NSView management directly in Baseview, it will be the responsibility of plugin frameworks to implement a compatibility layer between the Audio Unit API and the Baseview API.