This patch switches to instance methods of draw and display for
ASTextNode and ASImageNode to attempt to increase their performance.
It also fixes some thread safety issues in ASImageNode which appear
to have been regressions (though probably not hit very often).
And it sets up work for allowing modification of CGContexts before
and after a node's contents are drawn.
Before, it was expensive to check this value, even though it was rarely set.
Now the cost is moved to setting the value, and is made very cheap to check with _hierarchyState.
Later, this will be added to ASViewController. Right now it is not hooked up to drive anything.
It will become the codepath that drives calls like -fetchData and -clearContents.
This ensures memory cleanup happens correctly and introduces a new test project
to support developing new features while stressing tough use cases for correctness.
This provides internal features on _ASAsyncTransaction and ASDisplayNode to facilitate
implementing public API that allows clients to choose if they would prefer to block
on the completion of unfinished rendering, rather than allow a placeholder state to
become visible.
The internal features are:
-[_ASAsyncTransaction waitUntilComplete]
-[ASDisplayNode recursivelyEnsureDisplay]
Also provided are two such implementations:
-[ASCellNode setNeverShowPlaceholders:], which integrates with both Tables and Collections
-[ASViewController setNeverShowPlaceholders:], which should work with Nav and Tab controllers.
Lastly, on ASDisplayNode, a new property .shouldBypassEnsureDisplay allows individual node types
to exempt themselves from blocking the main thread on their display.
By implementing the feature at the ASCellNode level rather than ASTableView & ASCollectionView,
developers can retain fine-grained control on display characteristics. For example, certain
cell types may be appropriate to display to the user with placeholders, whereas others may not.
Follow-up work will include unit tests, revisiting names, and the header locations of definitions.
- -layoutSpecThatFits: must return an ASLayoutSpec.
- Move ASDisplayNode's -measureWithSizeRange: redeclaration to ASDisplayNode.h.
- Rename ASStackLayoutChild.h to ASStackLayoutDefines.h.
- Rename ASStaticLayoutSpecDimension.h to ASRelativeSize.h.
- Don't import ASLayout.h in other headers to prevent circular inclusions.
- Explain use cases of ASLayout's initializers.
- Clean up ASInternalHelpers.h.
- constrainedSizeForCalculatedLayout is of type ASSizeRange.
- calculatedLayout is better explained.
- Since ASLayout is cached and reused, its position property is mutable.
