Added a ScrollListener listener to Scrollable. The ScrollListener runs each time the Scrollable's scrollOffset changes. This can be used to keep overlay widgets in sync with a Scrollable below them.
Removed the Scrollable ScrollClient API. It was no longer used and was clumsy to use as a ScrollListener.
Added global function findScrollableAncestor() to scrollable.dart.
Added examples/widgets/overlay_geometry.dart. The app's Scaffold is contained by a Stack. The Stack is used to display green overlay "Markers" at the corners of the most recently selected list item and where the corresponding tap occurred. The app uses widget.localToGlobal() to compute the global overlay positions of the markers. The ScrollListener is used to keep the markers' positions up to date.
Using ImageResource solves two problems:
1) Listeners can be notified synchronously when the sky.Image is already
available. This change removes flash of 0x0 layout when moving an
already-cached image around in the render tree.
2) In the future, when we support animated images, we can notify listeners
multiple times whenever a new image is available.
This patch simplifies the SkPicture we generate for Skia. Instead of drawing
everything into a nested SkPicture, we now draw everything into the top-level
picture, which requires us to apply the device scale factor in Dart.
New asserts:
- verify that after layout, the size fits the constraints
- verify that after layout, the size isn't infinite
- verify that you don't set the size in performLayout() if you have
sizedByParent set
- verify that nobody reads your size during layout except you, or your
parent if they said parentUsesSize:true
Fixes some bugs found by those asserts:
- RenderBlock, RenderStack, and RenderScaffold were not always setting
parentUsesSize correctly
- RenderScaffold was setting its slot entries to null rather than
removing them when the slot went away, which led to null derefs in
certain circumstances
Also, rename a local variable in RenderStack.performLayout() because
it was shadowing a variable on the object itself, which was really
confusing when I first tried to debug this function...
R=abarth@chromium.org
Review URL: https://codereview.chromium.org/1213473003.
This also fixes the C++ side to give the right baseline information.
Previously it was giving the baseline distance for the font, but not
for the actual laid-out text.
I considered also providing a "defaultBaseline" accessor that returns
the distance for the actual dominant baseline, but it turns out right
now we never decide the baseline is ideographic. We always use the
alphabetic baseline. We should probably fix that...
R=eseidel@chromium.org
Review URL: https://codereview.chromium.org/1200233002.
