[scroll] use the exact visible size on macOS, instead of the clip view's size rounded to whole pixels - #112
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…w's size rounded to whole pixels AppKit rounds the clip view's size to whole pixels, so a 99.2 pt scroll view reported a visible size of 99 and its content laid out for 99, while UIKit uses 99.2. The clip view now records the size AppKit asks for before rounding it, so visibleSize, the layout size, contentSize and the scroll range match UIKit's. AppKit still snaps where scrolling comes to rest to the window's pixels, so the edge checks count an offset within a pixel of an edge as at the edge. This also fixes trackpad scroll chaining for nested scroll views at fractional sizes. Fixes #102.
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Included review availability: This review used your included allowance. Your plan provides up to 1 included review per hour; 0 remain after this review. 📝 WalkthroughWalkthroughAppKit scroll views now retain fractional viewport dimensions for visible-size and render-bound calculations. Scroll-edge checks treat offsets within one pixel of a limit as in range. Tests cover fractional dimensions, fitting content, elasticity, and nested gesture routing. ChangesFractional scroll geometry
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix · Severity of issue fixed: Medium Merge Risk: ⚪ Minimal · up to This change keeps fractional scroll-view dimensions on macOS and treats offsets within one pixel of an edge as at the edge. Tests cover the main cases. No merge-blocking risk was found. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to The inspected changes remain confined to scroll geometry and UI event routing, with no demonstrated new security exposure. Interrupted gesture behavior and downstream coverage remain partly unresolved, so the assessment is conservative. Retained concerns Security review detailsSecurity Blast Radius
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Full details: Linked Issues checkExplanation Issue Resolution For each fitting axis, round the document view size to the size that
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@ComposeUI/Sources/ComposeUI/CrossPlatform/ScrollView/ScrollView.swift:
- Line 456: Update ScrollView’s pixelLength to represent content-coordinate
tolerances separately for each axis, using AppKit backing conversion so
magnification is included and retaining the platform fallback. Update
canScrollToBottom and isContentOffsetOutsideScrollableRange to use the
corresponding horizontal or vertical tolerance, and apply the same axis-specific
handling to the other pixelLength comparisons in ScrollView+Scrolling.
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ComposeUI/Sources/ComposeUI/ComposeView/ComposeView.swiftComposeUI/Sources/ComposeUI/CrossPlatform/ScrollView/ScrollView+Scrolling.swiftComposeUI/Sources/ComposeUI/CrossPlatform/ScrollView/ScrollView.swiftComposeUI/Tests/ComposeUITests/ComposeView/ComposeView+RenderBoundsTests.swiftComposeUI/Tests/ComposeUITests/CrossPlatform/ScrollView/ScrollView+ScrollingTests.swiftComposeUI/Tests/ComposeUITests/CrossPlatform/ScrollView/ScrollViewTests.swift
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #112 +/- ##
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Coverage 96.41% 96.41%
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Files 114 114
Lines 7026 7039 +13
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+ Hits 6774 6787 +13
Misses 252 252
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…along each axis On macOS, content offsets are in document points, so on a magnified or scaled scroll view a pixel on screen isn't 1 / windowScaleFactor of them. The tolerance now converts a unit vector along each axis to backing pixels on the clip view, which includes magnification and scaled bounds and keeps the axes apart under rotation.
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…is, instead of by the magnification A caller can scale the clip view's bounds differently along each axis, which the magnification can't express: with 25 × 40 bounds in a 100 × 100 clip view, AppKit reports a magnification of 4 and visibleSize gave 25 × 25. The size the clip view was given now scales by the clip view's bounds-to-frame ratio along each axis, which also covers magnification and stays exact when nothing is scaled.
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Summary
visibleSizereported the rounded 99, andComposeViewlaid out its content for it, while UIKit reports and lays out for 99.2.visibleSize, the sizeComposeViewlays out for,contentSizealong axes where the content fits, andmaxOffsetX/maxOffsetYnow use the exact size, so they match UIKit's values for the same view.canScrollToLeft/Right/Top/Bottomand the gesture routing's out-of-range check count an offset within a pixel of an edge as at the edge.What changed
ScrollView(macOS): a privateNSClipViewsubclass records the size AppKit sets before the clip view rounds it, andvisibleSizereturns it in content coordinates, scaled by the clip view's own bounds-to-frame ratio along each axis, so magnification and any scaling of the clip view's bounds are included (found in review). A replaced clip view falls back to its own bounds size.ComposeView.renderBounds()(macOS): the size is the view's bounds size, without the pixel rounding that matched the clip view.maxOffsetX/maxOffsetYare the content size minus the exact visible size plus the inset, as on UIKit. Along an axis where the content fits, the document keeps the exact size, so the maximum offset is 0.canScrollTo*and the out-of-range check allow one pixel on screen along each axis, measured in content coordinates. On macOS,pixelSizeconverts a unit vector along each axis to backing pixels on the clip view, so magnification and scaled bounds are included (found in review). On UIKit it's1 / windowScaleFactor, since zooming doesn't change the units of the offset.ScrollViewTests: exactvisibleSizeand maximum offsets at a fractional size, including beside a legacy scroll bar, with the clip view's bounds scaled differently along each axis, and at zero size, the fallback for a replaced clip view, elasticity for a document as large as a fractional-size view, and trackpad routing within a pixel of each of the four ends, resting past and short of each, and with bounds scaled differently on each axis.ScrollView_ScrollingTests:canScrollTo*within and beyond a pixel of each edge, on every platform, and on macOS at 4x and 0.25x magnification, with bounds scaled differently on each axis, and rotated 45°.ComposeView_RenderBoundsTests: the three fractional-size tests now expect exact sizes, with the clip view rounding down, up, and through scaled bounds, and check that fitting content doesn't scroll or bounce.canScrollTo*checks and the four out-of-range clauses), comparing elasticity against the rounded clip view on either axis, restoring the old render-bounds rounding, using one uniform1 / windowScaleFactor, converting a whole 1×1 size, swapping the axes in either check, and dividingvisibleSizeby the magnification each fail a test.Decisions
contentSizeand the scroll range match UIKit's. AppKit's own scroll range then includes the sub-pixel leftover, see [scroll] Decide whether macOS should snap a set content offset to pixels, as UIKit does #110 below.render(), that only floating-point noise doesn't count as overflow.constrainBoundsRect(_:)override to pin AppKit's scroll range to the exact one. A probe showed AppKit snaps where scrolling comes to rest past its own range anyway, so the edge checks need the tolerance either way.Not in this PR
visibleSizeis the width beside the bar whileComposeViewlays out for its full bounds, as before.ComposeView's scrolling and fitting content account for content insets #108:ComposeView's scrolling and fitting content don't account for content insets. The elasticity check here doesn't either, as before.Test plan
make formatandmake lint.Fixes #102
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