Zoom viewport-centre anchoring (follow-up to #33, stacked on #34)#38
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andrewtheart wants to merge 2 commits into
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Zoom viewport-centre anchoring (follow-up to #33, stacked on #34)#38andrewtheart wants to merge 2 commits into
andrewtheart wants to merge 2 commits into
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Introduce a small IScrollOffsetSource abstraction so the editor scroll position is expressed in pixels rather than legacy scrollbar units (SingleLineHeight / DefaultVerticalScrollSensitivity). ScrollManager routes every offset read/write through it; the ScrollBarOffsetSource adapter backs it with the existing two ScrollBar primitives and does the pixel<->scrollbar-unit conversion internally (ScrollOffsetMath). Behavior is unchanged. Foundation for word-wrap scrolling, long-line horizontal virtualization and diagonal 2-axis touchpad scrolling (FrozenAssassine#33). Adds ScrollOffsetMathTests.
ZoomManager.UpdateZoom re-anchors the pixel offset seam so the document row under the vertical viewport centre stays stationary across a font-size change instead of drifting; horizontal scales by the font-size ratio. Pure math extracted to ZoomScrollAnchor + unit tests. Follow-up to FrozenAssassine#33, builds on FrozenAssassine#34.
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Follow-up to #33: zoom viewport-centre anchoring
A small quality-of-life follow-up that builds directly on the #34 seam.
Problem
When you zoom (Ctrl+wheel / pinch / a zoom command), the font size changes but the raw pixel scroll offset
stays the same — so the row under your eyes drifts, because the same pixel offset now maps to a different
row once the line height changes. Zooming feels like the document slides around.
Fix
ZoomManager.UpdateZoomnow re-anchors the pixel scroll seam so the document row under the verticalviewport centre stays stationary across the zoom. The horizontal axis scales by the font-size ratio so the
left-most visible column stays roughly put too.
The line height is
ZoomedFontSize + LineSpacingPadding, and the format is only rebuilt on the next draw, sothe old line height is snapshotted at the top of
UpdateZoombefore the new font size is computed. Thearithmetic is extracted into a pure
ZoomScrollAnchor(vertical centre-row preservation + horizontal ratioscale) and unit-tested;
ZoomManagerjust wires it to the offset source.Changes
Core/ZoomScrollAnchor.cs— pure anchor math (+ZoomScrollAnchorTests).Core/ZoomManager.cs— snapshot old line height, callAnchorScrollAcrossZoomthrough the offset source(adds a
ScrollManagerdependency).Core/TextLayoutManager.cs— names the line-spacing padding asLineSpacingPadding(was an inline+ 2)so the post-zoom line height can be computed before the format rebuilds.
Verification
Behavior is unchanged except the anchor (guarded to no-op before the first real layout). Library + test
project build clean (x64).