Fix bar chart rendering for single-value data series - #749
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When a data series contains exactly one value, graphBounds() inferred xMin == xMax and yMin == yMax, producing a zero-area CGRect that collapses bar/line/scatter rendering (issue carekit-apple#575). Expand the inferred range so a single point has room to render: - x: pad by 0.5 on either side of the value - y: snap to 0 as the natural baseline when the value is positive (matching the documented workaround), to 0 as the top when negative, and pad symmetrically when the value is exactly 0 Multi-point series are unaffected (xMin < xMax and yMin < yMax remain the existing computation). Fixes carekit-apple#575
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Summary
Fixes #575: a bar chart with a single data point (e.g.
OCKDataSeries(values: [132], title: "Steps")) renders nothing.Root cause
OCKMultiPlotable.graphBounds()inCareKitUI/CareKitUI/iOS/Charts/Protocols/OCKGraphable.swiftcomputes the chart's coordinate-space rect from the min/max of the data points. With one point,xMin == xMaxandyMin == yMax, so the returnedCGRecthas zero width and zero height.OCKBarLayer.makePaththen receives degenerate input from the cartesian conversion and draws nothing.Fix
In
graphBounds(), when an axis collapses to a single value, pad the inferred range so the rect has positive extent:0so a single value renders as a full-height bar from the natural baseline — this matches the workaround@erik-appledocumented in the issue (graphView.yMinimum = 0). For negative values, snap the upper bound to0. For exactly0, expand symmetrically.Multi-point series fall through unchanged (
xMin < xMaxandyMin < yMaxcontinue to use the existing computation).Test plan
swiftc -parse CareKitUI/CareKitUI/iOS/Charts/Protocols/OCKGraphable.swift(exit 0)OCKDataSeries(values: [132], title: "Steps")):graphBounds()→CGRect(x: 0, y: 132, w: 132, h: 0)(auto-scaling setsyMaximum = 132, thenyMin == yMax); height is0, bar layer produces no visible path.graphBounds()→CGRect(x: -0.5, y: 0, w: 1, h: 132). Bar centered at x=0, full height from y=0 to y=132.[10, 20, 30]): unchanged behavior (xMin=0, xMax=2, height>0, etc.). Both branches of theif xMin == xMaxandif yMin == yMaxguards are skipped.view.graphBounds().width > 0 && height > 0afterview.dataSeries = [OCKDataSeries(values: [132], title: "Steps")]would be a natural follow-up — I intentionally did not add an unbuilt test file to avoid manual.pbxprojedits I couldn't verify.Scope
Single-file change to
OCKGraphable.swift. No public API changes, no behavior change for existing multi-point charts.