Rendering and Animation Issues

Known issues and limits of the Rendering and Animation page in Chart Internals.

Need Verification

Frame cost of large charts is not measured

The issues under Confirmed follow from the code, but none of them has been timed on a device. Before choosing which to fix first, measure frame times for an expanded line chart, a live line window, an expanded stacked area chart, and an expanded histogram at 10,000, 100,000, and 1,000,000 items.

Confirmed

Data with a new point count draws without animation

Line, stacked area, stacked bar, bar, and histogram charts animate an update only when the number of series and points stays the same. Data that goes from 5 points to 6, or adds a series, draws straight away. Live line charts keep the point count fixed and slide the window, so new points still animate there.

Confirmed by the code: LineChartTransitionState.update snaps on a changed series structure, StackedAreaChartImpl keys its ChartMorphState on the series and point counts, and StackedBarChartImpl and rememberBarChartMorph key theirs on the bar count.

Options:

• Morph between the two counts: ChartMorphState already blends lists of different lengths, and new points could start from the last drawn value.

Stacked area builds every point before culling

Each draw blends every point of every series from ChartMorphState, allocates a zero baseline as long as the data, and builds an Offset for every point in buildSeriesPoints, then keeps only the visible range with subList. Culling saves path segments, not the work over every point of every series.

Confirmed by the code: the canvas in StackedAreaChart and buildSeriesPoints.

Options:

• Build points only for the visible range, plus one on each side.

Wide expanded charts show an error instead of drawing

The expanded view sizes its canvas to every item, and Compose constraints cannot hold more than about 262,000 px. Past that, the chart shows "Chart exceeds layout limits" instead of drawing: an expanded line or stacked area chart at 21,847 points, or 5,463 at 4× zoom, and a bar or stacked bar chart with default bar sizes at 4,994 bars on a 2.625 density screen.

Confirmed by ChartCanvasLimitsTest and by the *_expandedPastLayoutLimits_displaysErrorInsteadOfCrashing tests in charts-line, charts-stacked-area, and charts-stacked-bar.

Options:

• Draw on a viewport-sized canvas and offset the drawing by the scroll position, so the canvas no longer grows with the item count. Positions then need to count from the first visible item: past about 8.4 million px, a Float position can no longer hold fractions of a pixel, and past about 16.8 million px it skips every other pixel.