Documentation / @finchart/core / index / DecimationStrategy
Interface: DecimationStrategy<T>
Defined in: packages/core/src/data/types.ts:255
Type Parameters
T
T extends BaseDataPoint = BaseDataPoint
Properties
indexAnchored?
readonlyoptionalindexAnchored?:true
Defined in: packages/core/src/data/types.ts:261
Ask a data manager to retain an x anchor when indices shift after a prepend. An implementation using tiers must keep the anchor bar in each reduced array so its index remains a bucket boundary.
Methods
decimate()
decimate(
data,range,threshold,screenXScan?,gapFree?):T[]
Defined in: packages/core/src/data/types.ts:292
Decimates only the [range.start, range.end) window, not all of data.
Why the window is a range, not an array: if the caller copied the visible range with slice, that's a big new array every frame on large data, most of it thrown away unused. Why the range is required, not optional: if it were optional, a strategy that doesn't know the range could decimate the whole array and the type system wouldn't catch it.
screenXScan is a factory that opens a pass for screen-place lookups (see Viewport.screenXScan). A strategy that buckets by x (M4Decimation, LttbDecimation) has to bucket in that same space when the screen space differs. Each sweep opens one pass — the cursor belongs to that pass, so strategies and frames can't interfere with each other. If absent, x is the screen place (continuous coordinate space, the default).
gapFree is a fact the caller already knows — if true, this data is guaranteed gap-free, so the window scan that would otherwise find gap boundaries is skipped. Gap presence is a property of the array, not the window, so the viewport cache can't save this for you — only the side that owns the changes can maintain it incrementally.
Not merged with gapless — that's a static fact about the accessor, this is runtime state of the array.
False covers "don't know," not just "has gaps" — the safe default is false. Passing true incorrectly swallows gaps, and the line runs straight across a spot that should have no value.
Parameters
data
T[]
range
threshold
number
screenXScan?
() => (x) => number
gapFree?
boolean
Returns
T[]