[FEATURE]: minimum autorange window

Feature request: “minimum autorange window” (default range, expand only when data exceed bounds) for live graphs

Problem / Motivation

We are building a live (streaming) graph with Plotly.js. When using autorange: true, the y-axis can become too tightly zoomed around very small values. This makes it hard to follow the signal comfortably because the scale constantly re-adjusts to tiny changes.

At the same time, we need to see outliers immediately: if a value suddenly exceeds a threshold, the plot should expand so the outlier is visible and operators can react.

So we want a y-axis behavior like:

• Default to a “stable” range (e.g. [-10, 10]) while data stay inside it (prevents over-zooming).
• If any new data point goes below -10 or above 10, automatically expand the axis beyond that window (so outliers are visible).
• In other words: do not shrink inside the window, but do expand outside of it.

Why current options don’t solve it

• layout.yaxis.autorangeoptions.clipmin/clipmax cap the autorange result.
  They prevent the axis from expanding beyond the clip values, which is the opposite of what we need (we want expansion beyond the threshold).
• autorangeoptions.minallowed/maxallowed (and axis-level allowed options) are hard limits / exact values and also do not provide “minimum window but expandable”.
• The current workaround is to compute data min/max and call Plotly.relayout() repeatedly, but this creates boilerplate, can fight user interactions, and is easy to get wrong for multi-axis / overlay cases.

Proposed feature

Add an autorange option that enforces a minimum visible window while still allowing expansion when data exceed the window.

Possible API (one of these, open to better naming):

• yaxis.autorangeoptions.minwindow: [-10, 10]
• yaxis.autorangeoptions.minrange: 20 (minimum span)
• or similar

Proposed semantics

When autorange: true:

1. Compute normal autorange [amin, amax] from data (with existing padding rules).
2. Enforce: the final range must include the data, and must be at least the configured minimum window/span.
   • If data are within the minimum window, use the minimum window exactly (stable view).
   • If data exceed the window, expand as needed to include the data (outliers become visible).

Examples

Given minwindow: [-10, 10]:

• data in [-3, 5] -> range should be [-10, 10]
• data in [-12, 5] -> range should expand to include -12 (e.g. [-12, 10] plus padding if applicable)
• data in [-3, 22] -> range should expand to include 22

Minimal reproduction / demonstration

Current behavior with autorange: true in a streaming graph:

• when values are close to 0, the axis zooms too tightly and keeps changing scale, making the chart hard to read.

Desired behavior:

• keep a stable default range (e.g. [-10, 10]) until thresholds are exceeded, then expand.

(If maintainers want, I can provide a CodePen reproducing the streaming case using Plotly.extendTraces.)

Additional notes

This feature would be especially valuable for:

• live monitoring dashboards
• industrial / IoT telemetry
• finance signals with mostly small fluctuations but occasional spikes

It’s conceptually related to clipmin/clipmax, but with inverse behavior:

• clip* = “don’t expand past these limits”
• minwindow = “don’t shrink inside these limits, but expand past them when necessary”
• or you can add more values in autorangeoptions: include

首先跟踪现有的 yaxis.autorangeoptions 处理逻辑，尤其是 clipmin、clipmax、minallowed 和 maxallowed，并检查 Plotly.extendTraces 和 Plotly.relayout 如何影响流式传输时的 autorange 行为。定义 API，并验证当数据保持在配置的最小窗口内时，autorange 会保留该最小窗口，同时充分扩展以包含异常值和现有的 padding 规则。