cnlnr opened a new issue, #21703:
URL: https://github.com/apache/echarts/issues/21703
### What problem does this feature solve?
### Use Case & Context
In physical domain modeling, thermodynamics (e.g., phase diagrams showing
P-T relationships), and complex multi-threshold business monitoring, data
visualization needs to show how dynamic parameters interact with
non-linear/curved decision boundaries.
Currently, standard bar charts (`type: 'bar'`) only support fixed threshold
lines or simple linear limits. While users can implement custom shapes using
`type: 'custom'` with raw Canvas rendering (`renderItem`), calculating
collisions and intersections between moving bar vertices and curved threshold
lines (e.g., polynomial/spline boundaries) in a 2D parameter space is complex,
performant-heavy, and difficult to generalize.
### End User Experience
With this feature, users could define smooth/curved boundary paths in the
coordinate system. As bar elements change in position (X-axis) or height
(Y-axis), the chart would automatically compute boundary intersections and
trigger real-time state/phase transitions (e.g., solid, liquid, gas, or custom
status zones) with responsive styling and HiDPI canvas rendering.
### What does the proposed API look like?
We propose extending the `markLine` / `series` capability to support
standard curved boundaries or adding a specialized phase/boundary property
within `type: 'bar'` or `type: 'custom'`:
```javascript
option = {
xAxis: { type: 'value', name: 'Pressure (P)' },
yAxis: { type: 'value', name: 'Temperature (T)' },
series: [
{
type: 'bar',
data: [[2.0, 5.5]], // [X Position, Y Height]
// Proposed API for dynamic curved boundary detection
boundaryDetection: {
enabled: true,
curves: [
{
name: 'Sublimation Curve',
// Function or polynomial points defining the boundary curve
expr: (x) => Math.pow(x, 2) + 1,
states: {
above: { itemStyle: { color: '#ff4d4f' }, label: 'Gas' },
below: { itemStyle: { color: '#1890ff' }, label: 'Solid' }
}
}
]
}
}
]
};
```
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