Surface::surface_color has the wrong type: it should be a 2D numeric array, not Vec<Box<dyn Color>>

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Issue 类型
缺陷
描述清晰度
基本清楚
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技术栈
rust
领域
data-visualization

调研方向

Start in plotly/src/traces/surface.rs by reviewing the Surface surface_color field and the serialize_surface unit test. Check the proposed 2D numeric representation against the reproduction and expected JSON, then resolve the public API choice before updating the field and test. Done means nested numeric values compile and serialize as a 2D surfacecolor array.

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描述

Description

In plotly/src/traces/surface.rs, the surfacecolor attribute of the Surface trace is defined as:

#[serde(rename = "surfacecolor")]
surface_color: Option<Vec<Box<dyn Color>>>,

This doesn't match plotly.js. There, surface.surfacecolor is a data array:

Sets the surface color values, used for setting a color scale independent of z.

The naming in this case is misleading and might have resulted in the current state. Plotly.js expects a 2D numeric matrix with the same shape as z and not some of the common string color representations that Plotly.js can digest. The numeric values are mapped through colorscale (and cmin/cmax/cmid) in place of z. A common use is e.g. coloring a surface by a second scalar field, e.g. showing temperature on a height map.

The current type causes two problems:

  1. It's only one-dimensional. Color is implemented for numeric types such as f64, so .surface_color(vec![0.1, 0.2, ...]) compiles. But it can't express [[...], [...]], because Vec<f64> doesn't implement Color.
  2. It suggests CSS colors. Because of the Color bound, users and the existing unit test pass values like "#123456". Plotly.js doesn't accept those for this attribute.

Reproduction

use plotly::{Plot, Surface};

fn main() {
    let z = vec![vec![0.0, 1.0], vec![1.0, 2.0]];
    let c = vec![vec![2.0, 0.0], vec![0.0, 2.0]];

    let trace = Surface::new(z)
        .x(vec![0.0, 1.0])
        .y(vec![0.0, 1.0])
        .surface_color(c); // does not compile: `Vec<{float}>` does not implement `Color`

    let mut plot = Plot::new();
    plot.add_trace(trace);
    plot.show();
}

The existing unit test serialize_surface also expects JSON that plotly.js treats as invalid for this attribute:

.surface_color(vec!["#123456"])
// ...
"surfacecolor": ["#123456"],

Expected behaviour

You can pass a 2D numeric array with the same shape as z, and it serializes as:

"surfacecolor": [[2.0, 0.0], [0.0, 2.0]]

Proposed fix

Change the field to a 2D numeric array, for example:

#[serde(rename = "surfacecolor")]
surface_color: Option<Vec<Vec<f64>>>,

and update the serialize_surface test:

.surface_color(vec![vec![0.0, 1.0]])
// ...
"surfacecolor": [[0.0, 1.0]],

Considerations

  • A 4th generic parameter Surface<X, Y, Z, C = f64> with surface_color: Option<Vec<Vec<C>>>. This is could be more flexible. Default type parameters on structs are allowed, but they aren't used when inferring the type of Surface::new(...), so some existing call sites could still stop compiling.
  • Reuse Z, i.e. Option<Vec<Vec<Z>>>. This is simpler, but it forces the color values to have the same type as z.

Environment

  • plotly crate version: 0.14.1
  • Rust version: rustc 1.98.1
  • OS: Windows

This would change the public API and might therefore be a breaking change. As this a fix to feature that was not working consider which level of release version this should result in.

I'm happy to open a PR once we agree on the preferred type.

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