Understanding Linear Gradients in Line Plots

Oct 13, 2025 by wbrum.org 88 views

Understanding Linear Gradients in Line Plots

When working with line plots, linear gradients can be a powerful tool to visualize data trends and patterns. However, there are situations where the default behavior of linear gradients may not meet our expectations. In this article, we will explore how to specify a custom range for line gradients in line plots.

The Issue with Default Linear Gradients

By default, linear gradients in line plots use the Y data range to interpolate the color. This means that the color of each point on the line is determined by its corresponding Y value. While this approach can be useful in many cases, it can lead to unexpected results when the data does not cover the entire applicable range.

A Real-World Example

Let's consider a scenario where we are plotting grades using a red-yellow-green color scheme. The grades in the chart are between 50% and 100%. However, the color scheme is designed to map grades between 0% and 100%. As a result, a 50% grade will be displayed as red, whereas it should be yellow.

Specifying a Custom Range for Line Gradients

To address this issue, we need to specify a custom range for the line gradient. This can be achieved by using the Series::with_y_range method to set a custom Y range for the series. However, as mentioned earlier, this approach is ignored when using Line::with_gradient.

A Possible Solution

One possible solution is to use a custom gradient function that takes into account the custom range. This can be achieved by creating a custom gradient function that maps the Y values to the desired color range.

Example Code

Here is an example code snippet that demonstrates how to create a custom gradient function:

use plotters::prelude::*;

fn main() {
    let root = BitMapBackend::new("line_gradient.png", (800, 600)).into_drawing_area();
    root.fill(&WHITE).unwrap();

    let mut chart = ChartBuilder::on(&root)
        .caption("Line Gradient", ("sans-serif", 20).into_font())
        .build_cartesian_2d(0f32..100f32, 0f32..100f32)
        .unwrap();

    chart.configure_mesh().draw().unwrap();

    let data = vec![
        (50f32, 50f32),
        (75f32, 75f32),
        (100f32, 100f32),
    ];

    chart
        .draw_series(LineSeries::new(
            data.iter().map(|(x, y)| (*x, *y)),
            &RED,
            &GREEN,
            2f32,
        ))
        .label("Line Gradient")
        .legend(|(x, y)| PathElement::new(vec2(x, y), &RED));

    chart
        .configure_series_labels()
        .background_style(&WHITE.mix(0.8))
        .border_style(&BLACK)
        .draw();
}

In this example, we create a custom gradient function using the LineSeries::new method. We pass in the data points, the start color, the end color, and the line width. We also specify a custom label for the series.

Conclusion

In conclusion, specifying a custom range for line gradients in line plots can be achieved by using a custom gradient function. This approach allows us to take into account the custom range and map the Y values to the desired color range. By following the example code snippet provided, you can create a custom gradient function that meets your specific needs.

Custom Gradient Function

Here is an example of a custom gradient function that maps the Y values to the desired color range:

fn custom_gradient(x: f32, y: f32) -> (f32, f32) {
    let min = 50f32;
    let max = 100f32;
    let range = max - min;

    let scaled_y = (y - min) / range;
    let color = if scaled_y < 0.5 {
        (1.0, 0.0) // Red
    } else if scaled_y < 0.75 {
        (1.0, 1.0) // Yellow
    } else {
        (0.0, 1.0) // Green
    };

    (x, color)
}

This custom gradient function takes into account the custom range and maps the Y values to the desired color range. You can use this function in conjunction with the LineSeries::new method to create a custom gradient function that meets your specific needs.

Custom Gradient Function with Custom Range

Here is an example of a custom gradient function that takes into account a custom range:

fn custom_gradient_with_range(x: f32, y: f32, range: (f32, f32)) -> (f32, f32) {
    let (min, max) = range;
    let scaled_y = (y - min) / (max - min);
    let color = if scaled_y < 0.5 {
        (1.0, 0.0) // Red
    } else if scaled_y < 0.75 {
        (1.0, 1.0) // Yellow
    } else {
        (0.0, 1.0) // Green
    };

    (x, color)
}

This custom gradient function takes into account a custom range and maps the Y values to the desired color range. You can use this function in conjunction with the LineSeries::new method to create a custom gradient function that meets your specific needs.

Conclusion

Q: What is the default behavior of linear gradients in line plots?

A: The default behavior of linear gradients in line plots is to use the Y data range to interpolate the color. This means that the color of each point on the line is determined by its corresponding Y value.

Q: Why is the default behavior of linear gradients not suitable for all cases?

A: The default behavior of linear gradients is not suitable for all cases because it assumes that the data covers the entire applicable range. However, in many cases, the data may not cover the entire range, leading to unexpected results.

Q: How can I specify a custom range for line gradients?

A: You can specify a custom range for line gradients by using a custom gradient function that takes into account the custom range. This can be achieved by creating a custom gradient function that maps the Y values to the desired color range.

Q: What is a custom gradient function?

A: A custom gradient function is a function that takes into account a custom range and maps the Y values to the desired color range. This function can be used in conjunction with the LineSeries::new method to create a custom gradient function that meets your specific needs.

Q: How do I create a custom gradient function?

A: You can create a custom gradient function by defining a function that takes into account the custom range and maps the Y values to the desired color range. Here is an example of a custom gradient function:

fn custom_gradient(x: f32, y: f32) -> (f32, f32) {
    let min = 50f32;
    let max = 100f32;
    let range = max - min;

    let scaled_y = (y - min) / range;
    let color = if scaled_y < 0.5 {
        (1.0, 0.0) // Red
    } else if scaled_y < 0.75 {
        (1.0, 1.0) // Yellow
    } else {
        (0.0, 1.0) // Green
    };

    (x, color)
}

Q: How do I use a custom gradient function with the `LineSeries::new` method?

A: You can use a custom gradient function with the LineSeries::new method by passing the custom gradient function as the third argument. Here is an example:

let data = vec![
    (50f32, 50f32),
    (75f32, 75f32),
    (100f32, 100f32),
];

chart
    .draw_series(LineSeries::new(
        data.iter().map(|(x, y)| (*x, *y)),
        &RED,
        custom_gradient,
        2f32,
    ))
    .label("Line Gradient")
    .legend(|(x, y)| PathElement::new(vec2(x, y), &RED));

Q: Can I specify a custom range for line gradients using the `Series::with_y_range` method?

A: No, you cannot specify a custom range for line gradients using the Series::with_y_range method. This method is ignored when using Line::with_gradient.

Q: What are some common use cases for specifying a custom range for line gradients?

A: Some common use cases for specifying a custom range for line gradients include:

Plotting grades or scores using a red-yellow-green color scheme
Plotting temperatures using a blue-red color scheme
Plotting financial data using a green-red color scheme

Q: How do I troubleshoot issues with custom gradient functions?

A: You can troubleshoot issues with custom gradient functions by:

Checking the custom gradient function for errors
Verifying that the custom gradient function is being called correctly
Using a debugger to step through the custom gradient function and identify the issue

Q: Can I use custom gradient functions with other types of plots?

A: Yes, you can use custom gradient functions with other types of plots, such as bar plots and scatter plots. However, the syntax and implementation may vary depending on the specific plot type and library being used.