[BUG] Negative tick_mark_size moves labels into plot area instead of only changing tick direction

[chantakan]

Describe the bug

When using set_tick_mark_size with negative values, the intention is to make only the tick marks point inward (into the plot area), which is a common style in scientific papers. However, three problems occur:

1. Labels move with tick marks: The numeric tick labels and axis descriptions also move into the plot area, instead of staying in their original positions outside the plot.

2. Axis description overlaps with numeric labels: Because both move inward, the y-axis description ("y (nondimensional)") overlaps with the numeric tick labels.

3. White background hides grid lines: The moved labels have a white background that covers the grid lines behind them.

Expected behavior:

• Only the tick marks should point inward
• Numeric labels and axis descriptions should remain outside the plot area (their normal positions)
• Similar to matplotlib's ax.tick_params(direction='in')

Actual behavior:

• Tick marks, numeric labels, and axis descriptions all move into the plot area
• Labels overlap each other
• Grid lines are hidden by white label backgrounds

To Reproduce

use plotters::prelude::*;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let root = BitMapBackend::new("inward_ticks.png", (800, 600)).into_drawing_area();
    root.fill(&WHITE)?;

    let mut chart = ChartBuilder::on(&root)
        .margin(10)
        .x_label_area_size(40)
        .y_label_area_size(60)
        .build_cartesian_2d(-4.0f32..4.0f32, -4.0f32..4.0f32)?;

    chart
        .configure_mesh()
        .x_desc("x (nondimensional)")
        .y_desc("y (nondimensional)")
        .set_tick_mark_size(LabelAreaPosition::Left, -5)
        .set_tick_mark_size(LabelAreaPosition::Bottom, -5)
        .draw()?;

    root.present()?;
    Ok(())
}

Version Information

• plotters: 0.3.7 (from crates.io)
• rustc: 1.87.0 (17067e9ac 2025-05-09)
• OS: Ubuntu 24.04.3 LTS