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[BUG] HSLColor always renders as solid red, ignoring hue adjustments #696
Description
Describe the bug
Drawing with HSLColor(hue, 1.0, 0.5) produces a solid red image regardless of hue.
Expected behaviour: hue 0 -> red, 120 -> green, 240 -> blue (smooth gradient).
Environment
| Item | Value |
|---|---|
| Plotters version | 0.3.7 |
| Rust version | 1.86.0 |
| OS / Toolchain | Windows 11 |
I'm pulling from cargo.
To Reproduce
use plotters::prelude::*;
use plotters::style::HSLColor;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let root = BitMapBackend::new("hsl_test_output.png", (200, 200)).into_drawing_area();
root.fill(&WHITE)?;
// sweep hue 0° (red) -> 240° (blue) horizontally
for x in 0..200 {
let hue = 240.0 * x as f64 / 200.0;
let color = HSLColor(hue, 1.0, 0.5);
for y in 0..200 {
root.draw_pixel((x as i32, y as i32), &color)?;
}
}
root.present()?;
Ok(())
}Actual output:
Expected output
The same sweep converted manually HSL -> RGB shows the full spectrum:
import numpy as np, matplotlib.pyplot as plt, colorsys, imageio.v3 as iio
w = 200
img = np.zeros((w, w, 3), dtype=np.uint8)
for x in range(w):
hue = 240.0 * x / w / 360.0 # hue in [0,1]
r, g, b = colorsys.hls_to_rgb(hue, 0.5, 1.0)
img[:, x] = (np.array([r, g, b]) * 255).astype(np.uint8)
iio.imwrite("expected_hsl_gradient.png", img)
Activity
zxq82lm commentedon Oct 3, 2025
I opened a PR to fix this: #703.