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//! Dave Green's 'cubehelix' colour scheme. //! See cubehelix homepage at: //! https://www.mrao.cam.ac.uk/~dag/CUBEHELIX/ //! Calculation from: //! http://astron-soc.in/bulletin/11June/289392011.pdf //! # Examples //! ``` //! use cube_helix::CubeHelix; //! # fn main() { //! // Get default values //! let ch: CubeHelix = Default::default(); //! // Returns color white: (255,255,255) //! let colors = ch.get_color(1.0); //! # } //! ``` use std::f64::consts::PI; // RGB perceived intensity const /// Red perceived intensity cons const RPIC: (f64, f64) = (-0.14861, 1.78277); /// Green perceived intensity cons const GPIC: (f64, f64) = (-0.29227, -0.90649); /// Blue perceived intensity cons const BPIC: (f64, f64) = (1.97294, 0.0); /// # Examples /// Using default values: /// ``` /// use cube_helix::CubeHelix; /// # fn main() { /// // Get default values /// let ch: CubeHelix = Default::default(); /// // Returns color white: (255,255,255) /// let color = ch.get_color(1.0); /// assert_eq!(color.0, 255); /// assert_eq!(color.1, 255); /// assert_eq!(color.2, 255); /// # } /// ``` /// Using defaults partially: /// ``` /// use cube_helix::CubeHelix; /// // Override 'start' and 'rotation' values /// let ch = CubeHelix { start: 0.2, rotations: 1.5, ..Default::default() }; /// // Returns color black: (0,0,0) /// let color = ch.get_color(0.0); /// assert_eq!(color.0, 0); /// assert_eq!(color.1, 0); /// assert_eq!(color.2, 0); /// ``` #[derive(Debug)] pub struct CubeHelix { /// Gamma factor. pub gamma: f64, /// Starting angle: 0.5 -> purple pub start: f64, /// Rotations (1.5 : R -> G -> B -> R). /// Negative value will 'spin' in opposite direction. pub rotations: f64, /// Value from 0..1 to control saturation. /// Zero value is completelly grayscale. pub saturation: f64, /// Lowest value in value range. This value represents black. pub min: f64, /// Highest value in value range. This value represents white. pub max: f64, } /// Default values to produce the same gradient as D.A Green's paper in Figure 1. /// gamma: 1.0 /// start: 0.5 /// rotations: -1.5 /// saturation: 1.0 /// min: 0.0 /// max: 1.0 impl Default for CubeHelix { fn default() -> CubeHelix { CubeHelix { gamma: 1.0, start: 0.5, rotations: -1.5, saturation: 1.0, min: 0.0, max: 1.0, } } } /// Adds color calculation to CubeHelix struct impl CubeHelix { /// Calculates CubeHelix color for given value. /// Value must be in the min..max range. /// Returns a tuple with three values: (red: u8, green: u8, blue: u8). /// # Examples /// ``` /// use cube_helix::CubeHelix; /// # fn main() { /// // Use range 0..100 - defalts otherwise /// let ch = CubeHelix { min: 0.0, max: 100.0, ..Default::default() }; /// // Get color in the middle. Returns color: (174,97,158) /// let color = ch.get_color(50.0); /// assert_eq!(color.0, 174); /// assert_eq!(color.1, 97); /// assert_eq!(color.2, 158); /// # } /// ``` pub fn get_color(&self, value: f64) -> (u8, u8, u8) { let rgb: (f64, f64, f64) = calc(self, value); ((rgb.0 * 255.0) as u8, (rgb.1 * 255.0) as u8, (rgb.2 * 255.0) as u8) } } /// Use cubehelix color calculation without CubeHelix struct. /// Returns a tuple with three values (red: u8, green: u8, blue: u8) /// # Examples /// ``` /// use cube_helix::color; /// # fn main() { /// // Returns color (181, 104, 101) /// let color = color(1.0, 0.2, -1.5, 1.0, 0.0, 1.0, 0.5); /// assert_eq!(color.0, 181); /// assert_eq!(color.1, 104); /// assert_eq!(color.2, 101); /// # } /// ``` pub fn color( gamma: f64, start: f64, rotations: f64, saturation: f64, min: f64, max: f64, value: f64, ) -> (u8, u8, u8) { let rgb: (f64, f64, f64) = calc( &CubeHelix {gamma, start, rotations, saturation, min, max}, value, ); ((rgb.0 * 255.0) as u8, (rgb.1 * 255.0) as u8, (rgb.2 * 255.0) as u8) } fn calc(cube_helix: &CubeHelix, value: f64) -> (f64, f64, f64) { // normalize value to min-max range let x: f64 = normalize(value, cube_helix.min, cube_helix.max); // Apply gamma factor to emphasise low or high intensity values let lambda: f64 = x * cube_helix.gamma; // Calculate amplitude of deviation let amplitude: f64 = amplitude(lambda, cube_helix.saturation); // Calculate angle of deviation let phi: f64 = phi(cube_helix, value); // Calculate rgb values let red: f64 = color_calc(lambda, amplitude, phi, RPIC); let green: f64 = color_calc(lambda, amplitude, phi, GPIC); let blue: f64 = color_calc(lambda, amplitude, phi, BPIC); (red, green, blue) } // lambda: given value normalized and gamma corrected // (value between 0-1 via normalized) // amplitude: deviation of amplitude in the black and white line // phi: deviation of angle in the black and white diagonal line // color_const: perceived intesity constant tuple for red, green or blue fn color_calc(lambda: f64, amplitude: f64, phi: f64, color_const: (f64, f64)) -> f64 { lambda + amplitude * (color_const.0 * phi.cos() + color_const.1 * phi.sin()) } // phi: deviation of angle in the black and white diagonal line // φ = 2π(s/3 + rλ) fn phi(cube_helix: &CubeHelix, value: f64) -> f64 { 2.0 * PI * (cube_helix.start / 3.0 + cube_helix.rotations * value) } // amplitude: deviation of amplitude in the black and white line // // Calculate amplitude and angle of deviation from the black // to white diagonal in the plane of constant // perceived intensity. // a = hλ(1 − λ)/2 fn amplitude(lambda: f64, saturation: f64) -> f64 { saturation * lambda * (1.0 - lambda) / 2.0 } // Normalize value in the range of min..max to 0..1 fn normalize(value: f64, min: f64, max: f64) -> f64 { if value < min || value > max { panic!("Value: {:?} not in range: {:?} - {:?}", value, min, max); } if min > max { panic!("Incorrect range: min > max"); } if (min - max).signum() == 0.0 { panic!("Incorrect range: {:?} - {:?}", min, max); } (value - min) / (max - min) } //Unit tests for functions and structs in this file. #[cfg(test)] mod cube_helix_tests { use super::*; // Struct tests #[test] fn defaults() { let ch: CubeHelix = Default::default(); assert_eq!(ch.gamma, 1.0); assert_eq!(ch.start, 0.5); assert_eq!(ch.rotations, -1.5); assert_eq!(ch.saturation, 1.0); assert_eq!(ch.min, 0.0); assert_eq!(ch.max, 1.0); } #[test] fn partial_defaults() { let ch = CubeHelix { start: 0.2, rotations: 1.5, ..Default::default() }; assert_eq!(ch.gamma, 1.0); assert_eq!(ch.start, 0.2); assert_eq!(ch.rotations, 1.5); assert_eq!(ch.saturation, 1.0); assert_eq!(ch.min, 0.0); assert_eq!(ch.max, 1.0); } #[test] fn odd_start_and_rotations() { let ch = CubeHelix { start: 77.2, rotations: -21.5, ..Default::default() }; let color = ch.get_color(0.3); assert_eq!(color.0, 124); assert_eq!(color.1, 54); assert_eq!(color.2, 65); } // Color call tests #[test] fn partial_fn_call() { let color = color(1.0, 0.2, -1.5, 1.0, 0.0, 1.0, 0.5); assert_eq!(color.0, 181); assert_eq!(color.1, 104); assert_eq!(color.2, 101); } #[test] fn max_is_white() { let ch: CubeHelix = Default::default(); let colors = ch.get_color(1.0); assert_eq!(colors.0, 255); assert_eq!(colors.1, 255); assert_eq!(colors.2, 255); } #[test] fn min_is_black() { let ch: CubeHelix = Default::default(); let colors = ch.get_color(0.0); assert_eq!(colors.0, 0); assert_eq!(colors.1, 0); assert_eq!(colors.2, 0); } // Tests for normalize #[test] fn normalize_with_defaults() { assert_eq!(normalize(0.5, 0.0, 1.0), 0.5); assert_eq!(normalize(0.2, 0.0, 1.0), 0.2); assert_eq!(normalize(0.0, 0.0, 1.0), 0.0); assert_eq!(normalize(1.0, 0.0, 1.0), 1.0); } // Panic: if user tries to normalize value that is not in his min-max range, // the given rgb value would most likely be unwanted. #[test] #[should_panic] fn normalize_with_value_not_in_range() { assert_eq!(normalize(-0.5, 0.0, 1.0), 666.0); } #[test] fn normalize_with_negative_to_positive_range() { assert_eq!(normalize(0.0, -0.5, 0.5), 0.5); assert_eq!(normalize(0.5, -0.5, 0.5), 1.0); assert_eq!(normalize(-0.5, -0.5, 0.5), 0.0); assert_eq!(normalize(0.2, -0.5, 0.5), 0.7); } // It is better to panic rather than have implicit behaviour. // If min and max value are the same: division with zero value would occur // Possible implicit behaviour could be just to return value 1.0. #[test] #[should_panic] fn normalize_with_incorrect_range() { assert_eq!(normalize(1.1, 1.1, 1.1), 0.0); } }