imagepipe 0.5.0

use crate::opbasics::*;

use std::cmp;

#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct OpBaseCurve {
  pub exposure: f32,
  pub points: Vec<(f32, f32)>,
}

impl OpBaseCurve {
  pub fn new(img: &ImageSource) -> OpBaseCurve {
    match img {
      ImageSource::Raw(_) => {
        OpBaseCurve{
          exposure: 0.0,
          // Slopes the curve to go from the linear raw to a more natural look
          points: vec![(0.50, 0.60)],
        }
      },
      ImageSource::Other(_) => {
        OpBaseCurve{
          exposure: 0.0,
          points: vec![],
        }
      }
    }
  }
}

impl<'a> ImageOp<'a> for OpBaseCurve {
  fn name(&self) -> &str {"basecurve"}
  fn run(&self, _pipeline: &PipelineGlobals, buf: Arc<OpBuffer>) -> Arc<OpBuffer> {
    if self.points.len() == 0 && self.exposure.abs() < 0.001 {
      return buf
    }

    let mut final_points = self.points.clone();
    for (_, to) in final_points.iter_mut() {
      *to = *to * self.exposure.exp2();
    }
    let func = SplineFunc::new(&final_points);

    Arc::new(buf.mutate_lines_copying(&(|line: &mut [f32], _| {
      for pix in line.chunks_exact_mut(3) {
        pix[0] = func.interpolate(pix[0]);
      }
    })))
  }
}

impl OpBaseCurve {
  pub fn get_spline(&self) -> SplineFunc {
    SplineFunc::new(&self.points)
  }
}


pub struct SplineFunc {
  points: Vec<(f32,f32)>,
  c1s: Vec<f32>,
  c2s: Vec<f32>,
  c3s: Vec<f32>,
}

impl SplineFunc {
  // Monotone cubic interpolation code adapted from the Javascript example in Wikipedia
  pub fn new(p: &[(f32,f32)]) -> SplineFunc {
    let mut points = Vec::new();
    if p.len() == 0 || (p[0].0 > 0.0 && p[0].1 > 0.0) {
      points.push((0.0, 0.0));
    }
    points.extend_from_slice(p);
    if p.len() == 0 || (p[p.len()-1].0 < 1.0 && p[p.len()-1].1 < 1.0) {
      points.push((1.0, 1.0));
    }

    // Get consecutive differences and slopes
    let mut dxs = Vec::new();
    let mut dys = Vec::new();
    let mut slopes = Vec::new();
    for i in 0..(points.len()-1) {
      let dx = points[i+1].0 - points[i].0;
      let dy = points[i+1].1 - points[i].1;
      dxs.push(dx);
      dys.push(dy);
      slopes.push(dy/dx);
    }
    
    // Get degree-1 coefficients
    let mut c1s = vec![slopes[0]];
    for i in 0..(dxs.len()-1) {
      let m = slopes[i];
      let next = slopes[i+1];
      if m*next <= 0.0 {
        c1s.push(0.0);
      } else {
        let dx = dxs[i];
        let dxnext = dxs[i+1];
        let common = dx + dxnext;
        c1s.push(3.0*common/((common+dxnext)/m + (common + dx)/next));
      }
    }
    c1s.push(slopes[slopes.len()-1]);
  
    // Get degree-2 and degree-3 coefficients
    let mut c2s = Vec::new();
    let mut c3s = Vec::new();
    for i in 0..(c1s.len()-1) {
      let c1 = c1s[i];
      let slope = slopes[i];
      let invdx = 1.0 / dxs[i];
      let common = c1+c1s[i+1] - slope - slope;
      c2s.push((slope-c1-common)*invdx);
      c3s.push(common*invdx*invdx);
    }
  
    SplineFunc {
      points: points,
      c1s: c1s,
      c2s: c2s,
      c3s: c3s,
    }
  }

  pub fn interpolate(&self, val: f32) -> f32 {
    // Anything at or beyond the last value returns the last value
    let end = self.points[self.points.len()-1].0;
    if val >= end {
      return self.points[self.points.len()-1].1;
    }

    // Anything at or under the first value returns the first value
    let first = self.points[0].0;
    if val <= first {
      return self.points[0].1;
    }

    // Search for the interval x is in, returning the corresponding y if x is one of the original xs
    let mut low: isize = 0;
    let mut mid: isize;
    let mut high: isize = (self.c3s.len() - 1) as isize;

    while low <= high {
      mid = (low+high)/2;
      let xhere = self.points[mid as usize].0;
      if xhere < val { low = mid + 1; }
      else if xhere > val { high = mid - 1; }
      else { return self.points[mid as usize].1 }
    }
    let i = cmp::max(0, high) as usize;
    
    // Interpolate
    let diff = val - self.points[i].0;

    self.points[i].1 + self.c1s[i]*diff + self.c2s[i]*diff*diff + self.c3s[i]*diff*diff*diff
  }
}

#[cfg(test)]
mod tests {
  use super::*;

  #[test]
  fn extremes() {
    let spline = SplineFunc::new(&[]);
    assert_eq!(spline.interpolate(0.0), 0.0);
    assert_eq!(spline.interpolate(1.0), 1.0);
  }

  #[test]
  fn saturates() {
    let spline = SplineFunc::new(&[]);
    assert_eq!(spline.interpolate(1.5), 1.0);
    assert_eq!(spline.interpolate(-0.2), 0.0);
  }

  #[test]
  fn high_blackpoint() {
    let spline = SplineFunc::new(&[(0.0,0.2)]);
    assert_eq!(spline.interpolate(0.0), 0.2);
  }

  #[test]
  fn low_whitepoint() {
    let spline = SplineFunc::new(&[(1.0,0.8)]);
    assert_eq!(spline.interpolate(1.0), 0.8);
  }
}