R/trajectory.R

In ijlyttle/paleval: Tools to help you design and evaluate color palettes

# License: BSD_3_clause
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# YEAR: 2005-2018
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# COPYRIGHT HOLDER: Ross Ihaka, Paul Murrell, Kurt Hornik, Jason C. Fisher, Reto
# Stauffer, Claus O. Wilke, Claire D. McWhite, Achim Zeileis
#
# ORGANIZATION: Ross Ihaka, Paul Murrell, Kurt Hornik, Jason C. Fisher, Reto
# Stauffer, Claus O. Wilke, Claire D. McWhite, Achim Zeileis
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# https://github.com/cran/colorspace/blob/0d206bc2db4bd143710ed28490c4f8b1b05e8ea3/R/hcl_palettes.R#L397

## trajectories
lintrj <- function(i, p1, p2) p2 - (p2 - p1) * i
tritrj <- function(i, j, p1, p2, pm) ifelse(i <= j,
                                            p2 - (p2 - pm) * i/j,
                                            pm - (pm - p1) * abs((i - j)/(1 - j)))

## HCL sequence
seqhcl <- function(i, h1, h2, c1, c2, l1, l2, p1, p2, cmax, fixup, ...) {

  # print(i)
  # print(lintrj(i, h1, h2))

  j <- 1/(1 + abs(cmax - c1) / abs(cmax - c2))
  if (!is.na(j) && (j <= 0 | j >= 1)) j <- NA
  colorspace::hex(colorspace::polarLUV(
    L = lintrj(i^p2, l1, l2),
    C = if(is.na(j)) lintrj(i^p1, c1, c2) else tritrj(i^p1, j, c1, c2, cmax),
    H = lintrj(i, h1, h2)),
    fixup = fixup, ...
  )
}