# fields, Tools for spatial data
# Copyright 2004-2007, Institute for Mathematics Applied Geosciences
# University Corporation for Atmospheric Research
# Licensed under the GPL -- www.gpl.org/licenses/gpl.html
"drape.color" <- function(z, col = tim.colors(64), 
    zlim = NULL, transparent.color = "white", midpoint = TRUE) {
    # slight increase for range
    eps <- 1e-07
    # range if zlim not supplied
    if (is.null(zlim)) {
        zlim <- range(c(z), na.rm = TRUE)
    }
    # set any values outside of range to NA ( i.e. the transparent.color)
    z[(z < zlim[1]) | (z > zlim[2])] <- NA
    NC <- length(col)
    M <- nrow(z)
    N <- ncol(z)
    # if midpoint is TRUE find average z value for a facet and
    # overwrite z with matrix where row and column are one less
    # (reflecting that these are box centers not corners)
    if (midpoint) {
        z <- (z[1:(M - 1), 1:(N - 1)] + z[2:M, 1:(N - 1)] + z[1:(M - 
            1), 2:N] + z[2:M, 2:N])/4
    }
    # spacing for grid to assign  colors
    # 1+eps included so that if z== zlim[2] it gets a color
    dz <- (zlim[2] * (1 + eps) - zlim[1])/NC
    # discretize the z-value
    zcol <- floor((z - zlim[1])/dz + 1)
    # assign colors if in range 1:NC otherwise use the transparent color
    ifelse(zcol > NC, transparent.color, col[zcol])
}