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#' Skew geometric objects
#'
#' Skew geometric objects by a shear factor in x and y dimension.
#' @param obj [\code{geometric object(1)}]\cr the object to skew.
#' @param x [\code{numeric(1)}]\cr the shear factor in x dimension.
#' @param y [\code{numeric(1)}]\cr the shear factor in y dimension.
#' @param fid [\code{integerish(.)}]\cr in case only a subset of features shall
#' be skewed, specify that here.
#' @param update [\code{logical(1)}]\cr whether or not to update the window slot
#' after skewing.
#' @return \code{geom} of the skewed \code{obj}.
#' @family geometry tools
#' @examples
#' # skew several features
#' visualise(gtGeoms$polygon, linewidth = 3)
#' newPoly <- gt_skew(obj = gtGeoms$polygon, x = 0.5, update = FALSE)
#' visualise(geom = newPoly, linecol = "green", new = FALSE)
#'
#' # skew a single feature
#' visualise(gtGeoms$polygon, linewidth = 3)
#' newPoly <- gt_skew(obj = gtGeoms$polygon, x = 0.5, y = .7, fid = 2,
#' update = FALSE)
#' visualise(newPoly, linecol = "green", new = FALSE)
#' @importFrom checkmate assertNumeric assertIntegerish assertLogical
#' @importFrom tibble tibble as_tibble
#' @importFrom methods new
#' @export
gt_skew <- function(obj, x = NULL, y = NULL, fid = NULL, update = TRUE){
assertNumeric(x = x, any.missing = FALSE, min.len = 1, null.ok = TRUE)
assertNumeric(x = y, any.missing = FALSE, min.len = 1, null.ok = TRUE)
assertNumeric(x = fid, lower = 1, finite = TRUE, any.missing = FALSE, null.ok = TRUE)
assertLogical(x = update, len = 1, any.missing = FALSE)
theFeatures <- getFeatures(x = obj)
theGroups <- getGroups(x = obj)
thePoints <- getPoints(x = obj)
thewindow <- getWindow(x = obj)
# set default values
if(is.null(x)){
x <- 0
}
if(is.null(y)){
y <- 0
}
ids <- unique(thePoints$fid)
# identify fids to modify
existsID <- !is.null(fid)
if(existsID){
doSkew <- ids %in% fid
} else{
doSkew <- rep(TRUE, length(ids))
}
# repeat values to match fids
if(length(x) != length(ids)){
x <- rep(x, length.out = length(ids))
}
if(length(y) != length(ids)){
y <- rep(y, length.out = length(ids))
}
# modify vertices
temp <- NULL
for(i in seq_along(ids)){
tempCoords <- thePoints[thePoints$fid == ids[i],]
newCoords <- tempCoords
if(doSkew[i]){
centCoords <- tempCoords[!duplicated(tempCoords),]
centroid <- tibble(x = mean(x = centCoords$x), y = mean(x = centCoords$y))
newCoords$x <- tempCoords$x + x[[i]] * tempCoords$y
newCoords$y <- tempCoords$y + y[[i]] * tempCoords$x
centCoords <- newCoords[!duplicated(newCoords),]
newCentroid <- tibble(x = mean(x = centCoords$x), y = mean(x = centCoords$y))
offset <- newCentroid - centroid
newCoords$x <- newCoords$x - offset$x
newCoords$y <- newCoords$y - offset$y
}
temp <- rbind(temp, newCoords)
}
# update window
if(update){
window <- .updateWindow(input = temp, window = thewindow)
} else {
window <- thewindow
}
# make history
if(length(ids) == 1){
hist <- paste0("geom was skewed.")
} else {
hist <- paste0("geoms were skewed.")
}
# make new geom
out <- new(Class = "geom",
type = getType(x = obj)[1],
point = as_tibble(temp),
feature = theFeatures,
group = theGroups,
window = window,
crs = getCRS(x = obj),
history = c(getHistory(x = obj), list(hist)))
return(out)
}
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